rfc4346.txt   draft-ietf-tls-rfc4346-bis-09.txt >
INTERNET-DRAFT Tim Dierks
Network Working Group T. Dierks Obsoletes (if approved): RFC 3268, 4346, 4366 Independent
Request for Comments: 4346 Independent Updates (if approved): RFC 4492 Eric Rescorla
Obsoletes: 2246 E. Rescorla Intended status: Proposed Standard Network Resonance, Inc.
Category: Standards Track RTFM, Inc. <draft-ietf-tls-rfc4346-bis-09.txt> February 2008 (Expires August 2008)
April 2006
The Transport Layer Security (TLS) Protocol The Transport Layer Security (TLS) Protocol
Version 1.1 Version 1.2
Status of This Memo Status of this Memo
This document specifies an Internet standards track protocol for the By submitting this Internet-Draft, each author represents that any
Internet community, and requests discussion and suggestions for applicable patent or other IPR claims of which he or she is aware
improvements. Please refer to the current edition of the "Internet have been or will be disclosed, and any of which he or she becomes
Official Protocol Standards" (STD 1) for the standardization state aware will be disclosed, in accordance with Section 6 of BCP 79.
and status of this protocol. Distribution of this memo is unlimited.
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2008).
Abstract Abstract
This document specifies Version 1.1 of the Transport Layer Security This document specifies Version 1.2 of the Transport Layer Security
(TLS) protocol. The TLS protocol provides communications security (TLS) protocol. The TLS protocol provides communications security
over the Internet. The protocol allows client/server applications to over the Internet. The protocol allows client/server applications to
communicate in a way that is designed to prevent eavesdropping, communicate in a way that is designed to prevent eavesdropping,
tampering, or message forgery. tampering, or message forgery.
Table of Contents Table of Contents
1. Introduction ....................................................4 1. Introduction 4
1.1. Differences from TLS 1.0 ...................................5 1.1. Requirements Terminology 5
1.2. Requirements Terminology ...................................5 1.2. Major Differences from TLS 1.1 5
2. Goals ...........................................................5 2. Goals 6
3. Goals of This Document ..........................................6 3. Goals of This Document 7
4. Presentation Language ...........................................6 4. Presentation Language 7
4.1. Basic Block Size ...........................................7 4.1. Basic Block Size 7
4.2. Miscellaneous ..............................................7 4.2. Miscellaneous 7
4.3. Vectors ....................................................7 4.3. Vectors 8
4.4. Numbers ....................................................8 4.4. Numbers 9
4.5. Enumerateds ................................................8 4.5. Enumerateds 9
4.6. Constructed Types ..........................................9 4.6. Constructed Types 10
4.6.1. Variants ...........................................10 4.6.1. Variants 10
4.7. Cryptographic Attributes ..................................11 4.7. Cryptographic Attributes 11
4.8. Constants .................................................12 4.8. Constants 13
5. HMAC and the Pseudorandom Function .............................12 5. HMAC and the Pseudorandom Function 14
6. The TLS Record Protocol ........................................14 6. The TLS Record Protocol 15
6.1. Connection States .........................................15 6.1. Connection States 16
6.2. Record layer ..............................................17 6.2. Record layer 18
6.2.1. Fragmentation ......................................17 6.2.1. Fragmentation 19
6.2.2. Record Compression and Decompression ...............19 6.2.2. Record Compression and Decompression 20
6.2.3. Record Payload Protection ..........................19 6.2.3. Record Payload Protection 21
6.2.3.1. Null or Standard Stream Cipher ............20 6.2.3.1. Null or Standard Stream Cipher 21
6.2.3.2. CBC Block Cipher ..........................21 6.2.3.2. CBC Block Cipher 22
6.3. Key Calculation ...........................................24 6.2.3.3. AEAD ciphers 24
7. The TLS Handshaking Protocols ..................................24 6.3. Key Calculation 25
7.1. Change Cipher Spec Protocol ...............................25 7. The TLS Handshaking Protocols 26
7.2. Alert Protocol ............................................26 7.1. Change Cipher Spec Protocol 27
7.2.1. Closure Alerts .....................................27 7.2. Alert Protocol 27
7.2.2. Error Alerts .......................................28 7.2.1. Closure Alerts 28
7.3. Handshake Protocol Overview ...............................31 7.2.2. Error Alerts 29
7.4. Handshake Protocol ........................................34 7.3. Handshake Protocol Overview 33
7.4.1. Hello Messages .....................................35 7.4. Handshake Protocol 36
7.4.1.1. Hello request .............................35 7.4.1. Hello Messages 37
7.4.1.2. Client Hello ..............................36 7.4.1.1. Hello Request 37
7.4.1.3. Server Hello ..............................39 7.4.1.2. Client Hello 38
7.4.2. Server Certificate .................................40 7.4.1.3. Server Hello 41
7.4.3. Server Key Exchange Message ........................42 7.4.1.4 Hello Extensions 42
7.4.4. Certificate request ................................44 7.4.1.4.1 Signature Algorithms 43
7.4.5. Server Hello Done ..................................46 7.4.2. Server Certificate 45
7.4.6. Client certificate .................................46 7.4.3. Server Key Exchange Message 47
7.4.7. Client Key Exchange Message ........................47 7.4.4. Certificate Request 50
7.4.7.1. RSA Encrypted Premaster Secret Message ....47 7.4.5 Server hello done 51
7.4.7.2. Client Diffie-Hellman Public Value ........50 7.4.6. Client Certificate 52
7.4.8. Certificate verify .................................50 7.4.7. Client Key Exchange Message 54
7.4.9. Finished ...........................................51 7.4.7.1. RSA Encrypted Premaster Secret Message 54
7.4.7.2. Client Diffie-Hellman Public Value 57
8. Cryptographic Computations .....................................52 7.4.8. Certificate verify 58
8.1. Computing the Master Secret ...............................52 7.4.9. Finished 58
8.1.1. RSA ................................................53 8. Cryptographic Computations 60
8.1.2. Diffie-Hellman .....................................53 8.1. Computing the Master Secret 60
9. Mandatory Cipher Suites ........................................53 8.1.1. RSA 61
10. Application Data Protocol .....................................53 8.1.2. Diffie-Hellman 61
11. Security Considerations .......................................53 9. Mandatory Cipher Suites 61
12. IANA Considerations ...........................................54 10. Application Data Protocol 61
A. Appendix - Protocol constant values ............................55 11. Security Considerations 61
A.1. Record layer .........................................55 12. IANA Considerations 61
A.2. Change cipher specs message ..........................56 A. Protocol Constant Values 64
A.3. Alert messages .......................................56 A.1. Record Layer 64
A.4. Handshake protocol ...................................57 A.2. Change Cipher Specs Message 65
A.4.1. Hello messages .....................................57 A.3. Alert Messages 65
A.4.2. Server authentication and key exchange messages ....58 A.4. Handshake Protocol 66
A.4.3. Client authentication and key exchange messages ....59 A.4.1. Hello Messages 66
A.4.4.Handshake finalization message ......................60 A.4.2. Server Authentication and Key Exchange Messages 68
A.5. The CipherSuite ......................................60 A.4.3. Client Authentication and Key Exchange Messages 69
A.6. The Security Parameters ..............................63 A.4.4. Handshake Finalization Message 70
B. Appendix - Glossary ............................................64 A.5. The Cipher Suite 70
C. Appendix - CipherSuite definitions .............................68 A.6. The Security Parameters 72
D. Appendix - Implementation Notes ................................69 A.7. Changes to RFC 4492 73
D.1 Random Number Generation and Seeding ..................70 B. Glossary 73
D.2 Certificates and authentication .......................70 C. Cipher Suite Definitions 78
D.3 CipherSuites ..........................................70 D. Implementation Notes 80
E. Appendix - Backward Compatibility With SSL .....................71 D.1 Random Number Generation and Seeding 80
E.1. Version 2 client hello ...............................72 D.2 Certificates and Authentication 80
E.2. Avoiding man-in-the-middle version rollback ..........74 D.3 Cipher Suites 80
F. Appendix - Security analysis ...................................74 D.4 Implementation Pitfalls 80
F.1. Handshake protocol ...................................74 E. Backward Compatibility 83
F.1.1. Authentication and key exchange ....................74 E.1 Compatibility with TLS 1.0/1.1 and SSL 3.0 83
F.1.1.1. Anonymous key exchange ...........................75 E.2 Compatibility with SSL 2.0 84
F.1.1.2. RSA key exchange and authentication ..............75 E.3. Avoiding Man-in-the-Middle Version Rollback 86
F.1.1.3. Diffie-Hellman key exchange with authentication ..76 F. Security Analysis 87
F.1.2. Version rollback attacks ...........................77 F.1. Handshake Protocol 87
F.1.3. Detecting attacks against the handshake protocol ...77 F.1.1. Authentication and Key Exchange 87
F.1.4. Resuming sessions ..................................78 F.1.1.1. Anonymous Key Exchange 87
F.1.5. MD5 and SHA ........................................78 F.1.1.2. RSA Key Exchange and Authentication 88
F.2. Protecting application data ..........................78 F.1.1.3. Diffie-Hellman Key Exchange with Authentication 88
F.3. Explicit IVs .........................................79 F.1.2. Version Rollback Attacks 89
F.4 Security of Composite Cipher Modes ...................79 F.1.3. Detecting Attacks Against the Handshake Protocol 90
F.5 Denial of Service ....................................80 F.1.4. Resuming Sessions 90
F.6. Final notes ..........................................80 F.2. Protecting Application Data 90
Normative References ..............................................81 F.3. Explicit IVs 91
Informative References ............................................82 F.4. Security of Composite Cipher Modes 91
F.5 Denial of Service 92
F.6 Final Notes 92
1. Introduction 1. Introduction
The primary goal of the TLS Protocol is to provide privacy and data The primary goal of the TLS Protocol is to provide privacy and data
integrity between two communicating applications. The protocol is integrity between two communicating applications. The protocol is
composed of two layers: the TLS Record Protocol and the TLS Handshake composed of two layers: the TLS Record Protocol and the TLS Handshake
Protocol. At the lowest level, layered on top of some reliable Protocol. At the lowest level, layered on top of some reliable
transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol. The transport protocol (e.g., TCP[TCP]), is the TLS Record Protocol. The
TLS Record Protocol provides connection security that has two basic TLS Record Protocol provides connection security that has two basic
properties: properties:
- The connection is private. Symmetric cryptography is used for - The connection is private. Symmetric cryptography is used for
data encryption (e.g., DES [DES], RC4 [SCH] etc.). The keys for data encryption (e.g., DES [DES], RC4 [SCH] etc.). The keys for
this symmetric encryption are generated uniquely for each this symmetric encryption are generated uniquely for each
connection and are based on a secret negotiated by another connection and are based on a secret negotiated by another
protocol (such as the TLS Handshake Protocol). The Record protocol (such as the TLS Handshake Protocol). The Record Protocol
Protocol can also be used without encryption. can also be used without encryption.
- The connection is reliable. Message transport includes a message - The connection is reliable. Message transport includes a message
integrity check using a keyed MAC. Secure hash functions (e.g., integrity check using a keyed MAC. Secure hash functions (e.g.,
SHA, MD5, etc.) are used for MAC computations. The Record SHA, MD5, etc.) are used for MAC computations. The Record Protocol
Protocol can operate without a MAC, but is generally only used in can operate without a MAC, but is generally only used in this mode
this mode while another protocol is using the Record Protocol as a while another protocol is using the Record Protocol as a transport
transport for negotiating security parameters. for negotiating security parameters.
The TLS Record Protocol is used for encapsulation of various higher- The TLS Record Protocol is used for encapsulation of various higher-
level protocols. One such encapsulated protocol, the TLS Handshake level protocols. One such encapsulated protocol, the TLS Handshake
Protocol, allows the server and client to authenticate each other and Protocol, allows the server and client to authenticate each other and
to negotiate an encryption algorithm and cryptographic keys before to negotiate an encryption algorithm and cryptographic keys before
the application protocol transmits or receives its first byte of the application protocol transmits or receives its first byte of
data. The TLS Handshake Protocol provides connection security that data. The TLS Handshake Protocol provides connection security that
has three basic properties: has three basic properties:
- The peer's identity can be authenticated using asymmetric, or - The peer's identity can be authenticated using asymmetric, or
public key, cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This public key, cryptography (e.g., RSA [RSA], DSS [DSS], etc.). This
authentication can be made optional, but is generally required for authentication can be made optional, but is generally required for
at least one of the peers. at least one of the peers.
- The negotiation of a shared secret is secure: the negotiated - The negotiation of a shared secret is secure: the negotiated
secret is unavailable to eavesdroppers, and for any authenticated secret is unavailable to eavesdroppers, and for any authenticated
connection the secret cannot be obtained, even by an attacker who connection the secret cannot be obtained, even by an attacker who
can place himself in the middle of the connection. can place himself in the middle of the connection.
- The negotiation is reliable: no attacker can modify the - The negotiation is reliable: no attacker can modify the
negotiation communication without being detected by the parties to negotiation communication without being detected by the parties to
the communication. the communication.
One advantage of TLS is that it is application protocol independent. One advantage of TLS is that it is application protocol independent.
Higher level protocols can layer on top of the TLS Protocol Higher-level protocols can layer on top of the TLS Protocol
transparently. The TLS standard, however, does not specify how transparently. The TLS standard, however, does not specify how
protocols add security with TLS; the decisions on how to initiate TLS protocols add security with TLS; the decisions on how to initiate TLS
handshaking and how to interpret the authentication certificates handshaking and how to interpret the authentication certificates
exchanged are left to the judgment of the designers and implementors exchanged are left to the judgment of the designers and implementors
of protocols that run on top of TLS. of protocols that run on top of TLS.
1.1. Differences from TLS 1.0 1.1. Requirements Terminology
This document is a revision of the TLS 1.0 [TLS1.0] protocol, and The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
contains some small security improvements, clarifications, and "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
editorial improvements. The major changes are: document are to be interpreted as described in RFC 2119 [REQ].
- The implicit Initialization Vector (IV) is replaced with an 1.2. Major Differences from TLS 1.1
explicit IV to protect against CBC attacks [CBCATT].
- Handling of padding errors is changed to use the bad_record_mac This document is a revision of the TLS 1.1 [TLS1.1] protocol which
alert rather than the decryption_failed alert to protect against contains improved flexibility, particularly for negotiation of
CBC attacks. cryptographic algorithms. The major changes are:
- IANA registries are defined for protocol parameters. - The MD5/SHA-1 combination in the PRF has been replaced with cipher
suite specified PRFs. All cipher suites in this document use
P_SHA256.
- Premature closes no longer cause a session to be nonresumable. - The MD5/SHA-1 combination in the digitally-signed element has been
replaced with a single hash. Signed elements now include a field
that explicitly specifies the hash algorithm used.
- Additional informational notes were added for various new attacks - Substantial cleanup to the clients and servers ability to specify
on TLS. which hash and signature algorithms they will accept. Note that
this also relaxes some of the constraints on signature and hash
algorithms from previous versions of TLS.
In addition, a number of minor clarifications and editorial - Addition of support for authenticated encryption with additional
improvements were made. data modes.
1.2. Requirements Terminology - TLS Extensions definition and AES Cipher Suites were merged in
from external [TLSEXT] and [TLSAES].
In this document, the keywords "MUST", "MUST NOT", "REQUIRED", - Tighter checking of EncryptedPreMasterSecret version numbers.
"SHOULD", "SHOULD NOT" and "MAY" are to be interpreted as described
in RFC 2119 [REQ]. - Tightened up a number of requirements.
- Verify_data length now depends on the cipher suite (default is
still 12).
- Cleaned up description of Bleichenbacher/Klima attack defenses.
- Alerts MUST now be sent in many cases.
- After a certificate_request, if no certificates are available,
clients now MUST send an empty certificate list.
- TLS_RSA_WITH_AES_128_CBC_SHA is now the mandatory to implement
cipher suite.
- Added HMAC-SHA256 cipher suites
- Removed IDEA and DES cipher suites. They are now deprecated and
will be documented in a separate document.
- Support for the SSLv2 backward-compatible hello is now a MAY, not
a SHOULD, with sending it a SHOULD not. Support will probably
become a SHOULD NOT in the future.
- Added limited "fall-through" to the presentation language to allow
multiple case arms to have the same encoding.
- Added an Implementation Pitfalls sections
- The usual clarifications and editorial work.
2. Goals 2. Goals
The goals of TLS Protocol, in order of their priority, are as The goals of TLS Protocol, in order of their priority, are as
follows: follows:
1. Cryptographic security: TLS should be used to establish a secure 1. Cryptographic security: TLS should be used to establish a secure
connection between two parties. connection between two parties.
2. Interoperability: Independent programmers should be able to 2. Interoperability: Independent programmers should be able to
develop applications utilizing TLS that can successfully exchange develop applications utilizing TLS that can successfully exchange
cryptographic parameters without knowledge of one another's code. cryptographic parameters without knowledge of one another's code.
3. Extensibility: TLS seeks to provide a framework into which new 3. Extensibility: TLS seeks to provide a framework into which new
public key and bulk encryption methods can be incorporated as public key and bulk encryption methods can be incorporated as
necessary. This will also accomplish two sub-goals: preventing necessary. This will also accomplish two sub-goals: preventing the
the need to create a new protocol (and risking the introduction of need to create a new protocol (and risking the introduction of
possible new weaknesses) and avoiding the need to implement an possible new weaknesses) and avoiding the need to implement an
entire new security library. entire new security library.
4. Relative efficiency: Cryptographic operations tend to be highly 4. Relative efficiency: Cryptographic operations tend to be highly
CPU intensive, particularly public key operations. For this CPU intensive, particularly public key operations. For this
reason, the TLS protocol has incorporated an optional session reason, the TLS protocol has incorporated an optional session
caching scheme to reduce the number of connections that need to be caching scheme to reduce the number of connections that need to be
established from scratch. Additionally, care has been taken to established from scratch. Additionally, care has been taken to
reduce network activity. reduce network activity.
3. Goals of This Document 3. Goals of This Document
This document and the TLS protocol itself are based on the SSL 3.0 This document and the TLS protocol itself are based on the SSL 3.0
Protocol Specification as published by Netscape. The differences Protocol Specification as published by Netscape. The differences
between this protocol and SSL 3.0 are not dramatic, but they are between this protocol and SSL 3.0 are not dramatic, but they are
significant enough that TLS 1.1, TLS 1.0, and SSL 3.0 do not significant enough that the various versions of TLS and SSL 3.0 do
interoperate (although each protocol incorporates a mechanism by not interoperate (although each protocol incorporates a mechanism by
which an implementation can back down prior versions). This document which an implementation can back down to prior versions). This
is intended primarily for readers who will be implementing the document is intended primarily for readers who will be implementing
protocol and for those doing cryptographic analysis of it. The the protocol and for those doing cryptographic analysis of it. The
specification has been written with this in mind, and it is intended specification has been written with this in mind, and it is intended
to reflect the needs of those two groups. For that reason, many of to reflect the needs of those two groups. For that reason, many of
the algorithm-dependent data structures and rules are included in the the algorithm-dependent data structures and rules are included in the
body of the text (as opposed to in an appendix), providing easier body of the text (as opposed to in an appendix), providing easier
access to them. access to them.
This document is not intended to supply any details of service This document is not intended to supply any details of service
definition or of interface definition, although it does cover select definition or of interface definition, although it does cover select
areas of policy as they are required for the maintenance of solid areas of policy as they are required for the maintenance of solid
security. security.
4. Presentation Language 4. Presentation Language
This document deals with the formatting of data in an external This document deals with the formatting of data in an external
representation. The following very basic and somewhat casually representation. The following very basic and somewhat casually
defined presentation syntax will be used. The syntax draws from defined presentation syntax will be used. The syntax draws from
several sources in its structure. Although it resembles the several sources in its structure. Although it resembles the
programming language "C" in its syntax and XDR [XDR] in both its programming language "C" in its syntax and XDR [XDR] in both its
syntax and intent, it would be risky to draw too many parallels. The syntax and intent, it would be risky to draw too many parallels. The
purpose of this presentation language is to document TLS only; it has purpose of this presentation language is to document TLS only; it has
no general application beyond that particular goal. no general application beyond that particular goal.
4.1. Basic Block Size 4.1. Basic Block Size
The representation of all data items is explicitly specified. The The representation of all data items is explicitly specified. The
basic data block size is one byte (i.e., 8 bits). Multiple byte data basic data block size is one byte (i.e., 8 bits). Multiple byte data
items are concatenations of bytes, from left to right, from top to items are concatenations of bytes, from left to right, from top to
bottom. From the bytestream, a multi-byte item (a numeric in the bottom. From the bytestream, a multi-byte item (a numeric in the
example) is formed (using C notation) by: example) is formed (using C notation) by:
value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) | value = (byte[0] << 8*(n-1)) | (byte[1] << 8*(n-2)) |
... | byte[n-1]; ... | byte[n-1];
This byte ordering for multi-byte values is the commonplace network This byte ordering for multi-byte values is the commonplace network
byte order or big endian format. byte order or big endian format.
4.2. Miscellaneous 4.2. Miscellaneous
Comments begin with "/*" and end with "*/". Comments begin with "/*" and end with "*/".
Optional components are denoted by enclosing them in "[[ ]]" double Optional components are denoted by enclosing them in "[[ ]]" double
brackets. brackets.
Single-byte entities containing uninterpreted data are of type Single-byte entities containing uninterpreted data are of type
opaque. opaque.
4.3. Vectors 4.3. Vectors
skipping to change at page 7, line 32 skipping to change at page 8, line 15
Optional components are denoted by enclosing them in "[[ ]]" double Optional components are denoted by enclosing them in "[[ ]]" double
brackets. brackets.
Single-byte entities containing uninterpreted data are of type Single-byte entities containing uninterpreted data are of type
opaque. opaque.
4.3. Vectors 4.3. Vectors
A vector (single dimensioned array) is a stream of homogeneous data A vector (single dimensioned array) is a stream of homogeneous data
elements. The size of the vector may be specified at documentation elements. The size of the vector may be specified at documentation
time or left unspecified until runtime. In either case, the length time or left unspecified until runtime. In either case, the length
declares the number of bytes, not the number of elements, in the declares the number of bytes, not the number of elements, in the
vector. The syntax for specifying a new type, T', that is a fixed- vector. The syntax for specifying a new type, T', that is a fixed-
length vector of type T is length vector of type T is
T T'[n]; T T'[n];
Here, T' occupies n bytes in the data stream, where n is a multiple Here, T' occupies n bytes in the data stream, where n is a multiple
of the size of T. The length of the vector is not included in the of the size of T. The length of the vector is not included in the
encoded stream. encoded stream.
In the following example, Datum is defined to be three consecutive In the following example, Datum is defined to be three consecutive
bytes that the protocol does not interpret, while Data is three bytes that the protocol does not interpret, while Data is three
consecutive Datum, consuming a total of nine bytes. consecutive Datum, consuming a total of nine bytes.
opaque Datum[3]; /* three uninterpreted bytes */ opaque Datum[3]; /* three uninterpreted bytes */
Datum Data[9]; /* 3 consecutive 3 byte vectors */ Datum Data[9]; /* 3 consecutive 3 byte vectors */
Variable-length vectors are defined by specifying a subrange of legal Variable-length vectors are defined by specifying a subrange of legal
lengths, inclusively, using the notation <floor..ceiling>. When lengths, inclusively, using the notation <floor..ceiling>. When
these are encoded, the actual length precedes the vector's contents these are encoded, the actual length precedes the vector's contents
in the byte stream. The length will be in the form of a number in the byte stream. The length will be in the form of a number
consuming as many bytes as required to hold the vector's specified consuming as many bytes as required to hold the vector's specified
maximum (ceiling) length. A variable-length vector with an actual maximum (ceiling) length. A variable-length vector with an actual
length field of zero is referred to as an empty vector. length field of zero is referred to as an empty vector.
T T'<floor..ceiling>; T T'<floor..ceiling>;
In the following example, mandatory is a vector that must contain In the following example, mandatory is a vector that must contain
between 300 and 400 bytes of type opaque. It can never be empty. between 300 and 400 bytes of type opaque. It can never be empty. The
The actual length field consumes two bytes, a uint16, sufficient to actual length field consumes two bytes, a uint16, sufficient to
represent the value 400 (see Section 4.4). On the other hand, longer represent the value 400 (see Section 4.4). On the other hand, longer
can represent up to 800 bytes of data, or 400 uint16 elements, and it can represent up to 800 bytes of data, or 400 uint16 elements, and it
may be empty. Its encoding will include a two-byte actual length may be empty. Its encoding will include a two-byte actual length
field prepended to the vector. The length of an encoded vector must field prepended to the vector. The length of an encoded vector must
be an even multiple of the length of a single element (for example, a be an even multiple of the length of a single element (for example, a
17-byte vector of uint16 would be illegal). 17-byte vector of uint16 would be illegal).
opaque mandatory<300..400>; opaque mandatory<300..400>;
/* length field is 2 bytes, cannot be empty */ /* length field is 2 bytes, cannot be empty */
uint16 longer<0..800>; uint16 longer<0..800>;
/* zero to 400 16-bit unsigned integers */ /* zero to 400 16-bit unsigned integers */
4.4. Numbers 4.4. Numbers
The basic numeric data type is an unsigned byte (uint8). All larger The basic numeric data type is an unsigned byte (uint8). All larger
numeric data types are formed from fixed-length series of bytes numeric data types are formed from fixed-length series of bytes
concatenated as described in Section 4.1 and are also unsigned. The concatenated as described in Section 4.1 and are also unsigned. The
following numeric types are predefined. following numeric types are predefined.
uint8 uint16[2]; uint8 uint16[2];
uint8 uint24[3]; uint8 uint24[3];
uint8 uint32[4]; uint8 uint32[4];
uint8 uint64[8]; uint8 uint64[8];
All values, here and elsewhere in the specification, are stored in All values, here and elsewhere in the specification, are stored in
"network" or "big-endian" order; the uint32 represented by the hex "network" or "big-endian" order; the uint32 represented by the hex
bytes 01 02 03 04 is equivalent to the decimal value 16909060. bytes 01 02 03 04 is equivalent to the decimal value 16909060.
Note that in some cases (e.g., DH parameters) it is necessary to
represent integers as opaque vectors. In such cases, they are
represented as unsigned integers (i.e., leading zero octets are not
required even if the most significant bit is set).
4.5. Enumerateds 4.5. Enumerateds
An additional sparse data type is available called enum. A field of An additional sparse data type is available called enum. A field of
type enum can only assume the values declared in the definition. type enum can only assume the values declared in the definition.
Each definition is a different type. Only enumerateds of the same Each definition is a different type. Only enumerateds of the same
type may be assigned or compared. Every element of an enumerated type may be assigned or compared. Every element of an enumerated must
must be assigned a value, as demonstrated in the following example. be assigned a value, as demonstrated in the following example. Since
Since the elements of the enumerated are not ordered, they can be the elements of the enumerated are not ordered, they can be assigned
assigned any unique value, in any order. any unique value, in any order.
enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te; enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te;
Enumerateds occupy as much space in the byte stream as would its Enumerateds occupy as much space in the byte stream as would its
maximal defined ordinal value. The following definition would cause maximal defined ordinal value. The following definition would cause
one byte to be used to carry fields of type Color. one byte to be used to carry fields of type Color.
enum { red(3), blue(5), white(7) } Color; enum { red(3), blue(5), white(7) } Color;
One may optionally specify a value without its associated tag to One may optionally specify a value without its associated tag to
force the width definition without defining a superfluous element. force the width definition without defining a superfluous element.
In the following example, Taste will consume two bytes in the data In the following example, Taste will consume two bytes in the data
stream but can only assume the values 1, 2, or 4. stream but can only assume the values 1, 2, or 4.
enum { sweet(1), sour(2), bitter(4), (32000) } Taste; enum { sweet(1), sour(2), bitter(4), (32000) } Taste;
The names of the elements of an enumeration are scoped within the The names of the elements of an enumeration are scoped within the
defined type. In the first example, a fully qualified reference to defined type. In the first example, a fully qualified reference to
the second element of the enumeration would be Color.blue. Such the second element of the enumeration would be Color.blue. Such
qualification is not required if the target of the assignment is well qualification is not required if the target of the assignment is well
specified. specified.
Color color = Color.blue; /* overspecified, legal */ Color color = Color.blue; /* overspecified, legal */
Color color = blue; /* correct, type implicit */ Color color = blue; /* correct, type implicit */
For enumerateds that are never converted to external representation, For enumerateds that are never converted to external representation,
the numerical information may be omitted. the numerical information may be omitted.
enum { low, medium, high } Amount; enum { low, medium, high } Amount;
4.6. Constructed Types 4.6. Constructed Types
Structure types may be constructed from primitive types for Structure types may be constructed from primitive types for
convenience. Each specification declares a new, unique type. The convenience. Each specification declares a new, unique type. The
syntax for definition is much like that of C. syntax for definition is much like that of C.
struct { struct {
T1 f1; T1 f1;
T2 f2; T2 f2;
... ...
Tn fn; Tn fn;
} [[T]]; } [[T]];
The fields within a structure may be qualified using the type's name, The fields within a structure may be qualified using the type's name,
with a syntax much like that available for enumerateds. For example, with a syntax much like that available for enumerateds. For example,
T.f2 refers to the second field of the previous declaration. T.f2 refers to the second field of the previous declaration.
Structure definitions may be embedded. Structure definitions may be embedded.
4.6.1. Variants 4.6.1. Variants
Defined structures may have variants based on some knowledge that is Defined structures may have variants based on some knowledge that is
available within the environment. The selector must be an enumerated available within the environment. The selector must be an enumerated
type that defines the possible variants the structure defines. There type that defines the possible variants the structure defines. There
must be a case arm for every element of the enumeration declared in must be a case arm for every element of the enumeration declared in
the select. The body of the variant structure may be given a label the select. Case arms have limited fall-through: if two case arms
for reference. The mechanism by which the variant is selected at follow in immediate succession with no fields in between, then they
runtime is not prescribed by the presentation language. both contain the same fields. Thus, in the example below, "orange"
and "banana" both contain V2. Note that this is a new piece of syntax
in TLS 1.2.
struct { The body of the variant structure may be given a label for reference.
T1 f1; The mechanism by which the variant is selected at runtime is not
T2 f2; prescribed by the presentation language.
....
Tn fn; struct {
T1 f1;
T2 f2;
....
Tn fn;
select (E) { select (E) {
case e1: Te1; case e1: Te1;
case e2: Te2; case e2: Te2;
case e3: case e4: Te3;
.... ....
case en: Ten; case en: Ten;
} [[fv]]; } [[fv]];
} [[Tv]]; } [[Tv]];
For example: For example:
enum { apple, orange } VariantTag; enum { apple, orange, banana } VariantTag;
struct {
uint16 number;
opaque string<0..10>; /* variable length */
} V1;
struct {
uint32 number;
opaque string[10]; /* fixed length */
} V2;
struct {
select (VariantTag) { /* value of selector is implicit */
case apple: V1; /* VariantBody, tag = apple */
case orange: V2; /* VariantBody, tag = orange */
} variant_body; /* optional label on variant */
} VariantRecord;
Variant structures may be qualified (narrowed) by specifying a value struct {
for the selector prior to the type. For example, an uint16 number;
opaque string<0..10>; /* variable length */
} V1;
orange VariantRecord struct {
uint32 number;
opaque string[10]; /* fixed length */
} V2;
is a narrowed type of a VariantRecord containing a variant_body of struct {
type V2. select (VariantTag) { /* value of selector is implicit */
case apple:
V1; /* VariantBody, tag = apple */
case orange:
case banana:
V2; /* VariantBody, tag = orange or banana */
} variant_body; /* optional label on variant */
} VariantRecord;
4.7. Cryptographic Attributes 4.7. Cryptographic Attributes
The four cryptographic operations digital signing, stream cipher The five cryptographic operations digital signing, stream cipher
encryption, block cipher encryption, and public key encryption are encryption, block cipher encryption, authenticated encryption with
designated digitally-signed, stream-ciphered, block-ciphered, and additional data (AEAD) encryption and public key encryption are
public-key-encrypted, respectively. A field's cryptographic designated digitally-signed, stream-ciphered, block-ciphered, aead-
processing is specified by prepending an appropriate key word ciphered, and public-key-encrypted, respectively. A field's
designation before the field's type specification. Cryptographic cryptographic processing is specified by prepending an appropriate
keys are implied by the current session state (see Section 6.1). key word designation before the field's type specification.
Cryptographic keys are implied by the current session state (see
Section 6.1).
In digital signing, one-way hash functions are used as input for a A digitally-signed element is encoded as a struct DigitallySigned:
signing algorithm. A digitally-signed element is encoded as an
opaque vector <0..2^16-1>, where the length is specified by the
signing algorithm and key.
In RSA signing, a 36-byte structure of two hashes (one SHA and one struct {
MD5) is signed (encrypted with the private key). It is encoded with SignatureAndHashAlgorithm algorithm;
PKCS #1 block type 1, as described in [PKCS1A]. opaque signature<0..2^16-1>;
} DigitallySigned;
Note: The standard reference for PKCS#1 is now RFC 3447 [PKCS1B]. The algorithm field specifies the algorithm used (see Section
However, to minimize differences with TLS 1.0 text, we are 7.4.1.4.1 for the definition of this field.) Note that the
using the terminology of RFC 2313 [PKCS1A]. introduction of the algorithm field is a change from previous
versions. The signature is a digital signature using those
algorithms over the contents of the element. The contents themselves
do not appear on the wire but are simply calculated. The length of
the signature is specified by the signing algorithm and key.
In DSS, the 20 bytes of the SHA hash are run directly through the In RSA signing, the opaque vector contains the signature generated
Digital Signing Algorithm with no additional hashing. This produces using the RSASSA-PKCS1-v1_5 signature scheme defined in [PKCS1]. As
two values, r and s. The DSS signature is an opaque vector, as discussed in [PKCS1], the DigestInfo MUST be DER encoded and for hash
above, the contents of which are the DER encoding of: algorithms without parameters (which include SHA-1) the
DigestInfo.AlgorithmIdentifier.parameters field MUST be NULL but
implementations MUST accept both without parameters and with NULL
parameters. Note that earlier versions of TLS used a different RSA
signature scheme which did not include a DigestInfo encoding.
Dss-Sig-Value ::= SEQUENCE { In DSS, the 20 bytes of the SHA-1 hash are run directly through the
r INTEGER, Digital Signing Algorithm with no additional hashing. This produces
s INTEGER two values, r and s. The DSS signature is an opaque vector, as above,
} the contents of which are the DER encoding of:
Dss-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER
}
Note: In current terminology, DSA refers to the Digital Signature
Algorithm and DSS refers to the NIST standard. For historical
reasons, this document uses DSS and DSA interchangeably
to refer to the DSA algorithm, as was done in SSLv3.
In stream cipher encryption, the plaintext is exclusive-ORed with an In stream cipher encryption, the plaintext is exclusive-ORed with an
identical amount of output generated from a cryptographically secure identical amount of output generated from a cryptographically secure
keyed pseudorandom number generator. keyed pseudorandom number generator.
In block cipher encryption, every block of plaintext encrypts to a In block cipher encryption, every block of plaintext encrypts to a
block of ciphertext. All block cipher encryption is done in CBC block of ciphertext. All block cipher encryption is done in CBC
(Cipher Block Chaining) mode, and all items that are block-ciphered (Cipher Block Chaining) mode, and all items that are block-ciphered
will be an exact multiple of the cipher block length. will be an exact multiple of the cipher block length.
In AEAD encryption, the plaintext is simultaneously encrypted and
integrity protected. The input may be of any length and aead-ciphered
output is generally larger than the input in order to accomodate the
integrity check value.
In public key encryption, a public key algorithm is used to encrypt In public key encryption, a public key algorithm is used to encrypt
data in such a way that it can be decrypted only with the matching data in such a way that it can be decrypted only with the matching
private key. A public-key-encrypted element is encoded as an opaque private key. A public-key-encrypted element is encoded as an opaque
vector <0..2^16-1>, where the length is specified by the signing vector <0..2^16-1>, where the length is specified by the encryption
algorithm and key. algorithm and key.
An RSA-encrypted value is encoded with PKCS #1 block type 2, as RSA encryption is done using the RSAES-PKCS1-v1_5 encryption scheme
described in [PKCS1A]. defined in [PKCS1].
In the following example, In the following example
stream-ciphered struct { stream-ciphered struct {
uint8 field1; uint8 field1;
uint8 field2; uint8 field2;
digitally-signed opaque hash[20]; digitally-signed opaque {
} UserType; uint8 field3<0..255>;
uint8 field4;
};
} UserType;
the contents of hash are used as input for the signing algorithm, and The contents of the inner struct (field3 and field4) are used as
then the entire structure is encrypted with a stream cipher. The input for the signature/hash algorithm, and then the entire structure
length of this structure, in bytes, would be equal to two bytes for is encrypted with a stream cipher. The length of this structure, in
field1 and field2, plus two bytes for the length of the signature, bytes, would be equal to two bytes for field1 and field2, plus two
plus the length of the output of the signing algorithm. This is bytes for the signature and hash algorithm, plus two bytes for the
known because the algorithm and key used for the signing are known length of the signature, plus the length of the output of the signing
prior to encoding or decoding this structure. algorithm. This is known because the algorithm and key used for the
signing are known prior to encoding or decoding this structure.
4.8. Constants 4.8. Constants
Typed constants can be defined for purposes of specification by Typed constants can be defined for purposes of specification by
declaring a symbol of the desired type and assigning values to it. declaring a symbol of the desired type and assigning values to it.
Under-specified types (opaque, variable length vectors, and Under-specified types (opaque, variable length vectors, and
structures that contain opaque) cannot be assigned values. No fields structures that contain opaque) cannot be assigned values. No fields
of a multi-element structure or vector may be elided. of a multi-element structure or vector may be elided.
For example: For example:
struct { struct {
uint8 f1; uint8 f1;
uint8 f2; uint8 f2;
} Example1; } Example1;
Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */ Example1 ex1 = {1, 4}; /* assigns f1 = 1, f2 = 4 */
5. HMAC and the Pseudorandom Function 5. HMAC and the Pseudorandom Function
A number of operations in the TLS record and handshake layer require The TLS record layer uses a keyed Message Authentication Code (MAC)
a keyed MAC; this is a secure digest of some data protected by a to protect message integrity. The cipher suites defined in this
secret. Forging the MAC is infeasible without knowledge of the MAC document use a construction known as HMAC, described in [HMAC], which
secret. The construction we use for this operation is known as HMAC, is based on a hash function. Other cipher suites MAY define their own
and is described in [HMAC]. MAC constructions, if needed.
HMAC can be used with a variety of different hash algorithms. TLS
uses it in the handshake with two different algorithms, MD5 and SHA-
1, denoting these as HMAC_MD5(secret, data) and HMAC_SHA(secret,
data). Additional hash algorithms can be defined by cipher suites
and used to protect record data, but MD5 and SHA-1 are hard coded
into the description of the handshaking for this version of the
protocol.
In addition, a construction is required to do expansion of secrets In addition, a construction is required to do expansion of secrets
into blocks of data for the purposes of key generation or validation. into blocks of data for the purposes of key generation or validation.
This pseudo-random function (PRF) takes as input a secret, a seed, This pseudo-random function (PRF) takes as input a secret, a seed,
and an identifying label and produces an output of arbitrary length. and an identifying label and produces an output of arbitrary length.
In order to make the PRF as secure as possible, it uses two hash In this section, we define one PRF, based on HMAC. This PRF with the
algorithms in a way that should guarantee its security if either SHA-256 hash function is used for all cipher suites defined in this
algorithm remains secure. document and in TLS documents published prior to this document when
TLS 1.2 is negotiated. New cipher suites MUST explicitly specify a
PRF and in general SHOULD use the TLS PRF with SHA-256 or a stronger
standard hash function.
First, we define a data expansion function, P_hash(secret, data) that First, we define a data expansion function, P_hash(secret, data) that
uses a single hash function to expand a secret and seed into an uses a single hash function to expand a secret and seed into an
arbitrary quantity of output: arbitrary quantity of output:
P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) + P_hash(secret, seed) = HMAC_hash(secret, A(1) + seed) +
HMAC_hash(secret, A(2) + seed) + HMAC_hash(secret, A(2) + seed) +
HMAC_hash(secret, A(3) + seed) + ... HMAC_hash(secret, A(3) + seed) + ...
Where + indicates concatenation. Where + indicates concatenation.
A() is defined as: A() is defined as:
A(0) = seed A(0) = seed
A(i) = HMAC_hash(secret, A(i-1)) A(i) = HMAC_hash(secret, A(i-1))
P_hash can be iterated as many times as is necessary to produce the P_hash can be iterated as many times as is necessary to produce the
required quantity of data. For example, if P_SHA-1 is being used to required quantity of data. For example, if P_SHA256 is being used to
create 64 bytes of data, it will have to be iterated 4 times (through create 80 bytes of data, it will have to be iterated three times
A(4)), creating 80 bytes of output data; the last 16 bytes of the (through A(3)), creating 96 bytes of output data; the last 16 bytes
final iteration will then be discarded, leaving 64 bytes of output of the final iteration will then be discarded, leaving 80 bytes of
data. output data.
TLS's PRF is created by splitting the secret into two halves and
using one half to generate data with P_MD5 and the other half to
generate data with P_SHA-1, then exclusive-ORing the outputs of these
two expansion functions together.
S1 and S2 are the two halves of the secret, and each is the same
length. S1 is taken from the first half of the secret, S2 from the
second half. Their length is created by rounding up the length of
the overall secret, divided by two; thus, if the original secret is
an odd number of bytes long, the last byte of S1 will be the same as
the first byte of S2.
L_S = length in bytes of secret;
L_S1 = L_S2 = ceil(L_S / 2);
The secret is partitioned into two halves (with the possibility of
one shared byte) as described above, S1 taking the first L_S1 bytes,
and S2 the last L_S2 bytes.
The PRF is then defined as the result of mixing the two pseudorandom
streams by exclusive-ORing them together.
PRF(secret, label, seed) = P_MD5(S1, label + seed) XOR TLS's PRF is created by applying P_hash to the secret as:
P_SHA-1(S2, label + seed);
The label is an ASCII string. It should be included in the exact PRF(secret, label, seed) = P_<hash>(secret, label + seed)
form it is given without a length byte or trailing null character.
For example, the label "slithy toves" would be processed by hashing
the following bytes:
73 6C 69 74 68 79 20 74 6F 76 65 73 The label is an ASCII string. It should be included in the exact form
it is given without a length byte or trailing null character. For
example, the label "slithy toves" would be processed by hashing the
following bytes:
Note that because MD5 produces 16-byte outputs and SHA-1 produces 73 6C 69 74 68 79 20 74 6F 76 65 73
20-byte outputs, the boundaries of their internal iterations will not
be aligned. Generating an 80-byte output will require that P_MD5
iterate through A(5), while P_SHA-1 will only iterate through A(4).
6. The TLS Record Protocol 6. The TLS Record Protocol
The TLS Record Protocol is a layered protocol. At each layer, The TLS Record Protocol is a layered protocol. At each layer,
messages may include fields for length, description, and content. messages may include fields for length, description, and content.
The Record Protocol takes messages to be transmitted, fragments the The Record Protocol takes messages to be transmitted, fragments the
data into manageable blocks, optionally compresses the data, applies data into manageable blocks, optionally compresses the data, applies
a MAC, encrypts, and transmits the result. Received data is a MAC, encrypts, and transmits the result. Received data is
decrypted, verified, decompressed, reassembled, and then delivered to decrypted, verified, decompressed, reassembled, and then delivered to
higher-level clients. higher-level clients.
Four record protocol clients are described in this document: the Four record protocol clients are described in this document: the
handshake protocol, the alert protocol, the change cipher spec handshake protocol, the alert protocol, the change cipher spec
protocol, and the application data protocol. In order to allow protocol, and the application data protocol. In order to allow
extension of the TLS protocol, additional record types can be extension of the TLS protocol, additional record types can be
supported by the record protocol. Any new record types SHOULD supported by the record protocol. New record type values are assigned
allocate type values immediately beyond the ContentType values for by IANA as described in Section 12.
the four record types described here (see Appendix A.1). All such
values must be defined by RFC 2434 Standards Action. See Section 11
for IANA Considerations for ContentType values.
If a TLS implementation receives a record type it does not Implementations MUST NOT send record types not defined in this
understand, it SHOULD just ignore it. Any protocol designed for use document unless negotiated by some extension. If a TLS
over TLS MUST be carefully designed to deal with all possible attacks implementation receives an unexpected record type, it MUST send an
against it. Note that because the type and length of a record are unexpected_message alert.
not protected by encryption, care SHOULD be taken to minimize the
value of traffic analysis of these values. Any protocol designed for use over TLS MUST be carefully designed to
deal with all possible attacks against it. Note that because the
type and length of a record are not protected by encryption, care
SHOULD be taken to minimize the value of traffic analysis of these
values.
6.1. Connection States 6.1. Connection States
A TLS connection state is the operating environment of the TLS Record A TLS connection state is the operating environment of the TLS Record
Protocol. It specifies a compression algorithm, and encryption Protocol. It specifies a compression algorithm, an encryption
algorithm, and a MAC algorithm. In addition, the parameters for algorithm, and a MAC algorithm. In addition, the parameters for these
these algorithms are known: the MAC secret and the bulk encryption algorithms are known: the MAC key and the bulk encryption keys for
keys for the connection in both the read and the write directions. the connection in both the read and the write directions. Logically,
Logically, there are always four connection states outstanding: the there are always four connection states outstanding: the current read
current read and write states, and the pending read and write states. and write states, and the pending read and write states. All records
All records are processed under the current read and write states. are processed under the current read and write states. The security
The security parameters for the pending states can be set by the TLS parameters for the pending states can be set by the TLS Handshake
Handshake Protocol, and the Change Cipher Spec can selectively make Protocol, and the Change Cipher Spec can selectively make either of
either of the pending states current, in which case the appropriate the pending states current, in which case the appropriate current
current state is disposed of and replaced with the pending state; the state is disposed of and replaced with the pending state; the pending
pending state is then reinitialized to an empty state. It is illegal state is then reinitialized to an empty state. It is illegal to make
to make a state that has not been initialized with security a state that has not been initialized with security parameters a
parameters a current state. The initial current state always current state. The initial current state always specifies that no
specifies that no encryption, compression, or MAC will be used. encryption, compression, or MAC will be used.
The security parameters for a TLS Connection read and write state are The security parameters for a TLS Connection read and write state are
set by providing the following values: set by providing the following values:
connection end connection end
Whether this entity is considered the "client" or the "server" in Whether this entity is considered the "client" or the "server" in
this connection. this connection.
PRF algorithm
An algorithm used to generate keys from the master secret (see
Sections 5 and 6.3).
bulk encryption algorithm bulk encryption algorithm
An algorithm to be used for bulk encryption. This specification An algorithm to be used for bulk encryption. This specification
includes the key size of this algorithm, how much of that key is includes the key size of this algorithm, whether it is a block,
secret, whether it is a block or stream cipher, and the block size stream, or AEAD cipher, the block size of the cipher (if
of the cipher (if appropriate). appropriate), and the lengths of explicit and implicit
initialization vectors (or nonces).
MAC algorithm MAC algorithm
An algorithm to be used for message authentication. This An algorithm to be used for message authentication. This
specification includes the size of the hash returned by the MAC specification includes the size of the value returned by the MAC
algorithm. algorithm.
compression algorithm compression algorithm
An algorithm to be used for data compression. This specification An algorithm to be used for data compression. This specification
must include all information the algorithm requires compression. must include all information the algorithm requires to do
compression.
master secret master secret
A 48-byte secret shared between the two peers in the connection. A 48-byte secret shared between the two peers in the connection.
client random client random
A 32-byte value provided by the client. A 32-byte value provided by the client.
server random server random
A 32-byte value provided by the server. A 32-byte value provided by the server.
These parameters are defined in the presentation language as: These parameters are defined in the presentation language as:
enum { server, client } ConnectionEnd; enum { server, client } ConnectionEnd;
enum { null, rc4, rc2, des, 3des, des40, idea, aes } enum { tls_prf_sha256 } PRFAlgorithm;
BulkCipherAlgorithm;
enum { stream, block } CipherType; enum { null, rc4, 3des, aes }
BulkCipherAlgorithm;
enum { null, md5, sha } MACAlgorithm; enum { stream, block, aead } CipherType;
enum { null(0), (255) } CompressionMethod; enum { null, hmac_md5, hmac_sha, hmac_sha256, hmac_sha384,
hmac_sha512} MACAlgorithm;
/* The algorithms specified in CompressionMethod, /* The use of "sha" above is historical and denotes SHA-1 */
BulkCipherAlgorithm, and MACAlgorithm may be added to. */
struct { enum { null(0), (255) } CompressionMethod;
ConnectionEnd entity;
BulkCipherAlgorithm bulk_cipher_algorithm; /* The algorithms specified in CompressionMethod,
CipherType cipher_type; BulkCipherAlgorithm, and MACAlgorithm may be added to. */
uint8 key_size;
uint8 key_material_length; struct {
MACAlgorithm mac_algorithm; ConnectionEnd entity;
uint8 hash_size; PRFAlgorithm prf_algorithm;
CompressionMethod compression_algorithm; BulkCipherAlgorithm bulk_cipher_algorithm;
opaque master_secret[48]; CipherType cipher_type;
opaque client_random[32]; uint8 enc_key_length;
opaque server_random[32]; uint8 block_length;
} SecurityParameters; uint8 fixed_iv_length;
uint8 record_iv_length;
MACAlgorithm mac_algorithm;
uint8 mac_length;
uint8 mac_key_length;
CompressionMethod compression_algorithm;
opaque master_secret[48];
opaque client_random[32];
opaque server_random[32];
} SecurityParameters;
The record layer will use the security parameters to generate the The record layer will use the security parameters to generate the
following four items: following six items (some of which are not required by all ciphers,
and are thus empty):
client write MAC secret client write MAC key
server write MAC secret server write MAC key
client write key client write encryption key
server write key server write encryption key
client write IV
server write IV
The client write parameters are used by the server when receiving and The client write parameters are used by the server when receiving and
processing records and vice-versa. The algorithm used for generating processing records and vice-versa. The algorithm used for generating
these items from the security parameters is described in Section 6.3. these items from the security parameters is described in Section 6.3.
Once the security parameters have been set and the keys have been Once the security parameters have been set and the keys have been
generated, the connection states can be instantiated by making them generated, the connection states can be instantiated by making them
the current states. These current states MUST be updated for each the current states. These current states MUST be updated for each
record processed. Each connection state includes the following record processed. Each connection state includes the following
elements: elements:
compression state compression state
The current state of the compression algorithm. The current state of the compression algorithm.
cipher state cipher state
The current state of the encryption algorithm. This will consist The current state of the encryption algorithm. This will consist
of the scheduled key for that connection. For stream ciphers, of the scheduled key for that connection. For stream ciphers, this
this will also contain whatever state information is necessary to will also contain whatever state information is necessary to allow
allow the stream to continue to encrypt or decrypt data. the stream to continue to encrypt or decrypt data.
MAC secret MAC key
The MAC secret for this connection, as generated above. The MAC key for this connection, as generated above.
sequence number sequence number
Each connection state contains a sequence number, which is Each connection state contains a sequence number, which is
maintained separately for read and write states. The sequence maintained separately for read and write states. The sequence
number MUST be set to zero whenever a connection state is made the number MUST be set to zero whenever a connection state is made the
active state. Sequence numbers are of type uint64 and may not active state. Sequence numbers are of type uint64 and may not
exceed 2^64-1. Sequence numbers do not wrap. If a TLS exceed 2^64-1. Sequence numbers do not wrap. If a TLS
implementation would need to wrap a sequence number, it must implementation would need to wrap a sequence number, it must
renegotiate instead. A sequence number is incremented after each renegotiate instead. A sequence number is incremented after each
record: specifically, the first record transmitted under a record: specifically, the first record transmitted under a
particular connection state MUST use sequence number 0. particular connection state MUST use sequence number 0.
6.2. Record layer 6.2. Record layer
The TLS Record Layer receives uninterpreted data from higher layers The TLS Record Layer receives uninterpreted data from higher layers
in non-empty blocks of arbitrary size. in non-empty blocks of arbitrary size.
6.2.1. Fragmentation 6.2.1. Fragmentation
The record layer fragments information blocks into TLSPlaintext The record layer fragments information blocks into TLSPlaintext
records carrying data in chunks of 2^14 bytes or less. Client records carrying data in chunks of 2^14 bytes or less. Client message
message boundaries are not preserved in the record layer (i.e., boundaries are not preserved in the record layer (i.e., multiple
multiple client messages of the same ContentType MAY be coalesced client messages of the same ContentType MAY be coalesced into a
into a single TLSPlaintext record, or a single message MAY be single TLSPlaintext record, or a single message MAY be fragmented
fragmented across several records). across several records).
struct { struct {
uint8 major, minor; uint8 major;
} ProtocolVersion; uint8 minor;
} ProtocolVersion;
enum { enum {
change_cipher_spec(20), alert(21), handshake(22), change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255) application_data(23), (255)
} ContentType; } ContentType;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
opaque fragment[TLSPlaintext.length]; opaque fragment[TLSPlaintext.length];
} TLSPlaintext; } TLSPlaintext;
type type
The higher-level protocol used to process the enclosed fragment. The higher-level protocol used to process the enclosed fragment.
version version
The version of the protocol being employed. This document The version of the protocol being employed. This document
describes TLS Version 1.1, which uses the version { 3, 2 }. The describes TLS Version 1.2, which uses the version { 3, 3 }. The
version value 3.2 is historical: TLS version 1.1 is a minor version value 3.3 is historical, deriving from the use of 3.1 for
modification to the TLS 1.0 protocol, which was itself a minor TLS 1.0. (See Appendix A.1). Note that a client that supports
modification to the SSL 3.0 protocol, which bears the version multiple versions of TLS may not know what version will be
value 3.0. (See Appendix A.1.) employed before it receives the ServerHello. See Appendix E for
discussion about what record layer version number should be
employed for ClientHello.
length length
The length (in bytes) of the following TLSPlaintext.fragment. The The length (in bytes) of the following TLSPlaintext.fragment. The
length should not exceed 2^14. length MUST NOT exceed 2^14.
fragment fragment
The application data. This data is transparent and is treated as The application data. This data is transparent and treated as an
an independent block to be dealt with by the higher-level protocol independent block to be dealt with by the higher-level protocol
specified by the type field. specified by the type field.
Implementations MUST NOT send zero-length fragments of Handshake,
Alert, or Change Cipher Spec content types. Zero-length fragments of
Application data MAY be sent as they are potentially useful as a
traffic analysis countermeasure.
Note: Data of different TLS Record layer content types MAY be Note: Data of different TLS Record layer content types MAY be
interleaved. Application data is generally of lower precedence for interleaved. Application data is generally of lower precedence for
transmission than other content types. However, records MUST be transmission than other content types. However, records MUST be
delivered to the network in the same order as they are protected by delivered to the network in the same order as they are protected by
the record layer. Recipients MUST receive and process interleaved the record layer. Recipients MUST receive and process interleaved
application layer traffic during handshakes subsequent to the first application layer traffic during handshakes subsequent to the first
one on a connection. one on a connection.
6.2.2. Record Compression and Decompression 6.2.2. Record Compression and Decompression
All records are compressed using the compression algorithm defined in All records are compressed using the compression algorithm defined in
the current session state. There is always an active compression the current session state. There is always an active compression
algorithm; however, initially it is defined as algorithm; however, initially it is defined as
CompressionMethod.null. The compression algorithm translates a CompressionMethod.null. The compression algorithm translates a
TLSPlaintext structure into a TLSCompressed structure. Compression TLSPlaintext structure into a TLSCompressed structure. Compression
functions are initialized with default state information whenever a functions are initialized with default state information whenever a
connection state is made active. connection state is made active.
Compression must be lossless and may not increase the content length Compression must be lossless and may not increase the content length
by more than 1024 bytes. If the decompression function encounters a by more than 1024 bytes. If the decompression function encounters a
TLSCompressed.fragment that would decompress to a length in excess of TLSCompressed.fragment that would decompress to a length in excess of
2^14 bytes, it should report a fatal decompression failure error. 2^14 bytes, it MUST report a fatal decompression failure error.
struct { struct {
ContentType type; /* same as TLSPlaintext.type */ ContentType type; /* same as TLSPlaintext.type */
ProtocolVersion version;/* same as TLSPlaintext.version */ ProtocolVersion version;/* same as TLSPlaintext.version */
uint16 length; uint16 length;
opaque fragment[TLSCompressed.length]; opaque fragment[TLSCompressed.length];
} TLSCompressed; } TLSCompressed;
length length
The length (in bytes) of the following TLSCompressed.fragment. The length (in bytes) of the following TLSCompressed.fragment.
The length should not exceed 2^14 + 1024. The length MUST NOT exceed 2^14 + 1024.
fragment fragment
The compressed form of TLSPlaintext.fragment. The compressed form of TLSPlaintext.fragment.
Note: A CompressionMethod.null operation is an identity operation; no Note: A CompressionMethod.null operation is an identity operation; no
fields are altered. fields are altered.
Implementation note: Decompression functions are responsible for Implementation note: Decompression functions are responsible for
ensuring that messages cannot cause internal ensuring that messages cannot cause internal buffer overflows.
buffer overflows.
6.2.3. Record Payload Protection 6.2.3. Record Payload Protection
The encryption and MAC functions translate a TLSCompressed structure The encryption and MAC functions translate a TLSCompressed structure
into a TLSCiphertext. The decryption functions reverse the process. into a TLSCiphertext. The decryption functions reverse the process.
The MAC of the record also includes a sequence number so that The MAC of the record also includes a sequence number so that
missing, extra, or repeated messages are detectable. missing, extra, or repeated messages are detectable.
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
select (CipherSpec.cipher_type) { select (SecurityParameters.cipher_type) {
case stream: GenericStreamCipher; case stream: GenericStreamCipher;
case block: GenericBlockCipher; case block: GenericBlockCipher;
} fragment; case aead: GenericAEADCipher;
} TLSCiphertext; } fragment;
} TLSCiphertext;
type type
The type field is identical to TLSCompressed.type. The type field is identical to TLSCompressed.type.
version version
The version field is identical to TLSCompressed.version. The version field is identical to TLSCompressed.version.
length length
The length (in bytes) of the following TLSCiphertext.fragment. The length (in bytes) of the following TLSCiphertext.fragment.
The length may not exceed 2^14 + 2048. The length MUST NOT exceed 2^14 + 2048.
fragment fragment
The encrypted form of TLSCompressed.fragment, with the MAC. The encrypted form of TLSCompressed.fragment, with the MAC.
6.2.3.1. Null or Standard Stream Cipher 6.2.3.1. Null or Standard Stream Cipher
Stream ciphers (including BulkCipherAlgorithm.null, see Appendix A.6) Stream ciphers (including BulkCipherAlgorithm.null, see Appendix A.6)
convert TLSCompressed.fragment structures to and from stream convert TLSCompressed.fragment structures to and from stream
TLSCiphertext.fragment structures. TLSCiphertext.fragment structures.
stream-ciphered struct { stream-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[CipherSpec.hash_size]; opaque MAC[SecurityParameters.mac_length];
} GenericStreamCipher; } GenericStreamCipher;
The MAC is generated as: The MAC is generated as:
HMAC_hash(MAC_write_secret, seq_num + TLSCompressed.type + MAC(MAC_write_key, seq_num +
TLSCompressed.version + TLSCompressed.length + TLSCompressed.type +
TLSCompressed.fragment)); TLSCompressed.version +
TLSCompressed.length +
TLSCompressed.fragment);
where "+" denotes concatenation. where "+" denotes concatenation.
seq_num seq_num
The sequence number for this record. The sequence number for this record.
hash MAC
The hashing algorithm specified by The MAC algorithm specified by SecurityParameters.mac_algorithm.
SecurityParameters.mac_algorithm.
Note that the MAC is computed before encryption. The stream cipher Note that the MAC is computed before encryption. The stream cipher
encrypts the entire block, including the MAC. For stream ciphers encrypts the entire block, including the MAC. For stream ciphers that
that do not use a synchronization vector (such as RC4), the stream do not use a synchronization vector (such as RC4), the stream cipher
cipher state from the end of one record is simply used on the state from the end of one record is simply used on the subsequent
subsequent packet. If the CipherSuite is TLS_NULL_WITH_NULL_NULL, packet. If the cipher suite is TLS_NULL_WITH_NULL_NULL, encryption
encryption consists of the identity operation (i.e., the data is not consists of the identity operation (i.e., the data is not encrypted,
encrypted, and the MAC size is zero, implying that no MAC is used). and the MAC size is zero, implying that no MAC is used).
TLSCiphertext.length is TLSCompressed.length plus TLSCiphertext.length is TLSCompressed.length plus
CipherSpec.hash_size. SecurityParameters.mac_length.
6.2.3.2. CBC Block Cipher 6.2.3.2. CBC Block Cipher
For block ciphers (such as RC2, DES, or AES), the encryption and MAC For block ciphers (such as 3DES, or AES), the encryption and MAC
functions convert TLSCompressed.fragment structures to and from block functions convert TLSCompressed.fragment structures to and from block
TLSCiphertext.fragment structures. TLSCiphertext.fragment structures.
block-ciphered struct { struct {
opaque IV[CipherSpec.block_length]; opaque IV[SecurityParameters.record_iv_length];
opaque content[TLSCompressed.length]; block-ciphered struct {
opaque MAC[CipherSpec.hash_size]; opaque content[TLSCompressed.length];
uint8 padding[GenericBlockCipher.padding_length]; opaque MAC[SecurityParameters.mac_length];
uint8 padding_length; uint8 padding[GenericBlockCipher.padding_length];
} GenericBlockCipher; uint8 padding_length;
};
} GenericBlockCipher;
The MAC is generated as described in Section 6.2.3.1. The MAC is generated as described in Section 6.2.3.1.
IV IV
Unlike previous versions of SSL and TLS, TLS 1.1 uses an explicit The Initialization Vector (IV) SHOULD be chosen at random, and
IV in order to prevent the attacks described by [CBCATT]. We MUST be unpredictable. Note that in versions of TLS prior to 1.1,
recommend the following equivalently strong procedures. For there was no IV field, and the last ciphertext block of the
clarity we use the following notation. previous record (the "CBC residue") was used as the IV. This was
changed to prevent the attacks described in [CBCATT]. For block
IV ciphers, the IV length is of length
The transmitted value of the IV field in the GenericBlockCipher SecurityParameters.record_iv_length which is equal to the
structure. SecurityParameters.block_size.
CBC residue
The last ciphertext block of the previous record.
mask
The actual value that the cipher XORs with the plaintext prior
to encryption of the first cipher block of the record.
In prior versions of TLS, there was no IV field and the CBC
residue and mask were one and the same. See Sections 6.1,
6.2.3.2, and 6.3, of [TLS1.0] for details of TLS 1.0 IV handling.
One of the following two algorithms SHOULD be used to generate the
per-record IV:
(1) Generate a cryptographically strong random string R of length
CipherSpec.block_length. Place R in the IV field. Set the
mask to R. Thus, the first cipher block will be encrypted as
E(R XOR Data).
(2) Generate a cryptographically strong random number R of length
CipherSpec.block_length and prepend it to the plaintext prior
to encryption. In this case either:
(a) The cipher may use a fixed mask such as zero.
(b) The CBC residue from the previous record may be used as
the mask. This preserves maximum code compatibility with
TLS 1.0 and SSL 3. It also has the advantage that it does
not require the ability to quickly reset the IV, which is
known to be a problem on some systems.
In either (2)(a) or (2)(b) the data (R || data) is fed into
the encryption process. The first cipher block (containing
E(mask XOR R) is placed in the IV field. The first block of
content contains E(IV XOR data).
The following alternative procedure MAY be used; however, it has
not been demonstrated to be as cryptographically strong as the
above procedures. The sender prepends a fixed block F to the
plaintext (or, alternatively, a block generated with a weak PRNG).
He then encrypts as in (2), above, using the CBC residue from the
previous block as the mask for the prepended block. Note that in
this case the mask for the first record transmitted by the
application (the Finished) MUST be generated using a
cryptographically strong PRNG.
The decryption operation for all three alternatives is the same.
The receiver decrypts the entire GenericBlockCipher structure and
then discards the first cipher block, corresponding to the IV
component.
padding padding
Padding that is added to force the length of the plaintext to be Padding that is added to force the length of the plaintext to be
an integral multiple of the block cipher's block length. The an integral multiple of the block cipher's block length. The
padding MAY be any length up to 255 bytes, as long as it results padding MAY be any length up to 255 bytes, as long as it results
in the TLSCiphertext.length being an integral multiple of the in the TLSCiphertext.length being an integral multiple of the
block length. Lengths longer than necessary might be desirable to block length. Lengths longer than necessary might be desirable to
frustrate attacks on a protocol that are based on analysis of the frustrate attacks on a protocol that are based on analysis of the
lengths of exchanged messages. Each uint8 in the padding data lengths of exchanged messages. Each uint8 in the padding data
vector MUST be filled with the padding length value. The receiver vector MUST be filled with the padding length value. The receiver
MUST check this padding and SHOULD use the bad_record_mac alert to MUST check this padding and MUST use the bad_record_mac alert to
indicate padding errors. indicate padding errors.
padding_length padding_length
The padding length MUST be such that the total size of the The padding length MUST be such that the total size of the
GenericBlockCipher structure is a multiple of the cipher's block GenericBlockCipher structure is a multiple of the cipher's block
length. Legal values range from zero to 255, inclusive. This length. Legal values range from zero to 255, inclusive. This
length specifies the length of the padding field exclusive of the length specifies the length of the padding field exclusive of the
padding_length field itself. padding_length field itself.
The encrypted data length (TLSCiphertext.length) is one more than the The encrypted data length (TLSCiphertext.length) is one more than the
sum of CipherSpec.block_length, TLSCompressed.length, sum of SecurityParameters.block_length, TLSCompressed.length,
CipherSpec.hash_size, and padding_length. SecurityParameters.mac_length, and padding_length.
Example: If the block length is 8 bytes, the content length Example: If the block length is 8 bytes, the content length
(TLSCompressed.length) is 61 bytes, and the MAC length is 20 (TLSCompressed.length) is 61 bytes, and the MAC length is 20 bytes,
bytes, then the length before padding is 82 bytes (this does then the length before padding is 82 bytes (this does not include the
not include the IV, which may or may not be encrypted, as IV. Thus, the padding length modulo 8 must be equal to 6 in order to
discussed above). Thus, the padding length modulo 8 must be make the total length an even multiple of 8 bytes (the block length).
equal to 6 in order to make the total length an even The padding length can be 6, 14, 22, and so on, through 254. If the
multiple of 8 bytes (the block length). The padding length padding length were the minimum necessary, 6, the padding would be 6
can be 6, 14, 22, and so on, through 254. If the padding bytes, each containing the value 6. Thus, the last 8 octets of the
length were the minimum necessary, 6, the padding would be 6 GenericBlockCipher before block encryption would be xx 06 06 06 06 06
bytes, each containing the value 6. Thus, the last 8 octets 06 06, where xx is the last octet of the MAC.
of the GenericBlockCipher before block encryption would be
xx 06 06 06 06 06 06 06, where xx is the last octet of the
MAC.
Note: With block ciphers in CBC mode (Cipher Block Chaining), it is Note: With block ciphers in CBC mode (Cipher Block Chaining), it is
critical that the entire plaintext of the record be known critical that the entire plaintext of the record be known before any
before any ciphertext is transmitted. Otherwise, it is ciphertext is transmitted. Otherwise, it is possible for the attacker
possible for the attacker to mount the attack described in to mount the attack described in [CBCATT].
[CBCATT].
Implementation Note: Canvel et al. [CBCTIME] have demonstrated a Implementation Note: Canvel et al. [CBCTIME] have demonstrated a
timing attack on CBC padding based on the time timing attack on CBC padding based on the time required to compute
required to compute the MAC. In order to defend the MAC. In order to defend against this attack, implementations MUST
against this attack, implementations MUST ensure ensure that record processing time is essentially the same whether or
that record processing time is essentially the not the padding is correct. In general, the best way to do this is
same whether or not the padding is correct. In to compute the MAC even if the padding is incorrect, and only then
general, the best way to do this is to compute reject the packet. For instance, if the pad appears to be incorrect,
the MAC even if the padding is incorrect, and the implementation might assume a zero-length pad and then compute
only then reject the packet. For instance, if the MAC. This leaves a small timing channel, since MAC performance
the pad appears to be incorrect, the depends to some extent on the size of the data fragment, but it is
implementation might assume a zero-length pad not believed to be large enough to be exploitable, due to the large
and then compute the MAC. This leaves a small block size of existing MACs and the small size of the timing signal.
timing channel, since MAC performance depends to
some extent on the size of the data fragment, 6.2.3.3. AEAD ciphers
but it is not believed to be large enough to be
exploitable, due to the large block size of For AEAD [AEAD] ciphers (such as [CCM] or [GCM]) the AEAD function
existing MACs and the small size of the timing converts TLSCompressed.fragment structures to and from AEAD
signal. TLSCiphertext.fragment structures.
struct {
opaque nonce_explicit[SecurityParameters.record_iv_length];
aead-ciphered struct {
opaque content[TLSCompressed.length];
};
} GenericAEADCipher;
AEAD ciphers take as input a single key, a nonce, a plaintext, and
"additional data" to be included in the authentication check, as
described in Section 2.1 of [AEAD]. The key is either the
client_write_key or the server_write_key. No MAC key is used.
Each AEAD cipher suite MUST specify how the nonce supplied to the
AEAD operation is constructed, and what is the length of the
GenericAEADCipher.nonce_explicit part. In many cases, it is
appropriate to use the partially implicit nonce technique described
in Section 3.2.1 of [AEAD]; with record_iv_length being the length of
the explicit part. In this case, the implicit part SHOULD be derived
from key_block as client_write_iv and server_write_iv (as described
in Section 6.3), and the explicit part is included in
GenericAEAEDCipher.nonce_explicit.
The plaintext is the TLSCompressed.fragment.
The additional authenticated data, which we denote as
additional_data, is defined as follows:
additional_data = seq_num + TLSCompressed.type +
TLSCompressed.version + TLSCompressed.length;
Where "+" denotes concatenation.
The aead_output consists of the ciphertext output by the AEAD
encryption operation. The length will generally be larger than
TLSCompressed.length, but by an amount that varies with the AEAD
cipher. Since the ciphers might incorporate padding, the amount of
overhead could vary with different TLSCompressed.length values. Each
AEAD cipher MUST NOT produce an expansion of greater than 1024 bytes.
Symbolically,
AEADEncrypted = AEAD-Encrypt(key, nonce, plaintext,
additional_data)
In order to decrypt and verify, the cipher takes as input the key,
nonce, the "additional_data", and the AEADEncrypted value. The output
is either the plaintext or an error indicating that the decryption
failed. There is no separate integrity check. I.e.,
TLSCompressed.fragment = AEAD-Decrypt(write_key, nonce,
AEADEncrypted,
additional_data)
If the decryption fails, a fatal bad_record_mac alert MUST be
generated.
6.3. Key Calculation 6.3. Key Calculation
The Record Protocol requires an algorithm to generate keys, and MAC The Record Protocol requires an algorithm to generates keys required
secrets from the security parameters provided by the handshake by the current connection state (see Appendix A.6) from the security
protocol. parameters provided by the handshake protocol.
The master secret is hashed into a sequence of secure bytes, which The master secret is expanded into a sequence of secure bytes, which
are assigned to the MAC secrets and keys required by the current is then split to a client write MAC key, a server write MAC key, a
connection state (see Appendix A.6). CipherSpecs require a client client write encryption key, and a server write encryption key. Each
write MAC secret, a server write MAC secret, a client write key, and of these is generated from the byte sequence in that order. Unused
a server write key, each of which is generated from the master secret values are empty. Some AEAD ciphers may additionally require a
in that order. Unused values are empty. client write IV and a server write IV (see Section 6.2.3.3).
When keys and MAC secrets are generated, the master secret is used as When keys and MAC keys are generated, the master secret is used as an
an entropy source. entropy source.
To generate the key material, compute To generate the key material, compute
key_block = PRF(SecurityParameters.master_secret, key_block = PRF(SecurityParameters.master_secret,
"key expansion", "key expansion",
SecurityParameters.server_random + SecurityParameters.server_random +
SecurityParameters.client_random); SecurityParameters.client_random);
until enough output has been generated. Then the key_block is until enough output has been generated. Then the key_block is
partitioned as follows: partitioned as follows:
client_write_MAC_secret[SecurityParameters.hash_size] client_write_MAC_key[SecurityParameters.mac_key_length]
server_write_MAC_secret[SecurityParameters.hash_size] server_write_MAC_key[SecurityParameters.mac_key_length]
client_write_key[SecurityParameters.key_material_length] client_write_key[SecurityParameters.enc_key_length]
server_write_key[SecurityParameters.key_material_length] server_write_key[SecurityParameters.enc_key_length]
client_write_IV[SecurityParameters.fixed_iv_length]
server_write_IV[SecurityParameters.fixed_iv_length]
Implementation note: The currently defined cipher suite that requires Currently, the client_write_IV and server_write_IV are only generated
the most material is AES_256_CBC_SHA, defined in [TLSAES]. It for implicit nonce techniques as described in Section 3.2.1 of
requires 2 x 32 byte keys, 2 x 20 byte MAC secrets, and 2 x 16 byte [AEAD].
Initialization Vectors, for a total of 136 bytes of key material.
Implementation note: The currently defined cipher suite which
requires the most material is AES_256_CBC_SHA256. It requires 2 x 32
byte keys and 2 x 32 byte MAC keys, for a total 128 bytes of key
material.
7. The TLS Handshaking Protocols 7. The TLS Handshaking Protocols
TLS has three subprotocols that are used to allow peers to agree upon TLS has three subprotocols that are used to allow peers to agree upon
security parameters for the record layer, to authenticate themselves, security parameters for the record layer, to authenticate themselves,
to instantiate negotiated security parameters, and to report error to instantiate negotiated security parameters, and to report error
conditions to each other. conditions to each other.
The Handshake Protocol is responsible for negotiating a session, The Handshake Protocol is responsible for negotiating a session,
which consists of the following items: which consists of the following items:
session identifier session identifier
An arbitrary byte sequence chosen by the server to identify an An arbitrary byte sequence chosen by the server to identify an
active or resumable session state. active or resumable session state.
peer certificate peer certificate
X509v3 [X509] certificate of the peer. This element of the state X509v3 [PKIX] certificate of the peer. This element of the state
may be null. may be null.
compression method compression method
The algorithm used to compress data prior to encryption. The algorithm used to compress data prior to encryption.
cipher spec cipher spec
Specifies the bulk data encryption algorithm (such as null, DES, Specifies the bulk data encryption algorithm (such as null, DES,
etc.) and a MAC algorithm (such as MD5 or SHA). It also defines etc.) and a MAC algorithm (such as MD5 or SHA). It also defines
cryptographic attributes such as the hash_size. (See Appendix A.6 cryptographic attributes such as the mac_length. (See Appendix A.6
for formal definition.) for formal definition.)
master secret master secret
48-byte secret shared between the client and server. 48-byte secret shared between the client and server.
is resumable is resumable
A flag indicating whether the session can be used to initiate new A flag indicating whether the session can be used to initiate new
connections. connections.
These items are then used to create security parameters for use by These items are then used to create security parameters for use by
the Record Layer when protecting application data. Many connections the Record Layer when protecting application data. Many connections
can be instantiated using the same session through the resumption can be instantiated using the same session through the resumption
feature of the TLS Handshake Protocol. feature of the TLS Handshake Protocol.
7.1. Change Cipher Spec Protocol 7.1. Change Cipher Spec Protocol
The change cipher spec protocol exists to signal transitions in The change cipher spec protocol exists to signal transitions in
ciphering strategies. The protocol consists of a single message, ciphering strategies. The protocol consists of a single message,
which is encrypted and compressed under the current (not the pending) which is encrypted and compressed under the current (not the pending)
connection state. The message consists of a single byte of value 1. connection state. The message consists of a single byte of value 1.
struct { struct {
enum { change_cipher_spec(1), (255) } type; enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec; } ChangeCipherSpec;
The change cipher spec message is sent by both the client and the The change cipher spec message is sent by both the client and the
server to notify the receiving party that subsequent records will be server to notify the receiving party that subsequent records will be
protected under the newly negotiated CipherSpec and keys. Reception protected under the newly negotiated CipherSpec and keys. Reception
of this message causes the receiver to instruct the Record Layer to of this message causes the receiver to instruct the Record Layer to
immediately copy the read pending state into the read current state. immediately copy the read pending state into the read current state.
Immediately after sending this message, the sender MUST instruct the Immediately after sending this message, the sender MUST instruct the
record layer to make the write pending state the write active state. record layer to make the write pending state the write active state.
(See Section 6.1.) The change cipher spec message is sent during the (See Section 6.1.) The change cipher spec message is sent during the
handshake after the security parameters have been agreed upon, but handshake after the security parameters have been agreed upon, but
before the verifying finished message is sent (see Section 7.4.9). before the verifying finished message is sent.
Note: If a rehandshake occurs while data is flowing on a connection, Note: If a rehandshake occurs while data is flowing on a connection,
the communicating parties may continue to send data using the the communicating parties may continue to send data using the old
old CipherSpec. However, once the ChangeCipherSpec has been CipherSpec. However, once the ChangeCipherSpec has been sent, the new
sent, the new CipherSpec MUST be used. The first side to send CipherSpec MUST be used. The first side to send the ChangeCipherSpec
the ChangeCipherSpec does not know that the other side has does not know that the other side has finished computing the new
finished computing the new keying material (e.g., if it has to keying material (e.g., if it has to perform a time consuming public
perform a time consuming public key operation). Thus, a small key operation). Thus, a small window of time, during which the
window of time, during which the recipient must buffer the recipient must buffer the data, MAY exist. In practice, with modern
data, MAY exist. In practice, with modern machines this machines this interval is likely to be fairly short.
interval is likely to be fairly short.
7.2. Alert Protocol 7.2. Alert Protocol
One of the content types supported by the TLS Record layer is One of the content types supported by the TLS Record layer is the
the alert type. Alert messages convey the severity of the alert type. Alert messages convey the severity of the message and a
message and a description of the alert. Alert messages with a description of the alert. Alert messages with a level of fatal result
level of fatal result in the immediate termination of the in the immediate termination of the connection. In this case, other
connection. In this case, other connections corresponding to connections corresponding to the session may continue, but the
the session may continue, but the session identifier MUST be session identifier MUST be invalidated, preventing the failed session
invalidated, preventing the failed session from being used to from being used to establish new connections. Like other messages,
establish new connections. Like other messages, alert messages alert messages are encrypted and compressed, as specified by the
are encrypted and compressed, as specified by the current current connection state.
connection state.
enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum { warning(1), fatal(2), (255) } AlertLevel;
close_notify(0), enum {
unexpected_message(10), close_notify(0),
bad_record_mac(20), unexpected_message(10),
decryption_failed(21), bad_record_mac(20),
record_overflow(22), decryption_failed_RESERVED(21),
decompression_failure(30), record_overflow(22),
handshake_failure(40), decompression_failure(30),
no_certificate_RESERVED (41), handshake_failure(40),
bad_certificate(42), no_certificate_RESERVED(41),
unsupported_certificate(43), bad_certificate(42),
certificate_revoked(44), unsupported_certificate(43),
certificate_expired(45), certificate_revoked(44),
certificate_unknown(46), certificate_expired(45),
illegal_parameter(47), certificate_unknown(46),
unknown_ca(48), illegal_parameter(47),
access_denied(49), unknown_ca(48),
decode_error(50), access_denied(49),
decrypt_error(51), decode_error(50),
export_restriction_RESERVED(60), decrypt_error(51),
protocol_version(70), export_restriction_RESERVED(60),
insufficient_security(71), protocol_version(70),
internal_error(80), insufficient_security(71),
user_canceled(90), internal_error(80),
no_renegotiation(100), user_canceled(90),
(255) no_renegotiation(100),
} AlertDescription; unsupported_extension(110),
(255)
} AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
7.2.1. Closure Alerts 7.2.1. Closure Alerts
The client and the server must share knowledge that the connection is The client and the server must share knowledge that the connection is
ending in order to avoid a truncation attack. Either party may ending in order to avoid a truncation attack. Either party may
initiate the exchange of closing messages. initiate the exchange of closing messages.
close_notify close_notify
This message notifies the recipient that the sender will not send This message notifies the recipient that the sender will not send
any more messages on this connection. Note that as of TLS 1.1, any more messages on this connection. Note that as of TLS 1.1,
failure to properly close a connection no longer requires that a failure to properly close a connection no longer requires that a
session not be resumed. This is a change from TLS 1.0 to conform session not be resumed. This is a change from TLS 1.0 to conform
with widespread implementation practice. with widespread implementation practice.
Either party may initiate a close by sending a close_notify alert. Either party may initiate a close by sending a close_notify alert.
Any data received after a closure alert is ignored. Any data received after a closure alert is ignored.
Unless some other fatal alert has been transmitted, each party is Unless some other fatal alert has been transmitted, each party is
required to send a close_notify alert before closing the write side required to send a close_notify alert before closing the write side
of the connection. The other party MUST respond with a close_notify of the connection. The other party MUST respond with a close_notify
alert of its own and close down the connection immediately, alert of its own and close down the connection immediately,
discarding any pending writes. It is not required for the initiator discarding any pending writes. It is not required for the initiator
of the close to wait for the responding close_notify alert before of the close to wait for the responding close_notify alert before
closing the read side of the connection. closing the read side of the connection.
If the application protocol using TLS provides that any data may be If the application protocol using TLS provides that any data may be
carried over the underlying transport after the TLS connection is carried over the underlying transport after the TLS connection is
closed, the TLS implementation must receive the responding closed, the TLS implementation must receive the responding
close_notify alert before indicating to the application layer that close_notify alert before indicating to the application layer that
the TLS connection has ended. If the application protocol will not the TLS connection has ended. If the application protocol will not
transfer any additional data, but will only close the underlying transfer any additional data, but will only close the underlying
transport connection, then the implementation MAY choose to close the transport connection, then the implementation MAY choose to close the
transport without waiting for the responding close_notify. No part transport without waiting for the responding close_notify. No part of
of this standard should be taken to dictate the manner in which a this standard should be taken to dictate the manner in which a usage
usage profile for TLS manages its data transport, including when profile for TLS manages its data transport, including when
connections are opened or closed. connections are opened or closed.
Note: It is assumed that closing a connection reliably delivers Note: It is assumed that closing a connection reliably delivers
pending data before destroying the transport. pending data before destroying the transport.
7.2.2. Error Alerts 7.2.2. Error Alerts
Error handling in the TLS Handshake protocol is very simple. When an Error handling in the TLS Handshake protocol is very simple. When an
error is detected, the detecting party sends a message to the other error is detected, the detecting party sends a message to the other
party. Upon transmission or receipt of a fatal alert message, both party. Upon transmission or receipt of a fatal alert message, both
parties immediately close the connection. Servers and clients MUST parties immediately close the connection. Servers and clients MUST
forget any session-identifiers, keys, and secrets associated with a forget any session-identifiers, keys, and secrets associated with a
failed connection. Thus, any connection terminated with a fatal failed connection. Thus, any connection terminated with a fatal alert
alert MUST NOT be resumed. The following error alerts are defined: MUST NOT be resumed.
Whenever an implementation encounters a condition which is defined as
a fatal alert, it MUST send the appropriate alert prior to closing
the connection. For all errors where an alert level is not explicitly
specified, the sending party MAY determine at its discretion whether
to treat this as a fatal error or not. If the implementation chooses
to send an alert but intends to close the connection immediately
afterwards, it MUST send that alert at the fatal alert level.
If an alert with a level of warning is sent and received, generally
the connection can continue normally. If the receiving party decides
not to proceed with the connection (e.g., after having received a
no_renegotiation alert that it is not willing to accept), it SHOULD
send a fatal alert to terminate the connection. Given this, the
sending party cannot, in general, know how the receiving party will
behave. Therefore, warning alerts are not very useful when the
sending party wants to continue the connection, and thus are
sometimes omitted. For example, if a peer decides to accept an
expired certificate (perhaps after confirming this with the user) and
wants to continue the connection, it would not generally send a
certificate_expired alert.
The following error alerts are defined:
unexpected_message unexpected_message
An inappropriate message was received. This alert is always fatal An inappropriate message was received. This alert is always fatal
and should never be observed in communication between proper and should never be observed in communication between proper
implementations. implementations.
bad_record_mac bad_record_mac
This alert is returned if a record is received with an incorrect This alert is returned if a record is received with an incorrect
MAC. This alert also MUST be returned if an alert is sent because MAC. This alert also MUST be returned if an alert is sent because
a TLSCiphertext decrypted in an invalid way: either it wasn't an a TLSCiphertext decrypted in an invalid way: either it wasn't an
even multiple of the block length, or its padding values, when even multiple of the block length, or its padding values, when
checked, weren't correct. This message is always fatal. checked, weren't correct. This message is always fatal and should
never be observed in communication between proper implementations
decryption_failed (except when messages were corrupted in the network).
This alert MAY be returned if a TLSCiphertext decrypted in an
invalid way: either it wasn't an even multiple of the block
length, or its padding values, when checked, weren't correct.
This message is always fatal.
Note: Differentiating between bad_record_mac and decryption_failed decryption_failed_RESERVED
alerts may permit certain attacks against CBC mode as used in This alert was used in some earlier versions of TLS, and may have
TLS [CBCATT]. It is preferable to uniformly use the permitted certain attacks against the CBC mode [CBCATT]. It MUST
bad_record_mac alert to hide the specific type of the error. NOT be sent by compliant implementations.
record_overflow record_overflow
A TLSCiphertext record was received that had a length more than A TLSCiphertext record was received that had a length more than
2^14+2048 bytes, or a record decrypted to a TLSCompressed 2^14+2048 bytes, or a record decrypted to a TLSCompressed record
record with more than 2^14+1024 bytes. This message is always with more than 2^14+1024 bytes. This message is always fatal and
fatal. should never be observed in communication between proper
implementations (except when messages were corrupted in the
network).
decompression_failure decompression_failure
The decompression function received improper input (e.g., data The decompression function received improper input (e.g., data
that would expand to excessive length). This message is always that would expand to excessive length). This message is always
fatal. fatal and should never be observed in communication between proper
implementations.
handshake_failure handshake_failure
Reception of a handshake_failure alert message indicates that Reception of a handshake_failure alert message indicates that the
the sender was unable to negotiate an acceptable set of sender was unable to negotiate an acceptable set of security
security parameters given the options available. This is a parameters given the options available. This is a fatal error.
fatal error.
no_certificate_RESERVED no_certificate_RESERVED
This alert was used in SSLv3 but not in TLS. It should not be This alert was used in SSLv3 but not any version of TLS. It MUST
sent by compliant implementations. NOT be sent by compliant implementations.
bad_certificate bad_certificate
A certificate was corrupt, contained signatures that did not A certificate was corrupt, contained signatures that did not
verify correctly, etc. verify correctly, etc.
unsupported_certificate unsupported_certificate
A certificate was of an unsupported type. A certificate was of an unsupported type.
certificate_revoked certificate_revoked
A certificate was revoked by its signer. A certificate was revoked by its signer.
certificate_expired certificate_expired
A certificate has expired or is not currently valid. A certificate has expired or is not currently valid.
certificate_unknown certificate_unknown
Some other (unspecified) issue arose in processing the Some other (unspecified) issue arose in processing the
certificate, rendering it unacceptable. certificate, rendering it unacceptable.
illegal_parameter illegal_parameter
A field in the handshake was out of range or inconsistent with A field in the handshake was out of range or inconsistent with
other fields. This is always fatal. other fields. This message is always fatal.
unknown_ca unknown_ca
A valid certificate chain or partial chain was received, but A valid certificate chain or partial chain was received, but the
the certificate was not accepted because the CA certificate certificate was not accepted because the CA certificate could not
could not be located or couldn't be matched with a known, be located or couldn't be matched with a known, trusted CA. This
trusted CA. This message is always fatal. message is always fatal.
access_denied access_denied
A valid certificate was received, but when access control was A valid certificate was received, but when access control was
applied, the sender decided not to proceed with negotiation. applied, the sender decided not to proceed with negotiation. This
This message is always fatal. message is always fatal.
decode_error decode_error
A message could not be decoded because some field was out of A message could not be decoded because some field was out of the
the specified range or the length of the message was incorrect. specified range or the length of the message was incorrect. This
This message is always fatal. message is always fatal and should never be observed in
communication between proper implementations (except when messages
were corrupted in the network).
decrypt_error decrypt_error
A handshake cryptographic operation failed, including being A handshake cryptographic operation failed, including being unable
unable to correctly verify a signature, decrypt a key exchange, to correctly verify a signature or validate a finished message.
or validate a finished message. This message is always fatal.
export_restriction_RESERVED export_restriction_RESERVED
This alert was used in TLS 1.0 but not TLS 1.1. This alert was used in some earlier versions of TLS. It MUST NOT
be sent by compliant implementations.
protocol_version protocol_version
The protocol version the client has attempted to negotiate is The protocol version the client has attempted to negotiate is
recognized but not supported. (For example, old protocol recognized but not supported. (For example, old protocol versions
versions might be avoided for security reasons). This message might be avoided for security reasons). This message is always
is always fatal. fatal.
insufficient_security insufficient_security
Returned instead of handshake_failure when a negotiation has Returned instead of handshake_failure when a negotiation has
failed specifically because the server requires ciphers more failed specifically because the server requires ciphers more
secure than those supported by the client. This message is secure than those supported by the client. This message is always
always fatal. fatal.
internal_error internal_error
An internal error unrelated to the peer or the correctness of An internal error unrelated to the peer or the correctness of the
the protocol (such as a memory allocation failure) makes it protocol (such as a memory allocation failure) makes it impossible
impossible to continue. This message is always fatal. to continue. This message is always fatal.
user_canceled user_canceled
This handshake is being canceled for some reason unrelated to a This handshake is being canceled for some reason unrelated to a
protocol failure. If the user cancels an operation after the protocol failure. If the user cancels an operation after the
handshake is complete, just closing the connection by sending a handshake is complete, just closing the connection by sending a
close_notify is more appropriate. This alert should be close_notify is more appropriate. This alert should be followed by
followed by a close_notify. This message is generally a a close_notify. This message is generally a warning.
warning.
no_renegotiation no_renegotiation
Sent by the client in response to a hello request or by the Sent by the client in response to a hello request or by the server
server in response to a client hello after initial handshaking. in response to a client hello after initial handshaking. Either
Either of these would normally lead to renegotiation; when that of these would normally lead to renegotiation; when that is not
is not appropriate, the recipient should respond with this appropriate, the recipient should respond with this alert. At
alert. At that point, the original requester can decide that point, the original requester can decide whether to proceed
whether to proceed with the connection. One case where this with the connection. One case where this would be appropriate is
would be appropriate is where a server has spawned a process to where a server has spawned a process to satisfy a request; the
satisfy a request; the process might receive security process might receive security parameters (key length,
parameters (key length, authentication, etc.) at startup and it authentication, etc.) at startup and it might be difficult to
might be difficult to communicate changes to these parameters communicate changes to these parameters after that point. This
after that point. This message is always a warning. message is always a warning.
For all errors where an alert level is not explicitly specified, the unsupported_extension
sending party MAY determine at its discretion whether this is a fatal sent by clients that receive an extended server hello containing
error or not; if an alert with a level of warning is received, the an extension that they did not put in the corresponding client
receiving party MAY decide at its discretion whether to treat this as hello. This message is always fatal.
a fatal error or not. However, all messages that are transmitted
with a level of fatal MUST be treated as fatal messages.
New alert values MUST be defined by RFC 2434 Standards Action. See New Alert values are assigned by IANA as described in Section 12.
Section 11 for IANA Considerations for alert values.
7.3. Handshake Protocol Overview 7.3. Handshake Protocol Overview
The cryptographic parameters of the session state are produced by the The cryptographic parameters of the session state are produced by the
TLS Handshake Protocol, which operates on top of the TLS Record TLS Handshake Protocol, which operates on top of the TLS Record
Layer. When a TLS client and server first start communicating, they Layer. When a TLS client and server first start communicating, they
agree on a protocol version, select cryptographic algorithms, agree on a protocol version, select cryptographic algorithms,
optionally authenticate each other, and use public-key encryption optionally authenticate each other, and use public-key encryption
techniques to generate shared secrets. techniques to generate shared secrets.
The TLS Handshake Protocol involves the following steps: The TLS Handshake Protocol involves the following steps:
- Exchange hello messages to agree on algorithms, exchange random - Exchange hello messages to agree on algorithms, exchange random
values, and check for session resumption. values, and check for session resumption.
- Exchange the necessary cryptographic parameters to allow the - Exchange the necessary cryptographic parameters to allow the
skipping to change at page 31, line 48 skipping to change at page 33, line 36
random values. random values.
- Provide security parameters to the record layer. - Provide security parameters to the record layer.
- Allow the client and server to verify that their peer has - Allow the client and server to verify that their peer has
calculated the same security parameters and that the handshake calculated the same security parameters and that the handshake
occurred without tampering by an attacker. occurred without tampering by an attacker.
Note that higher layers should not be overly reliant on whether TLS Note that higher layers should not be overly reliant on whether TLS
always negotiates the strongest possible connection between two always negotiates the strongest possible connection between two
peers. There are a number of ways in which a man-in-the-middle peers. There are a number of ways in which a man in the middle
attacker can attempt to make two entities drop down to the least attacker can attempt to make two entities drop down to the least
secure method they support. The protocol has been designed to secure method they support. The protocol has been designed to
minimize this risk, but there are still attacks available. For minimize this risk, but there are still attacks available: for
example, an attacker could block access to the port a secure service example, an attacker could block access to the port a secure service
runs on, or attempt to get the peers to negotiate an unauthenticated runs on, or attempt to get the peers to negotiate an unauthenticated
connection. The fundamental rule is that higher levels must be connection. The fundamental rule is that higher levels must be
cognizant of what their security requirements are and never transmit cognizant of what their security requirements are and never transmit
information over a channel less secure than what they require. The information over a channel less secure than what they require. The
TLS protocol is secure in that any cipher suite offers its promised TLS protocol is secure in that any cipher suite offers its promised
level of security: if you negotiate 3DES with a 1024 bit RSA key level of security: if you negotiate 3DES with a 1024 bit RSA key
exchange with a host whose certificate you have verified, you can exchange with a host whose certificate you have verified, you can
expect to be that secure. expect to be that secure.
However, one SHOULD never send data over a link encrypted with 40-bit
security unless one feels that data is worth no more than the effort
required to break that encryption.
These goals are achieved by the handshake protocol, which can be These goals are achieved by the handshake protocol, which can be
summarized as follows: The client sends a client hello message to summarized as follows: The client sends a client hello message to
which the server must respond with a server hello message, or else a which the server must respond with a server hello message, or else a
fatal error will occur and the connection will fail. The client fatal error will occur and the connection will fail. The client hello
hello and server hello are used to establish security enhancement and server hello are used to establish security enhancement
capabilities between client and server. The client hello and server capabilities between client and server. The client hello and server
hello establish the following attributes: Protocol Version, Session hello establish the following attributes: Protocol Version, Session
ID, Cipher Suite, and Compression Method. Additionally, two random ID, Cipher Suite, and Compression Method. Additionally, two random
values are generated and exchanged: ClientHello.random and values are generated and exchanged: ClientHello.random and
ServerHello.random. ServerHello.random.
The actual key exchange uses up to four messages: the server The actual key exchange uses up to four messages: the server
certificate, the server key exchange, the client certificate, and the certificate, the server key exchange, the client certificate, and the
client key exchange. New key exchange methods can be created by client key exchange. New key exchange methods can be created by
specifying a format for these messages and by defining the use of the specifying a format for these messages and by defining the use of the
messages to allow the client and server to agree upon a shared messages to allow the client and server to agree upon a shared
secret. This secret MUST be quite long; currently defined key secret. This secret MUST be quite long; currently defined key
exchange methods exchange secrets that range from 48 to 128 bytes in exchange methods exchange secrets that range from 46 bytes upwards.
length.
Following the hello messages, the server will send its certificate, Following the hello messages, the server will send its certificate,
if it is to be authenticated. Additionally, a server key exchange if it is to be authenticated. Additionally, a server key exchange
message may be sent, if it is required (e.g., if the server has no message may be sent, if it is required (e.g., if their server has no
certificate, or if its certificate is for signing only). If the certificate, or if its certificate is for signing only). If the
server is authenticated, it may request a certificate from the server is authenticated, it may request a certificate from the
client, if that is appropriate to the cipher suite selected. Next, client, if that is appropriate to the cipher suite selected. Next,
the server will send the server hello done message, indicating that the server will send the server hello done message, indicating that
the hello-message phase of the handshake is complete. The server the hello-message phase of the handshake is complete. The server will
will then wait for a client response. If the server has sent a then wait for a client response. If the server has sent a certificate
certificate request message, the client must send the certificate request message, the client MUST send the certificate message. The
message. The client key exchange message is now sent, and the client key exchange message is now sent, and the content of that
content of that message will depend on the public key algorithm message will depend on the public key algorithm selected between the
selected between the client hello and the server hello. If the client hello and the server hello. If the client has sent a
client has sent a certificate with signing ability, a digitally- certificate with signing ability, a digitally-signed certificate
signed certificate verify message is sent to explicitly verify the verify message is sent to explicitly verify possession of the private
certificate. key in the certificate.
At this point, a change cipher spec message is sent by the client, At this point, a change cipher spec message is sent by the client,
and the client copies the pending Cipher Spec into the current Cipher and the client copies the pending Cipher Spec into the current Cipher
Spec. The client then immediately sends the finished message under Spec. The client then immediately sends the finished message under
the new algorithms, keys, and secrets. In response, the server will the new algorithms, keys, and secrets. In response, the server will
send its own change cipher spec message, transfer the pending to the send its own change cipher spec message, transfer the pending to the
current Cipher Spec, and send its finished message under the new current Cipher Spec, and send its finished message under the new
Cipher Spec. At this point, the handshake is complete, and the Cipher Spec. At this point, the handshake is complete, and the client
client and server may begin to exchange application layer data. (See and server may begin to exchange application layer data. (See flow
flow chart below.) Application data MUST NOT be sent prior to the chart below.) Application data MUST NOT be sent prior to the
completion of the first handshake (before a cipher suite other completion of the first handshake (before a cipher suite other than
TLS_NULL_WITH_NULL_NULL is established). TLS_NULL_WITH_NULL_NULL is established).
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
Certificate* Certificate*
ServerKeyExchange* ServerKeyExchange*
CertificateRequest* CertificateRequest*
<-------- ServerHelloDone <-------- ServerHelloDone
skipping to change at page 33, line 38 skipping to change at page 35, line 20
ClientKeyExchange ClientKeyExchange
CertificateVerify* CertificateVerify*
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
Application Data <-------> Application Data Application Data <-------> Application Data
Fig. 1. Message flow for a full handshake Fig. 1. Message flow for a full handshake
* Indicates optional or situation-dependent messages that are not * Indicates optional or situation-dependent messages that are not
always sent. always sent.
Note: To help avoid pipeline stalls, ChangeCipherSpec is an Note: To help avoid pipeline stalls, ChangeCipherSpec is an
independent TLS Protocol content type, and is not actually a independent TLS Protocol content type, and is not actually a TLS
TLS handshake message. handshake message.
When the client and server decide to resume a previous session or When the client and server decide to resume a previous session or
duplicate an existing session (instead of negotiating new security duplicate an existing session (instead of negotiating new security
parameters), the message flow is as follows: parameters), the message flow is as follows:
The client sends a ClientHello using the Session ID of the session to The client sends a ClientHello using the Session ID of the session to
be resumed. The server then checks its session cache for a match. be resumed. The server then checks its session cache for a match. If
a match is found, and the server is willing to re-establish the
If a match is found, and the server is willing to re-establish the
connection under the specified session state, it will send a connection under the specified session state, it will send a
ServerHello with the same Session ID value. At this point, both ServerHello with the same Session ID value. At this point, both
client and server MUST send change cipher spec messages and proceed client and server MUST send change cipher spec messages and proceed
directly to finished messages. Once the re-establishment is directly to finished messages. Once the re-establishment is complete,
complete, the client and server MAY begin to exchange application the client and server MAY begin to exchange application layer data.
layer data. (See flow chart below.) If a Session ID match is not (See flow chart below.) If a Session ID match is not found, the
found, the server generates a new session ID and the TLS client and server generates a new session ID and the TLS client and server
server perform a full handshake. perform a full handshake.
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
Application Data <-------> Application Data Application Data <-------> Application Data
skipping to change at page 34, line 24 skipping to change at page 36, line 4
Client Server Client Server
ClientHello --------> ClientHello -------->
ServerHello ServerHello
[ChangeCipherSpec] [ChangeCipherSpec]
<-------- Finished <-------- Finished
[ChangeCipherSpec] [ChangeCipherSpec]
Finished --------> Finished -------->
Application Data <-------> Application Data Application Data <-------> Application Data
Fig. 2. Message flow for an abbreviated handshake Fig. 2. Message flow for an abbreviated handshake
The contents and significance of each message will be presented in The contents and significance of each message will be presented in
detail in the following sections. detail in the following sections.
7.4. Handshake Protocol 7.4. Handshake Protocol
The TLS Handshake Protocol is one of the defined higher-level clients The TLS Handshake Protocol is one of the defined higher-level clients
of the TLS Record Protocol. This protocol is used to negotiate the of the TLS Record Protocol. This protocol is used to negotiate the
secure attributes of a session. Handshake messages are supplied to secure attributes of a session. Handshake messages are supplied to
the TLS Record Layer, where they are encapsulated within one or more the TLS Record Layer, where they are encapsulated within one or more
TLSPlaintext structures, which are processed and transmitted as TLSPlaintext structures, which are processed and transmitted as
specified by the current active session state. specified by the current active session state.
enum { enum {
hello_request(0), client_hello(1), server_hello(2), hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12), certificate(11), server_key_exchange (12),
certificate_request(13), server_hello_done(14), certificate_request(13), server_hello_done(14),
certificate_verify(15), client_key_exchange(16), certificate_verify(15), client_key_exchange(16),
finished(20), (255) finished(20), (255)
skipping to change at page 35, line 17 skipping to change at page 36, line 45
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case server_hello_done: ServerHelloDone; case server_hello_done: ServerHelloDone;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange; case client_key_exchange: ClientKeyExchange;
case finished: Finished; case finished: Finished;
} body; } body;
} Handshake; } Handshake;
The handshake protocol messages are presented below in the order they The handshake protocol messages are presented below in the order they
MUST be sent; sending handshake messages in an unexpected order MUST be sent; sending handshake messages in an unexpected order
results in a fatal error. Unneeded handshake messages can be results in a fatal error. Unneeded handshake messages can be omitted,
omitted, however. Note one exception to the ordering: the however. Note one exception to the ordering: the Certificate message
Certificate message is used twice in the handshake (from server to is used twice in the handshake (from server to client, then from
client, then from client to server), but is described only in its client to server), but described only in its first position. The one
first position. The one message that is not bound by these ordering message that is not bound by these ordering rules is the Hello
rules is the Hello Request message, which can be sent at any time, Request message, which can be sent at any time, but which SHOULD be
but which should be ignored by the client if it arrives in the middle ignored by the client if it arrives in the middle of a handshake.
of a handshake.
New Handshake message type values MUST be defined via RFC 2434 New Handshake message types are assigned by IANA as described in
Standards Action. See Section 11 for IANA Considerations for these Section 12.
values.
7.4.1. Hello Messages 7.4.1. Hello Messages
The hello phase messages are used to exchange security enhancement The hello phase messages are used to exchange security enhancement
capabilities between the client and server. When a new session capabilities between the client and server. When a new session
begins, the Record Layer's connection state encryption, hash, and begins, the Record Layer's connection state encryption, hash, and
compression algorithms are initialized to null. The current compression algorithms are initialized to null. The current
connection state is used for renegotiation messages. connection state is used for renegotiation messages.
7.4.1.1. Hello request 7.4.1.1. Hello Request
When this message will be sent: When this message will be sent:
The hello request message MAY be sent by the server at any time. The hello request message MAY be sent by the server at any time.
Meaning of this message: Meaning of this message:
Hello request is a simple notification that the client should Hello request is a simple notification that the client should
begin the negotiation process anew by sending a client hello begin the negotiation process anew by sending a client hello
message when convenient. This message will be ignored by the message when convenient. This message is not intended to establish
client if the client is currently negotiating a session. This which side is the client or server but merely to initiate a new
message may be ignored by the client if it does not wish to negotiation. Servers SHOULD NOT send a HelloRequest immediately
renegotiate a session, or the client may, if it wishes, respond upon the client's initial connection. It is the client's job to
with a no_renegotiation alert. Since handshake messages are send a ClientHello at that time.
intended to have transmission precedence over application data, it
is expected that the negotiation will begin before no more than a
few records are received from the client. If the server sends a
hello request but does not receive a client hello in response, it
may close the connection with a fatal alert.
After sending a hello request, servers SHOULD not repeat the This message will be ignored by the client if the client is
currently negotiating a session. This message may be ignored by
the client if it does not wish to renegotiate a session, or the
client may, if it wishes, respond with a no_renegotiation alert.
Since handshake messages are intended to have transmission
precedence over application data, it is expected that the
negotiation will begin before no more than a few records are
received from the client. If the server sends a hello request but
does not receive a client hello in response, it may close the
connection with a fatal alert.
After sending a hello request, servers SHOULD NOT repeat the
request until the subsequent handshake negotiation is complete. request until the subsequent handshake negotiation is complete.
Structure of this message: Structure of this message:
struct { } HelloRequest; struct { } HelloRequest;
Note: This message MUST NOT be included in the message hashes that Note: This message MUST NOT be included in the message hashes that
are maintained throughout the handshake and used in the are maintained throughout the handshake and used in the finished
finished messages and the certificate verify message. messages and the certificate verify message.
7.4.1.2. Client Hello 7.4.1.2. Client Hello
When this message will be sent: When this message will be sent:
When a client first connects to a server it is required to send When a client first connects to a server it is required to send
the client hello as its first message. The client can also send a the client hello as its first message. The client can also send a
client hello in response to a hello request or on its own client hello in response to a hello request or on its own
initiative in order to renegotiate the security parameters in an initiative in order to renegotiate the security parameters in an
existing connection. existing connection.
Structure of this message: Structure of this message:
The client hello message includes a random structure, which is The client hello message includes a random structure, which is
used later in the protocol. used later in the protocol.
struct { struct {
uint32 gmt_unix_time; uint32 gmt_unix_time;
opaque random_bytes[28]; opaque random_bytes[28];
} Random; } Random;
gmt_unix_time The current time and date in standard UNIX 32-bit gmt_unix_time
format (seconds since the midnight starting Jan 1, 1970, GMT, The current time and date in standard UNIX 32-bit format
ignoring leap seconds) according to the sender's internal clock. (seconds since the midnight starting Jan 1, 1970, GMT, ignoring
Clocks are not required to be set correctly by the basic TLS leap seconds) according to the sender's internal clock. Clocks
Protocol; higher-level or application protocols may define are not required to be set correctly by the basic TLS Protocol;
additional requirements. higher-level or application protocols may define additional
requirements.
random_bytes random_bytes
28 bytes generated by a secure random number generator. 28 bytes generated by a secure random number generator.
The client hello message includes a variable-length session The client hello message includes a variable-length session
identifier. If not empty, the value identifies a session between the identifier. If not empty, the value identifies a session between the
same client and server whose security parameters the client wishes to same client and server whose security parameters the client wishes to
reuse. The session identifier MAY be from an earlier connection, reuse. The session identifier MAY be from an earlier connection, this
from this connection, or from another currently active connection. connection, or from another currently active connection. The second
The second option is useful if the client only wishes to update the option is useful if the client only wishes to update the random
random structures and derived values of a connection, and the third structures and derived values of a connection, and the third option
option makes it possible to establish several independent secure makes it possible to establish several independent secure connections
connections without repeating the full handshake protocol. These without repeating the full handshake protocol. These independent
independent connections may occur sequentially or simultaneously; a connections may occur sequentially or simultaneously; a SessionID
SessionID becomes valid when the handshake negotiating it completes becomes valid when the handshake negotiating it completes with the
with the exchange of Finished messages and persists until it is exchange of Finished messages and persists until it is removed due to
removed due to aging or because a fatal error was encountered on a aging or because a fatal error was encountered on a connection
connection associated with the session. The actual contents of the associated with the session. The actual contents of the SessionID are
SessionID are defined by the server. defined by the server.
opaque SessionID<0..32>; opaque SessionID<0..32>;
Warning: Because the SessionID is transmitted without encryption or Warning: Because the SessionID is transmitted without encryption or
immediate MAC protection, servers MUST not place immediate MAC protection, servers MUST NOT place confidential
confidential information in session identifiers or let the information in session identifiers or let the contents of fake
contents of fake session identifiers cause any breach of session identifiers cause any breach of security. (Note that the
security. (Note that the content of the handshake as a content of the handshake as a whole, including the SessionID, is
whole, including the SessionID, is protected by the Finished protected by the Finished messages exchanged at the end of the
messages exchanged at the end of the handshake.) handshake.)
The CipherSuite list, passed from the client to the server in the The cipher suite list, passed from the client to the server in the
client hello message, contains the combinations of cryptographic client hello message, contains the combinations of cryptographic
algorithms supported by the client in order of the client's algorithms supported by the client in order of the client's
preference (favorite choice first). Each CipherSuite defines a key preference (favorite choice first). Each cipher suite defines a key
exchange algorithm, a bulk encryption algorithm (including secret key exchange algorithm, a bulk encryption algorithm (including secret key
length), and a MAC algorithm. The server will select a cipher suite length), a MAC algorithm, and a PRF. The server will select a cipher
or, if no acceptable choices are presented, return a handshake suite or, if no acceptable choices are presented, return a handshake
failure alert and close the connection. failure alert and close the connection. If the list contains cipher
suites the server does not recognize, support, or wish to use, the
server MUST ignore those cipher suites, and process the remaining
ones as usual.
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
The client hello includes a list of compression algorithms supported The client hello includes a list of compression algorithms supported
by the client, ordered according to the client's preference. by the client, ordered according to the client's preference.
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suites<2..2^16-1>; CipherSuite cipher_suites<2..2^16-2>;
CompressionMethod compression_methods<1..2^8-1>; CompressionMethod compression_methods<1..2^8-1>;
select (extensions_present) {
case false:
struct {};
case true:
Extension extensions<0..2^16-1>;
};
} ClientHello; } ClientHello;
TLS allows extensions to follow the compression_methods field in an
extensions block. The presence of extensions can be detected by
determining whether there are bytes following the compression_methods
at the end of the ClientHello. Note that this method of detecting
optional data differs from the normal TLS method of having a
variable-length field but is used for compatibility with TLS before
extensions were defined.
client_version client_version
The version of the TLS protocol by which the client wishes to The version of the TLS protocol by which the client wishes to
communicate during this session. This SHOULD be the latest communicate during this session. This SHOULD be the latest
(highest valued) version supported by the client. For this (highest valued) version supported by the client. For this version
version of the specification, the version will be 3.2. (See of the specification, the version will be 3.3 (See Appendix E for
Appendix E for details about backward compatibility.) details about backward compatibility).
random random
A client-generated random structure. A client-generated random structure.
session_id session_id
The ID of a session the client wishes to use for this connection. The ID of a session the client wishes to use for this connection.
This field should be empty if no session_id is available or if the This field is empty if no session_id is available, or it the
client wishes to generate new security parameters. client wishes to generate new security parameters.
cipher_suites cipher_suites
This is a list of the cryptographic options supported by the This is a list of the cryptographic options supported by the
client, with the client's first preference first. If the client, with the client's first preference first. If the
session_id field is not empty (implying a session resumption session_id field is not empty (implying a session resumption
request) this vector MUST include at least the cipher_suite from request) this vector MUST include at least the cipher_suite from
that session. Values are defined in Appendix A.5. that session. Values are defined in Appendix A.5.
compression_methods compression_methods
This is a list of the compression methods supported by the client, This is a list of the compression methods supported by the client,
sorted by client preference. If the session_id field is not empty sorted by client preference. If the session_id field is not empty
(implying a session resumption request) it MUST include the (implying a session resumption request) it MUST include the
compression_method from that session. This vector MUST contain, compression_method from that session. This vector MUST contain,
and all implementations MUST support, CompressionMethod.null. and all implementations MUST support, CompressionMethod.null.
Thus, a client and server will always be able to agree on a Thus, a client and server will always be able to agree on a
compression method. compression method.
After sending the client hello message, the client waits for a server extensions
hello message. Any other handshake message returned by the server Clients MAY request extended functionality from servers by sending
except for a hello request is treated as a fatal error. data in the extensions Here the new "extensions" field contains a
list of extensions. The actual "Extension" format is defined in
Section 7.4.1.4.
Forward compatibility note: In the interests of forward In the event that a client requests additional functionality using
compatibility, it is permitted that a client hello message include extensions, and this functionality is not supplied by the server, the
extra data after the compression methods. This data MUST be included client MAY abort the handshake. A server MUST accept client hello
in the handshake hashes, but must otherwise be ignored. This is the messages both with and without the extensions field, and (as for all
only handshake message for which this is legal; for all other other messages) MUST check that the amount of data in the message
messages, the amount of data in the message MUST match the precisely matches one of these formats; if not, then it MUST send a
description of the message precisely. fatal "decode_error" alert.
Note: For the intended use of trailing data in the ClientHello, After sending the client hello message, the client waits for a server
see RFC 3546 [TLSEXT]. hello message. Any other handshake message returned by the server
except for a hello request is treated as a fatal error.
7.4.1.3. Server Hello 7.4.1.3. Server Hello
The server will send this message in response to a client hello When this message will be sent:
message when it was able to find an acceptable set of algorithms. If
it cannot find such a match, it will respond with a handshake failure The server will send this message in response to a client hello
alert. message when it was able to find an acceptable set of algorithms.
If it cannot find such a match, it will respond with a handshake
failure alert.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suite; CipherSuite cipher_suite;
CompressionMethod compression_method; CompressionMethod compression_method;
} ServerHello; select (extensions_present) {
case false:
struct {};
case true:
Extension extensions<0..2^16-1>;
};
} ServerHello;
The presence of extensions can be detected by determining whether
there are bytes following the compression_method field at the end of
the ServerHello.
server_version server_version
This field will contain the lower of that suggested by the client This field will contain the lower of that suggested by the client
in the client hello and the highest supported by the server. For in the client hello and the highest supported by the server. For
this version of the specification, the version is 3.2. (See this version of the specification, the version is 3.3. (See
Appendix E for details about backward compatibility.) Appendix E for details about backward compatibility.)
random random
This structure is generated by the server and MUST be This structure is generated by the server and MUST be
independently generated from the ClientHello.random. independently generated from the ClientHello.random.
session_id session_id
This is the identity of the session corresponding to this This is the identity of the session corresponding to this
connection. If the ClientHello.session_id was non-empty, the connection. If the ClientHello.session_id was non-empty, the
server will look in its session cache for a match. If a match is server will look in its session cache for a match. If a match is
found and the server is willing to establish the new connection found and the server is willing to establish the new connection
using the specified session state, the server will respond with using the specified session state, the server will respond with
the same value as was supplied by the client. This indicates a the same value as was supplied by the client. This indicates a
resumed session and dictates that the parties must proceed resumed session and dictates that the parties must proceed
directly to the finished messages. Otherwise this field will directly to the finished messages. Otherwise this field will
contain a different value identifying the new session. The server contain a different value identifying the new session. The server
may return an empty session_id to indicate that the session will may return an empty session_id to indicate that the session will
not be cached and therefore cannot be resumed. If a session is not be cached and therefore cannot be resumed. If a session is
resumed, it must be resumed using the same cipher suite it was resumed, it must be resumed using the same cipher suite it was
originally negotiated with. originally negotiated with. Note that there is no requirement that
the server resume any session even if it had formerly provided a
session_id. Client MUST be prepared to do a full negotiation --
including negotiating new cipher suites -- during any handshake.
cipher_suite cipher_suite
The single cipher suite selected by the server from the list in The single cipher suite selected by the server from the list in
ClientHello.cipher_suites. For resumed sessions, this field is ClientHello.cipher_suites. For resumed sessions, this field is the
the value from the state of the session being resumed. value from the state of the session being resumed.
compression_method The single compression algorithm selected by the compression_method
server from the list in ClientHello.compression_methods. For The single compression algorithm selected by the server from the
resumed sessions this field is the value from the resumed session list in ClientHello.compression_methods. For resumed sessions this
state. field is the value from the resumed session state.
7.4.2. Server Certificate extensions
A list of extensions. Note that only extensions offered by the
client can appear in the server's list.
When this message will be sent: 7.4.1.4 Hello Extensions
The server MUST send a certificate whenever the agreed-upon key The extension format is:
exchange method is not an anonymous one. This message will always
immediately follow the server hello message.
Meaning of this message: struct {
ExtensionType extension_type;
opaque extension_data<0..2^16-1>;
} Extension;
The certificate type MUST be appropriate for the selected cipher enum {
suite's key exchange algorithm, and is generally an X.509v3 signature_algorithms(TBD-BY-IANA), (65535)
certificate. It MUST contain a key that matches the key exchange } ExtensionType;
method, as follows. Unless otherwise specified, the signing
algorithm for the certificate MUST be the same as the algorithm
for the certificate key. Unless otherwise specified, the public
key MAY be of any length.
Key Exchange Algorithm Certificate Key Type Here:
RSA RSA public key; the certificate MUST - "extension_type" identifies the particular extension type.
allow the key to be used for encryption.
DHE_DSS DSS public key. - "extension_data" contains information specific to the particular
extension type.
DHE_RSA RSA public key that can be used for The initial set of extensions is defined in a companion document
signing. [TLSEXT]. The list of extension types is maintained by IANA as
described in Section 12.
DH_DSS Diffie-Hellman key. The algorithm used There are subtle (and not so subtle) interactions that may occur in
to sign the certificate MUST be DSS. this protocol between new features and existing features which may
result in a significant reduction in overall security, The following
considerations should be taken into account when designing new
extensions:
DH_RSA Diffie-Hellman key. The algorithm used - Some cases where a server does not agree to an extension are error
to sign the certificate MUST be RSA. conditions, and some simply a refusal to support a particular
feature. In general error alerts should be used for the former,
and a field in the server extension response for the latter.
All certificate profiles and key and cryptographic formats are - Extensions should as far as possible be designed to prevent any
defined by the IETF PKIX working group [PKIX]. When a key usage attack that forces use (or non-use) of a particular feature by
extension is present, the digitalSignature bit MUST be set for the manipulation of handshake messages. This principle should be
key to be eligible for signing, as described above, and the followed regardless of whether the feature is believed to cause a
keyEncipherment bit MUST be present to allow encryption, as described security problem.
above. The keyAgreement bit must be set on Diffie-Hellman
certificates.
As CipherSuites that specify new key exchange methods are specified Often the fact that the extension fields are included in the
for the TLS Protocol, they will imply certificate format and the inputs to the Finished message hashes will be sufficient, but
required encoded keying information. extreme care is needed when the extension changes the meaning of
messages sent in the handshake phase. Designers and implementors
should be aware of the fact that until the handshake has been
authenticated, active attackers can modify messages and insert,
remove, or replace extensions.
- It would be technically possible to use extensions to change major
aspects of the design of TLS; for example the design of cipher
suite negotiation. This is not recommended; it would be more
appropriate to define a new version of TLS - particularly since
the TLS handshake algorithms have specific protection against
version rollback attacks based on the version number, and the
possibility of version rollback should be a significant
consideration in any major design change.
7.4.1.4.1 Signature Algorithms
The client uses the "signature_algorithms" extension to indicate to
the server which signature/hash algorithm pairs may be used in
digital signatures. The "extension_data" field of this extension
contains a "supported_signature_algorithms" value.
enum {
none(0), md5(1), sha1(2), sha256(3), sha384(4),
sha512(5), (255)
} HashAlgorithm;
enum { anonymous(0), rsa(1), dsa(2), ecdsa(3), (255) }
SignatureAlgorithm;
struct {
HashAlgorithm hash;
SignatureAlgorithm signature;
} SignatureAndHashAlgorithm;
SignatureAndHashAlgorithm
supported_signature_algorithms<2..2^16-2>;
Each SignatureAndHashAlgorithm value lists a single hash/signature
pair which the client is willing to verify. The values are indicated
in descending order of preference.
Note: Because not all signature algorithms and hash algorithms may be
accepted by an implementation (e.g., DSA with SHA-1, but not
SHA-256), algorithms here are listed in pairs.
hash
This field indicates the hash algorithm which may be used. The
values indicate support for unhashed data, MD5 [MD5], SHA-1,
SHA-256, SHA-384, and SHA-512 [SHA] respectively. The "none" value
is provided for future extensibility, in case of a signature
algorithm which does not require hashing before signing.
signature
This field indicates the signature algorithm which may be used.
The values indicate anonymous signatures, RSASSA-PKCS1-v1_5
[PKCS1] and DSA [DSS] respectively. The "anonymous" value is
meaningless in this context but used in Section 7.4.3. It MUST NOT
appear in this extension.
The semantics of this extension are somewhat complicated because the
cipher suite indicates permissible signature algorithms but not hash
algorithm. Sections 7.4.2 and 7.4.3 describe the appropriate rules.
If the client supports only the default hash and signature algorithms
(listed in this section), it MAY omit the signature_algorithms
extension. If the client does not support the default algorithms, or
supports other hash and signature algorithms (and it is willing to
use them for verifying messages sent by server; server certificates
and server key exchange), it MUST send the signature_algorithms
extension listing the algorithms it is willing to accept.
If the client does not send the signature_algorithms extension, the
server MUST assume the following:
- If the negotiated key exchange algorithm is one of (RSA, DHE_RSA,
DH_RSA, RSA_PSK, ECDH_RSA, ECDHE_RSA), behave as if client had sent
the value (sha1,rsa).
- If the negotiated key exchange algorithm is one of (DHE_DSS,
DH_DSS), behave as if the client had sent the value (sha1,dsa).
- If the negotiated key exchange algorithm is one of (ECDH_ECDSA,
ECDHE_ECDSA), behave as if the client had sent value (sha1,ecdsa).
Note: this is a change from TLS 1.1 where there are no explicit rules
but as a practical matter one can assume that the peer supports MD5
and SHA-1.
Note: this extension is not meaningful for TLS versions prior to 1.2.
Clients MUST NOT offer it if they are offering prior versions.
However, even if clients do offer it, the rules specified in [TLSEXT]
require servers to ignore extensions they do not understand.
Servers MUST NOT send this extension. TLS servers MUST support
receiving this extension.
7.4.2. Server Certificate
When this message will be sent:
The server MUST send a certificate whenever the agreed-upon key
exchange method uses certificates for authentication (this
includes all key exchange methods defined in this document except
DH_anon). This message will always immediately follow the server
hello message.
Meaning of this message:
This message conveys the server's certificate chain to the client.
The certificate MUST be appropriate for the negotiated cipher
suite's key exchange algorithm, and any negotiated extensions.
Structure of this message: Structure of this message:
opaque ASN.1Cert<1..2^24-1>; opaque ASN.1Cert<1..2^24-1>;
struct { struct {
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
certificate_list certificate_list
This is a sequence (chain) of X.509v3 certificates. The sender's This is a sequence (chain) of certificates. The sender's
certificate must come first in the list. Each following certificate MUST come first in the list. Each following
certificate must directly certify the one preceding it. Because certificate MUST directly certify the one preceding it. Because
certificate validation requires that root keys be distributed certificate validation requires that root keys be distributed
independently, the self-signed certificate that specifies the root independently, the self-signed certificate that specifies the root
certificate authority may optionally be omitted from the chain, certificate authority MAY optionally be omitted from the chain,
under the assumption that the remote end must already possess it under the assumption that the remote end must already possess it
in order to validate it in any case. in order to validate it in any case.
The same message type and structure will be used for the client's The same message type and structure will be used for the client's
response to a certificate request message. Note that a client MAY response to a certificate request message. Note that a client MAY
send no certificates if it does not have an appropriate certificate send no certificates if it does not have an appropriate certificate
to send in response to the server's authentication request. to send in response to the server's authentication request.
Note: PKCS #7 [PKCS7] is not used as the format for the Note: PKCS #7 [PKCS7] is not used as the format for the certificate
certificate vector because PKCS #6 [PKCS6] extended vector because PKCS #6 [PKCS6] extended certificates are not used.
certificates are not used. Also, PKCS #7 defines a SET rather Also, PKCS #7 defines a SET rather than a SEQUENCE, making the task
than a SEQUENCE, making the task of parsing the list more of parsing the list more difficult.
difficult.
The following rules apply to the certificates sent by the server:
- The certificate type MUST be X.509v3, unless explicitly negotiated
otherwise (e.g., [TLSPGP]).
- The end entity certificate's public key (and associated
restrictions) MUST be compatible with the selected key exchange
algorithm.
Key Exchange Alg. Certificate Key Type
RSA RSA public key; the certificate MUST
RSA_PSK allow the key to be used for encryption
(the keyEncipherment bit MUST be set
if the key usage extension is present).
Note: RSA_PSK is defined in [TLSPSK].
DHE_RSA RSA public key; the certificate MUST
ECDHE_RSA allow the key to be used for signing
(the digitalSignature bit MUST be set
if the key usage extension is present)
with the signature scheme and hash
algorithm that will be employed in the
server key exchange message.
DHE_DSS DSA public key; the certificate MUST
allow the key to be used for signing with
the hash algorithm that will be employed
in the server key exchange message.
DH_DSS Diffie-Hellman public key; the
DH_RSA keyAgreement bit MUST be set if the
key usage extension is present.
ECDH_ECDSA ECDH-capable public key; the public key
ECDH_RSA MUST use a curve and point format supported
by the client, as described in [TLSECC].
ECDHE_ECDSA ECDSA-capable public key; the certificate
MUST allow the key to be used for signing
with the hash algorithm that will be
employed in the server key exchange
message. The public key MUST use a curve
and point format supported by the client,
as described in [TLSECC].
- The "server_name" and "trusted_ca_keys" extensions [TLSEXT] are
used to guide certificate selection.
If the client provided a "signature_algorithms" extension, then all
certificates provided by the server MUST be signed by a
hash/signature algorithm pair that appears in that extension. Note
that this implies that a certificate containing a key for one
signature algorithm MAY be signed using a different signature
algorithm (for instance, an RSA key signed with a DSA key.) This is a
departure from TLS 1.1, which required that the algorithms be the
same. Note that this also implies that the DH_DSS, DH_RSA,
ECDH_ECDSA, and ECDH_RSA key exchange algorithms do not restrict the
algorithm used to sign the certificate. Fixed DH certificates MAY be
signed with any hash/signature algorithm pair appearing in the
extension. The naming is historical.
If the server has multiple certificates, it chooses one of them based
on the above-mentioned criteria (in addition to other criteria, such
as transport layer endpoint, local configuration and preferences,
etc.). If the server has a single certificate it SHOULD attempt to
validate that it meets these criteria.
Note that there are certificates that use algorithms and/or algorithm
combinations that cannot be currently used with TLS. For example, a
certificate with RSASSA-PSS signature key (id-RSASSA-PSS OID in
SubjectPublicKeyInfo) cannot be used because TLS defines no
corresponding signature algorithm.
As cipher suites that specify new key exchange methods are specified
for the TLS Protocol, they will imply certificate format and the
required encoded keying information.
7.4.3. Server Key Exchange Message 7.4.3. Server Key Exchange Message
When this message will be sent: When this message will be sent:
This message will be sent immediately after the server certificate This message will be sent immediately after the server certificate
message (or the server hello message, if this is an anonymous message (or the server hello message, if this is an anonymous
negotiation). negotiation).
The server key exchange message is sent by the server only when The server key exchange message is sent by the server only when
the server certificate message (if sent) does not contain enough the server certificate message (if sent) does not contain enough
data to allow the client to exchange a premaster secret. This is data to allow the client to exchange a premaster secret. This is
true for the following key exchange methods: true for the following key exchange methods:
DHE_DSS DHE_DSS
DHE_RSA DHE_RSA
DH_anon DH_anon
It is not legal to send the server key exchange message for the It is not legal to send the server key exchange message for the
following key exchange methods: following key exchange methods:
RSA RSA
DH_DSS DH_DSS
DH_RSA DH_RSA
Meaning of this message: Meaning of this message:
This message conveys cryptographic information to allow the client This message conveys cryptographic information to allow the client
to communicate the premaster secret: either an RSA public key with to communicate the premaster secret: a Diffie-Hellman public key
which to encrypt the premaster secret, or a Diffie-Hellman public with which the client can complete a key exchange (with the result
key with which the client can complete a key exchange (with the being the premaster secret) or a public key for some other
result being the premaster secret). algorithm.
As additional CipherSuites are defined for TLS that include new key
exchange algorithms, the server key exchange message will be sent if
and only if the certificate type associated with the key exchange
algorithm does not provide enough information for the client to
exchange a premaster secret.
Structure of this message: Structure of this message:
enum { rsa, diffie_hellman } KeyExchangeAlgorithm; enum { dhe_dss, dhe_rsa, dh_anon, rsa, dh_dss, dh_rsa }
KeyExchangeAlgorithm;
struct {
opaque rsa_modulus<1..2^16-1>;
opaque rsa_exponent<1..2^16-1>;
} ServerRSAParams;
rsa_modulus
The modulus of the server's temporary RSA key.
rsa_exponent
The public exponent of the server's temporary RSA key.
struct { struct {
opaque dh_p<1..2^16-1>; opaque dh_p<1..2^16-1>;
opaque dh_g<1..2^16-1>; opaque dh_g<1..2^16-1>;
opaque dh_Ys<1..2^16-1>; opaque dh_Ys<1..2^16-1>;
} ServerDHParams; /* Ephemeral DH parameters */ } ServerDHParams; /* Ephemeral DH parameters */
dh_p dh_p
The prime modulus used for the Diffie-Hellman operation. The prime modulus used for the Diffie-Hellman operation.
dh_g dh_g
The generator used for the Diffie-Hellman operation. The generator used for the Diffie-Hellman operation.
dh_Ys dh_Ys
The server's Diffie-Hellman public value (g^X mod p). The server's Diffie-Hellman public value (g^X mod p).
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case diffie_hellman: case dh_anon:
ServerDHParams params; ServerDHParams params;
Signature signed_params; case dhe_dss:
case rsa: case dhe_rsa:
ServerRSAParams params;
Signature signed_params;
};
} ServerKeyExchange;
struct {
select (KeyExchangeAlgorithm) {
case diffie_hellman:
ServerDHParams params; ServerDHParams params;
digitally-signed struct {
opaque client_random[32];
opaque server_random[32];
ServerDHParams params;
} signed_params;
case rsa: case rsa:
ServerRSAParams params; case dh_dss:
case dh_rsa:
struct {} ;
/* message is omitted for rsa, dh_dss, and dh_rsa */
}; };
} ServerParams; } ServerKeyExchange;
params params
The server's key exchange parameters. The server's key exchange parameters.
signed_params signed_params
For non-anonymous key exchanges, a hash of the corresponding For non-anonymous key exchanges, a signature over the
params value, with the signature appropriate to that hash server's key exchange parameters.
applied.
md5_hash If the client has offered the "signature_algorithms" extension, the
MD5(ClientHello.random + ServerHello.random + ServerParams); signature algorithm and hash algorithm MUST be a pair listed in that
extension. Note that there is a possibility for inconsistencies here.
For instance, the client might offer DHE_DSS key exchange but omit
any DSS pairs from its "signature_algorithms" extension. In order to
negotiate correctly, the server MUST check any candidate cipher
suites against the "signature_algorithms" extension before selecting
them. This is somewhat inelegant but is a compromise designed to
minimize changes to the original cipher suite design.
sha_hash In addition, the hash and signature algorithms MUST be compatible
SHA(ClientHello.random + ServerHello.random + ServerParams); with the key in the server's end-entity certificate. RSA keys MAY be
used with any permitted hash algorithm, subject to restrictions in
the certificate, if any.
enum { anonymous, rsa, dsa } SignatureAlgorithm; Because DSA signatures do not contain any secure indication of hash
algorithm, there is a risk of hash substitution if multiple hashes
may be used with any key. Currently, DSS [DSS] may only be used with
SHA-1. Future revisions of DSS [DSS-3] are expected to allow other
digest algorithms, as well as guidance as to which digest algorithms
should be used with each key size. In addition, future revisions of
struct { [PKIX] may specify mechanisms for certificates to indicate which
select (SignatureAlgorithm) { digest algorithms are to be used with DSA.
case anonymous: struct { };
case rsa:
digitally-signed struct {
opaque md5_hash[16];
opaque sha_hash[20];
};
case dsa:
digitally-signed struct {
opaque sha_hash[20];
};
};
};
} Signature;
7.4.4. Certificate request As additional cipher suites are defined for TLS that include new key
exchange algorithms, the server key exchange message will be sent if
and only if the certificate type associated with the key exchange
algorithm does not provide enough information for the client to
exchange a premaster secret.
When this message will be sent: 7.4.4. Certificate Request
A non-anonymous server can optionally request a certificate from When this message will be sent:
the client, if it is appropriate for the selected cipher suite.
This message, if sent, will immediately follow the Server Key A non-anonymous server can optionally request a certificate from
Exchange message (if it is sent; otherwise, the Server Certificate the client, if appropriate for the selected cipher suite. This
message). message, if sent, will immediately follow the Server Key Exchange
message (if it is sent; otherwise, the Server Certificate
message).
Structure of this message: Structure of this message:
enum { enum {
rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),
rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6), rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6),
fortezza_dms_RESERVED(20), fortezza_dms_RESERVED(20), (255)
(255)
} ClientCertificateType; } ClientCertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest; } CertificateRequest;
certificate_types certificate_types
This field is a list of the types of certificates requested, A list of the types of certificate types which the client may
sorted in order of the server's preference. offer.
certificate_authorities rsa_sign a certificate containing an RSA key
A list of the distinguished names of acceptable certificate dss_sign a certificate containing a DSS key
authorities. These distinguished names may specify a desired rsa_fixed_dh a certificate containing a static DH key.
distinguished name for a root CA or for a subordinate CA; thus, dss_fixed_dh a certificate containing a static DH key
this message can be used to describe both known roots and a
desired authorization space. If the certificate_authorities
list is empty then the client MAY send any certificate of the
appropriate ClientCertificateType, unless there is some
external arrangement to the contrary.
ClientCertificateType values are divided into three groups: supported_signature_algorithms
A list of the hash/signature algorithm pairs that the server is
able to verify, listed in descending order of preference.
1. Values from 0 (zero) through 63 decimal (0x3F) inclusive are certificate_authorities
reserved for IETF Standards Track protocols. A list of the distinguished names [X501] of acceptable
certificate_authorities, represented in DER-encoded format. These
distinguished names may specify a desired distinguished name for a
root CA or for a subordinate CA; thus, this message can be used
both to describe known roots and a desired authorization space. If
the certificate_authorities list is empty then the client MAY send
any certificate of the appropriate ClientCertificateType, unless
there is some external arrangement to the contrary.
2. Values from 64 decimal (0x40) through 223 decimal (0xDF) The interaction of the certificate_types and
inclusive are reserved for assignment for non-Standards Track supported_signature_algorithms fields is somewhat complicated.
methods. certificate_types has been present in TLS since SSLv3, but was
somewhat underspecified. Much of its functionality is superseded by
supported_signature_algorithms. The following rules apply:
3. Values from 224 decimal (0xE0) through 255 decimal (0xFF) - Any certificates provided by the client MUST be signed using a
inclusive are reserved for private use. hash/signature algorithm pair found in
supported_signature_algorithms.
Additional information describing the role of IANA in the allocation - The end-entity certificate provided by the client MUST contain a
of ClientCertificateType code points is described in Section 11. key which is compatible with certificate_types. If the key is a
signature key, it MUST be usable with some hash/signature
algorithm pair in supported_signature_algorithms.
Note: Values listed as RESERVED may not be used. They were used in - For historical reasons, the names of some client certificate types
SSLv3. include the algorithm used to sign the certificate. For example,
in earlier versions of TLS, rsa_fixed_dh meant a certificate
signed with RSA and containing a static DH key. In TLS 1.2, this
functionality has been obsoleted by the
supported_signature_algorithms, and the certificate type no longer
restricts the algorithm used to sign the certificate. For
example, if the server sends dss_fixed_dh certificate type and
{{sha1, dsa}, {sha1, rsa}} signature types, the client MAY reply
with a certificate containing a static DH key, signed with RSA-
SHA1.
Note: DistinguishedName is derived from [X501]. DistinguishedNames New ClientCertificateType values are assigned by IANA as described in
are represented in DER-encoded format. Section 12.
Note: It is a fatal handshake_failure alert for an anonymous server Note: Values listed as RESERVED may not be used. They were used in
to request client authentication. SSLv3.
7.4.5. Server Hello Done Note: It is a fatal handshake_failure alert for an anonymous server
to request client authentication.
7.4.5 Server hello done
When this message will be sent: When this message will be sent:
The server hello done message is sent by the server to indicate The server hello done message is sent by the server to indicate
the end of the server hello and associated messages. After the end of the server hello and associated messages. After sending
sending this message, the server will wait for a client response. this message, the server will wait for a client response.
Meaning of this message: Meaning of this message:
This message means that the server is done sending messages to This message means that the server is done sending messages to
support the key exchange, and the client can proceed with its support the key exchange, and the client can proceed with its
phase of the key exchange. phase of the key exchange.
Upon receipt of the server hello done message, the client SHOULD Upon receipt of the server hello done message, the client SHOULD
verify that the server provided a valid certificate, if required verify that the server provided a valid certificate, if required
and check that the server hello parameters are acceptable. and check that the server hello parameters are acceptable.
Structure of this message: Structure of this message:
struct { } ServerHelloDone; struct { } ServerHelloDone;
7.4.6. Client certificate 7.4.6. Client Certificate
When this message will be sent: When this message will be sent:
This is the first message the client can send after receiving a This is the first message the client can send after receiving a
server hello done message. This message is only sent if the server hello done message. This message is only sent if the server
server requests a certificate. If no suitable certificate is requests a certificate. If no suitable certificate is available,
available, the client SHOULD send a certificate message containing the client MUST send a certificate message containing no
no certificates. That is, the certificate_list structure has a certificates. That is, the certificate_list structure has a length
length of zero. If client authentication is required by the of zero. If the client does not send any certificates, the server
server for the handshake to continue, it may respond with a fatal MAY at its discretion either continue the handshake without client
handshake failure alert. Client certificates are sent using the authentication, or respond with a fatal handshake_failure alert.
Certificate structure defined in Section 7.4.2. Also, if some aspect of the certificate chain was unacceptable
(e.g., it was not signed by a known, trusted CA), the server MAY
at its discretion either continue the handshake (considering the
client unauthenticated) or send a fatal alert.
Note: When using a static Diffie-Hellman based key exchange method Client certificates are sent using the Certificate structure
(DH_DSS or DH_RSA), if client authentication is requested, the defined in Section 7.4.2.
Diffie-Hellman group and generator encoded in the client's
certificate MUST match the server specified Diffie-Hellman Meaning of this message:
parameters if the client's parameters are to be used for the key
exchange. This message conveys the client's certificate chain to the server;
the server will use it when verifying the certificate verify
message (when the client authentication is based on signing), or
calculate the premaster secret (for non-ephemeral Diffie-Hellman).
The certificate MUST be appropriate for the negotiated cipher
suite's key exchange algorithm, and any negotiated extensions.
In particular:
- The certificate type MUST be X.509v3, unless explicitly negotiated
otherwise (e.g. [TLSPGP]).
- The end-entity certificate's public key (and associated
restrictions) has to be compatible with the certificate types
listed in CertificateRequest:
Client Cert. Type Certificate Key Type
rsa_sign RSA public key; the certificate MUST allow
the key to be used for signing with the
signature scheme and hash algorithm that
will be employed in the certificate verify
message.
dss_sign DSA public key; the certificate MUST allow
the key to be used for signing with the
hash algorithm that will be employed in
the certificate verify message.
ecdsa_sign ECDSA-capable public key; the certificate
MUST allow the key to be used for signing
with the hash algorithm that will be
employed in the certificate verify
message; the public key MUST use a
curve and point format supported by the
server.
rsa_fixed_dh Diffie-Hellman public key; MUST use
dss_fixed_dh the same parameters as server's key.
rsa_fixed_ecdh ECDH-capable public key; MUST use
ecdsa_fixed_ecdh the same curve as server's key, and
MUST use a point format supported by
the server.
- If the certificate_authorities list in the certificate request
message was non-empty, one of the certificates in the certificate
chain SHOULD be issued by one of the listed CAs.
- The certificates MUST be signed using an acceptable hash/
signature algorithm pair, as described in Section 7.4.4. Note that
this relaxes the constraints on certificate signing algorithms
found in prior versions of TLS.
Note that as with the server certificate, there are certificates that
use algorithms/algorithm combinations that cannot be currently used
with TLS.
7.4.7. Client Key Exchange Message 7.4.7. Client Key Exchange Message
When this message will be sent: When this message will be sent:
This message is always sent by the client. It MUST immediately This message is always sent by the client. It MUST immediately
follow the client certificate message, if it is sent. Otherwise follow the client certificate message, if it is sent. Otherwise it
it MUST be the first message sent by the client after it receives MUST be the first message sent by the client after it receives the
the server hello done message. server hello done message.
Meaning of this message: Meaning of this message:
With this message, the premaster secret is set, either though With this message, the premaster secret is set, either though
direct transmission of the RSA-encrypted secret or by the direct transmission of the RSA-encrypted secret, or by the
transmission of Diffie-Hellman parameters that will allow each transmission of Diffie-Hellman parameters that will allow each
side to agree upon the same premaster secret. When the key side to agree upon the same premaster secret.
exchange method is DH_RSA or DH_DSS, client certification has been
requested, and the client was able to respond with a certificate When the client is using an ephemeral Diffie-Hellman exponent,
that contained a Diffie-Hellman public key whose parameters (group then this message contains the client's Diffie-Hellman public
and generator) matched those specified by the server in its value. If the client is sending a certificate containing a static
certificate, this message MUST not contain any data. DH exponent (i.e., it is doing fixed_dh client authentication)
then this message MUST be sent but MUST be empty.
Structure of this message: Structure of this message:
The choice of messages depends on which key exchange method has The choice of messages depends on which key exchange method has
been selected. See Section 7.4.3 for the KeyExchangeAlgorithm been selected. See Section 7.4.3 for the KeyExchangeAlgorithm
definition. definition.
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret; case rsa:
case diffie_hellman: ClientDiffieHellmanPublic; EncryptedPreMasterSecret;
case dhe_dss:
case dhe_rsa:
case dh_dss:
case dh_rsa:
case dh_anon:
ClientDiffieHellmanPublic;
} exchange_keys; } exchange_keys;
} ClientKeyExchange; } ClientKeyExchange;
7.4.7.1. RSA Encrypted Premaster Secret Message 7.4.7.1. RSA Encrypted Premaster Secret Message
Meaning of this message: Meaning of this message:
If RSA is being used for key agreement and authentication, the If RSA is being used for key agreement and authentication, the
client generates a 48-byte premaster secret, encrypts it using the client generates a 48-byte premaster secret, encrypts it using the
public key from the server's certificate or the temporary RSA key public key from the server's certificate and sends the result in
provided in a server key exchange message, and sends the result in an encrypted premaster secret message. This structure is a variant
an encrypted premaster secret message. This structure is a of the client key exchange message and is not a message in itself.
variant of the client key exchange message and is not a message in
itself.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
opaque random[46]; opaque random[46];
} PreMasterSecret; } PreMasterSecret;
client_version The latest (newest) version supported by the client_version
client. This is used to detect version roll-back attacks. The latest (newest) version supported by the client. This is
Upon receiving the premaster secret, the server SHOULD check used to detect version roll-back attacks.
that this value matches the value transmitted by the client in
the client hello message.
random random
46 securely-generated random bytes. 46 securely-generated random bytes.
struct { struct {
public-key-encrypted PreMasterSecret pre_master_secret; public-key-encrypted PreMasterSecret pre_master_secret;
} EncryptedPreMasterSecret; } EncryptedPreMasterSecret;
pre_master_secret pre_master_secret
This random value is generated by the client and is used to This random value is generated by the client and is used to
generate the master secret, as specified in Section 8.1. generate the master secret, as specified in Section 8.1.
Note: An attack discovered by Daniel Bleichenbacher [BLEI] can be Note: The version number in the PreMasterSecret is the version
used to attack a TLS server that is using PKCS#1 v 1.5 encoded offered by the client in the ClientHello.client_version, not the
RSA. The attack takes advantage of the fact that, by failing version negotiated for the connection. This feature is designed to
in different ways, a TLS server can be coerced into revealing prevent rollback attacks. Unfortunately, some old implementations
whether a particular message, when decrypted, is properly use the negotiated version instead and therefore checking the version
PKCS#1 v1.5 formatted or not. number may lead to failure to interoperate with such incorrect client
implementations.
The best way to avoid vulnerability to this attack is to treat Client implementations MUST always send the correct version number in
incorrectly formatted messages in a manner indistinguishable PreMasterSecret. If ClientHello.client_version is TLS 1.1 or higher,
from correctly formatted RSA blocks. Thus, when a server server implementations MUST check the version number as described in
receives an incorrectly formatted RSA block, it should generate the note below. If the version number is 1.0 or earlier, server
a random 48-byte value and proceed using it as the premaster implementations SHOULD check the version number, but MAY have a
secret. Thus, the server will act identically whether the configuration option to disable the check. Note that if the check
received RSA block is correctly encoded or not. fails, the PreMasterSecret SHOULD be randomized as described below.
[PKCS1B] defines a newer version of PKCS#1 encoding that is Note: Attacks discovered by Bleichenbacher [BLEI] and Klima et al.
more secure against the Bleichenbacher attack. However, for [KPR03] can be used to attack a TLS server that reveals whether a
maximal compatibility with TLS 1.0, TLS 1.1 retains the particular message, when decrypted, is properly PKCS#1 formatted,
original encoding. No variants of the Bleichenbacher attack contains a valid PreMasterSecret structure, or has the correct
are known to exist provided that the above recommendations are version number.
followed.
The best way to avoid these vulnerabilities is to treat incorrectly
formatted messages in a manner indistinguishable from correctly
formatted RSA blocks. In other words:
1. Generate a string R of 46 random bytes
2. Decrypt the message M
3. If the PKCS#1 padding is not correct, or the length of
message M is not exactly 48 bytes:
premaster secret = ClientHello.client_version || R
else If ClientHello.client_version <= TLS 1.0, and
version number check is explicitly disabled:
premaster secret = M
else:
premaster secret = ClientHello.client_version || M[2..47]
Note that explicitly constructing the premaster_secret with the
ClientHello.client_version produces an invalid master_secret if the
client has sent the wrong version in the original premaster_secret.
In any case, a TLS server MUST NOT generate an alert if processing an
RSA-encrypted premaster secret message fails, or the version number
is not as expected. Instead, it MUST continue the handshake with a
randomly generated premaster secret. It may be useful to log the
real cause of failure for troubleshooting purposes; however, care
must be taken to avoid leaking the information to an attacker
(through, e.g., timing, log files, or other channels.)
The RSAES-OAEP encryption scheme defined in [PKCS1] is more secure
against the Bleichenbacher attack. However, for maximal compatibility
with earlier versions of TLS, this specification uses the RSAES-
PKCS1-v1_5 scheme. No variants of the Bleichenbacher attack are known
to exist provided that the above recommendations are followed.
Implementation Note: Public-key-encrypted data is represented as an Implementation Note: Public-key-encrypted data is represented as an
opaque vector <0..2^16-1> (see Section 4.7). opaque vector <0..2^16-1> (see Section 4.7). Thus, the RSA-encrypted
Thus, the RSA-encrypted PreMasterSecret in a PreMasterSecret in a ClientKeyExchange is preceded by two length
ClientKeyExchange is preceded by two length bytes. These bytes are redundant in the case of RSA because the
bytes. These bytes are redundant in the case of EncryptedPreMasterSecret is the only data in the ClientKeyExchange
RSA because the EncryptedPreMasterSecret is the and its length can therefore be unambiguously determined. The SSLv3
only data in the ClientKeyExchange and its specification was not clear about the encoding of public-key-
length can therefore be unambiguously encrypted data, and therefore many SSLv3 implementations do not
determined. The SSLv3 specification was not include the the length bytes, encoding the RSA encrypted data
clear about the encoding of public-key-encrypted directly in the ClientKeyExchange message.
data, and therefore many SSLv3 implementations
do not include the length bytes, encoding the
RSA encrypted data directly in the
ClientKeyExchange message.
This specification requires correct encoding of This specification requires correct encoding of the
the EncryptedPreMasterSecret complete with EncryptedPreMasterSecret complete with length bytes. The resulting
length bytes. The resulting PDU is incompatible PDU is incompatible with many SSLv3 implementations. Implementors
with many SSLv3 implementations. Implementors upgrading from SSLv3 MUST modify their implementations to generate
upgrading from SSLv3 must modify their and accept the correct encoding. Implementors who wish to be
implementations to generate and accept the compatible with both SSLv3 and TLS should make their implementation's
correct encoding. Implementors who wish to be behavior dependent on the protocol version.
compatible with both SSLv3 and TLS should make
their implementation's behavior dependent on the
protocol version.
Implementation Note: It is now known that remote timing-based attacks Implementation Note: It is now known that remote timing-based attacks
on SSL are possible, at least when the client on TLS are possible, at least when the client and server are on the
and server are on the same LAN. Accordingly, same LAN. Accordingly, implementations that use static RSA keys MUST
implementations that use static RSA keys SHOULD use RSA blinding or some other anti-timing technique, as described in
use RSA blinding or some other anti-timing [TIMING].
technique, as described in [TIMING].
Note: The version number in the PreMasterSecret MUST be the version
offered by the client in the ClientHello, not the version
negotiated for the connection. This feature is designed to
prevent rollback attacks. Unfortunately, many implementations
use the negotiated version instead, and therefore checking the
version number may lead to failure to interoperate with such
incorrect client implementations. Client implementations, MUST
and Server implementations MAY, check the version number. In
practice, since the TLS handshake MACs prevent downgrade and no
good attacks are known on those MACs, ambiguity is not
considered a serious security risk. Note that if servers
choose to check the version number, they should randomize the
PreMasterSecret in case of error, rather than generate an
alert, in order to avoid variants on the Bleichenbacher attack.
[KPR03]
7.4.7.2. Client Diffie-Hellman Public Value 7.4.7.2. Client Diffie-Hellman Public Value
Meaning of this message: Meaning of this message:
This structure conveys the client's Diffie-Hellman public value This structure conveys the client's Diffie-Hellman public value
(Yc) if it was not already included in the client's certificate. (Yc) if it was not already included in the client's certificate.
The encoding used for Yc is determined by the enumerated The encoding used for Yc is determined by the enumerated
PublicValueEncoding. This structure is a variant of the client PublicValueEncoding. This structure is a variant of the client key
key exchange message and not a message in itself. exchange message, and not a message in itself.
Structure of this message: Structure of this message:
enum { implicit, explicit } PublicValueEncoding; enum { implicit, explicit } PublicValueEncoding;
implicit implicit
If the client certificate already contains a suitable Diffie- If the client has sent a certificate which contains a suitable
Hellman key, then Yc is implicit and does not need to be sent Diffie-Hellman key (for fixed_dh client authentication) then Yc
again. In this case, the client key exchange message will be is implicit and does not need to be sent again. In this case,
sent, but it MUST be empty. the client key exchange message will be sent, but it MUST be
empty.
explicit explicit
Yc needs to be sent. Yc needs to be sent.
struct { struct {
select (PublicValueEncoding) { select (PublicValueEncoding) {
case implicit: struct { }; case implicit: struct { };
case explicit: opaque dh_Yc<1..2^16-1>; case explicit: opaque dh_Yc<1..2^16-1>;
} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
dh_Yc dh_Yc
The client's Diffie-Hellman public value (Yc). The client's Diffie-Hellman public value (Yc).
7.4.8. Certificate verify 7.4.8. Certificate verify
When this message will be sent: When this message will be sent:
This message is used to provide explicit verification of a client This message is used to provide explicit verification of a client
certificate. This message is only sent following a client certificate. This message is only sent following a client
certificate that has signing capability (i.e., all certificates certificate that has signing capability (i.e. all certificates
except those containing fixed Diffie-Hellman parameters). When except those containing fixed Diffie-Hellman parameters). When
sent, it MUST immediately follow the client key exchange message. sent, it MUST immediately follow the client key exchange message.
Structure of this message: Structure of this message:
struct { struct {
Signature signature; digitally-signed struct {
opaque handshake_messages[handshake_messages_length];
}
} CertificateVerify; } CertificateVerify;
The Signature type is defined in 7.4.3. Here handshake_messages refers to all handshake messages sent or
received starting at client hello up to but not including this
CertificateVerify.signature.md5_hash message, including the type and length fields of the handshake
MD5(handshake_messages); messages. This is the concatenation of all the Handshake
structures as defined in 7.4 exchanged thus far. Note that this
requires both sides to either buffer the messages or compute
running hashes for all potential hash algorithms up to the time of
the CertificateVerify computation. Servers can minimize this
computation cost by offering a restricted set of digest algorithms
in the CertificateRequest message.
CertificateVerify.signature.sha_hash The hash and signature algorithms used in the signature MUST be
SHA(handshake_messages); one of those present in the supported_signature_algorithms field
of the CertificateRequest message. In addition, the hash and
signature algorithms MUST be compatible with the key in the
client's end-entity certificate. RSA keys MAY be used with any
permitted hash algorith, subject to restrictions in the
certificate, if any.
Here handshake_messages refers to all handshake messages sent or Because DSA signatures do not contain any secure indication of
received starting at client hello up to but not including this hash algorithm, there is a risk of hash substitution if multiple
message, including the type and length fields of the handshake hashes may be used with any key. Currently, DSS [DSS] may only be
messages. This is the concatenation of all the Handshake structures, used with SHA-1. Future revisions of DSS [DSS-3] are expected to
as defined in 7.4, exchanged thus far. allow other digest algorithms, as well as guidance as to which
digest algorithms should be used with each key size. In addition,
future revisions of [PKIX] may specify mechanisms for certificates
to indicate which digest algorithms are to be used with DSA.
7.4.9. Finished 7.4.9. Finished
When this message will be sent: When this message will be sent:
A finished message is always sent immediately after a change A finished message is always sent immediately after a change
cipher spec message to verify that the key exchange and cipher spec message to verify that the key exchange and
authentication processes were successful. It is essential that a authentication processes were successful. It is essential that a
change cipher spec message be received between the other handshake change cipher spec message be received between the other handshake
messages and the Finished message. messages and the Finished message.
Meaning of this message: Meaning of this message:
The finished message is the first protected with the just- The finished message is the first protected with the just-
negotiated algorithms, keys, and secrets. Recipients of finished negotiated algorithms, keys, and secrets. Recipients of finished
messages MUST verify that the contents are correct. Once a side messages MUST verify that the contents are correct. Once a side
has sent its Finished message and received and validated the has sent its Finished message and received and validated the
Finished message from its peer, it may begin to send and receive Finished message from its peer, it may begin to send and receive
application data over the connection. application data over the connection.
Structure of this message:
struct { struct {
opaque verify_data[12]; opaque verify_data[verify_data_length];
} Finished; } Finished;
verify_data verify_data
PRF(master_secret, finished_label, MD5(handshake_messages) + PRF(master_secret, finished_label, Hash(handshake_messages))
SHA-1(handshake_messages)) [0..11]; [0..verify_data_length-1];
finished_label finished_label
For Finished messages sent by the client, the string "client For Finished messages sent by the client, the string "client
finished". For Finished messages sent by the server, the finished". For Finished messages sent by the server, the string
string "server finished". "server finished".
Hash denotes a Hash of the handshake messages. For the PRF defined
in Section 5, the Hash MUST be the Hash used as the basis for the
PRF. Any cipher suite which defines a different PRF MUST also
define the Hash to use in the Finished computation.
In previous versions of TLS, the verify_data was always 12 octets
long. In the current version of TLS, it depends on the cipher
suite. Any cipher suite which does not explicitly specify
verify_data_length has a verify_data_length equal to 12. This
includes all existing cipher suites. Note that this
representation has the same encoding as with previous versions.
Future cipher suites MAY specify other lengths but such length
MUST be at least 12 bytes.
handshake_messages handshake_messages
All of the data from all messages in this handshake (not All of the data from all messages in this handshake (not
including any HelloRequest messages) up to but not including including any HelloRequest messages) up to but not including
this message. This is only data visible at the handshake this message. This is only data visible at the handshake layer
layer and does not include record layer headers. This is the and does not include record layer headers. This is the
concatenation of all the Handshake structures, as defined in concatenation of all the Handshake structures as defined in
7.4, exchanged thus far. 7.4, exchanged thus far.
It is a fatal error if a finished message is not preceded by a change It is a fatal error if a finished message is not preceded by a change
cipher spec message at the appropriate point in the handshake. cipher spec message at the appropriate point in the handshake.
The value handshake_messages includes all handshake messages starting The value handshake_messages includes all handshake messages starting
at client hello up to, but not including, this finished message. at client hello up to, but not including, this finished message. This
This may be different from handshake_messages in Section 7.4.8 may be different from handshake_messages in Section 7.4.8 because it
because it would include the certificate verify message (if sent). would include the certificate verify message (if sent). Also, the
Also, the handshake_messages for the finished message sent by the handshake_messages for the finished message sent by the client will
client will be different from that for the finished message sent by be different from that for the finished message sent by the server,
the server, because the one that is sent second will include the because the one that is sent second will include the prior one.
prior one.
Note: Change cipher spec messages, alerts, and any other record types Note: Change cipher spec messages, alerts, and any other record types
are not handshake messages and are not included in the hash are not handshake messages and are not included in the hash
computations. Also, Hello Request messages are omitted from computations. Also, Hello Request messages are omitted from handshake
handshake hashes. hashes.
8. Cryptographic Computations 8. Cryptographic Computations
In order to begin connection protection, the TLS Record Protocol In order to begin connection protection, the TLS Record Protocol
requires specification of a suite of algorithms, a master secret, and requires specification of a suite of algorithms, a master secret, and
the client and server random values. The authentication, encryption, the client and server random values. The authentication, encryption,
and MAC algorithms are determined by the cipher_suite selected by the and MAC algorithms are determined by the cipher_suite selected by the
server and revealed in the server hello message. The compression server and revealed in the server hello message. The compression
algorithm is negotiated in the hello messages, and the random values algorithm is negotiated in the hello messages, and the random values
are exchanged in the hello messages. All that remains is to are exchanged in the hello messages. All that remains is to calculate
calculate the master secret. the master secret.
8.1. Computing the Master Secret 8.1. Computing the Master Secret
For all key exchange methods, the same algorithm is used to convert For all key exchange methods, the same algorithm is used to convert
the pre_master_secret into the master_secret. The pre_master_secret the pre_master_secret into the master_secret. The pre_master_secret
should be deleted from memory once the master_secret has been should be deleted from memory once the master_secret has been
computed. computed.
master_secret = PRF(pre_master_secret, "master secret", master_secret = PRF(pre_master_secret, "master secret",
ClientHello.random + ServerHello.random) ClientHello.random + ServerHello.random)
[0..47]; [0..47];
The master secret is always exactly 48 bytes in length. The length The master secret is always exactly 48 bytes in length. The length of
of the premaster secret will vary depending on key exchange method. the premaster secret will vary depending on key exchange method.
8.1.1. RSA 8.1.1. RSA
When RSA is used for server authentication and key exchange, a 48- When RSA is used for server authentication and key exchange, a
byte pre_master_secret is generated by the client, encrypted under 48-byte pre_master_secret is generated by the client, encrypted under
the server's public key, and sent to the server. The server uses its the server's public key, and sent to the server. The server uses its
private key to decrypt the pre_master_secret. Both parties then private key to decrypt the pre_master_secret. Both parties then
convert the pre_master_secret into the master_secret, as specified convert the pre_master_secret into the master_secret, as specified
above. above.
RSA digital signatures are performed using PKCS #1 [PKCS1] block type
1. RSA public key encryption is performed using PKCS #1 block type 2.
8.1.2. Diffie-Hellman 8.1.2. Diffie-Hellman
A conventional Diffie-Hellman computation is performed. The A conventional Diffie-Hellman computation is performed. The
negotiated key (Z) is used as the pre_master_secret, and is converted negotiated key (Z) is used as the pre_master_secret, and is converted
into the master_secret, as specified above. Leading bytes of Z that into the master_secret, as specified above. Leading bytes of Z that
contain all zero bits are stripped before it is used as the contain all zero bits are stripped before it is used as the
pre_master_secret. pre_master_secret.
Note: Diffie-Hellman parameters are specified by the server and may Note: Diffie-Hellman parameters are specified by the server and may
be either ephemeral or contained within the server's be either ephemeral or contained within the server's certificate.
certificate.
9. Mandatory Cipher Suites 9. Mandatory Cipher Suites
In the absence of an application profile standard specifying In the absence of an application profile standard specifying
otherwise, a TLS compliant application MUST implement the cipher otherwise, a TLS compliant application MUST implement the cipher
suite TLS_RSA_WITH_3DES_EDE_CBC_SHA. suite TLS_RSA_WITH_AES_128_CBC_SHA.
10. Application Data Protocol 10. Application Data Protocol
Application data messages are carried by the Record Layer and are Application data messages are carried by the Record Layer and are
fragmented, compressed, and encrypted based on the current connection fragmented, compressed, and encrypted based on the current connection
state. The messages are treated as transparent data to the record state. The messages are treated as transparent data to the record
layer. layer.
11. Security Considerations 11. Security Considerations
Security issues are discussed throughout this memo, especially in Security issues are discussed throughout this memo, especially in
Appendices D, E, and F. Appendices D, E, and F.
12. IANA Considerations 12. IANA Considerations
This document describes a number of new registries that have been This document uses several registries that were originally created in
created by IANA. We recommended that they be placed as individual [TLS1.1]. IANA is requested to update (has updated) these to
registries items under a common TLS category. reference this document. The registries and their allocation policies
(unchanged from [TLS1.1]) are listed below.
Section 7.4.3 describes a TLS ClientCertificateType Registry to be - TLS ClientCertificateType Identifiers Registry: Future values in
maintained by the IANA, defining a number of such code point the range 0-63 (decimal) inclusive are assigned via Standards
identifiers. ClientCertificateType identifiers with values in the Action [RFC2434]. Values in the range 64-223 (decimal) inclusive
range 0-63 (decimal) inclusive are assigned via RFC 2434 Standards are assigned Specification Required [RFC2434]. Values from 224-255
Action. Values from the range 64-223 (decimal) inclusive are (decimal) inclusive are reserved for Private Use [RFC2434].
assigned via [RFC2434] Specification Required. Identifier values
from 224-255 (decimal) inclusive are reserved for RFC 2434 Private
Use. The registry will initially be populated with the values in
this document, Section 7.4.4.
Section A.5 describes a TLS Cipher Suite Registry to be maintained by - TLS Cipher Suite Registry: Future values with the first byte in
the IANA, and it defines a number of such cipher suite identifiers. the range 0-191 (decimal) inclusive are assigned via Standards
Cipher suite values with the first byte in the range 0-191 (decimal) Action [RFC2434]. Values with the first byte in the range 192-254
inclusive are assigned via RFC 2434 Standards Action. Values with (decimal) are assigned via Specification Required [RFC2434].
the first byte in the range 192-254 (decimal) are assigned via RFC Values with the first byte 255 (decimal) are reserved for Private
2434 Specification Required. Values with the first byte 255 Use [RFC2434].
(decimal) are reserved for RFC 2434 Private Use. The registry will
initially be populated with the values from Section A.5 of this
document, [TLSAES], and from Section 3 of [TLSKRB].
Section 6 requires that all ContentType values be defined by RFC 2434 - This document defines several new HMAC-SHA256 based cipher suites,
Standards Action. IANA has created a TLS ContentType registry, whose values (in Appendix A.5) are to be (have been) allocated
initially populated with values from Section 6.2.1 of this document. from the TLS Cipher Suite registry.
Future values MUST be allocated via Standards Action as described in
[RFC2434].
Section 7.2.2 requires that all Alert values be defined by RFC 2434 - TLS ContentType Registry: Future values are allocated via
Standards Action. IANA has created a TLS Alert registry, initially Standards Action [RFC2434].
populated with values from Section 7.2 of this document and from
Section 4 of [TLSEXT]. Future values MUST be allocated via Standards
Action as described in [RFC2434].
Section 7.4 requires that all HandshakeType values be defined by RFC - TLS Alert Registry: Future values are allocated via Standards
2434 Standards Action. IANA has created a TLS HandshakeType Action [RFC2434].
registry, initially populated with values from Section 7.4 of this
document and from Section 2.4 of [TLSEXT]. Future values MUST be - TLS HandshakeType Registry: Future values are allocated via
allocated via Standards Action as described in [RFC2434]. Standards Action [RFC2434].
This document also uses a registry originally created in [RFC4366].
IANA is requested to update (has updated) it to reference this
document. The registry and its allocation policy (unchanged from
[RFC4366]) is listed below:
- TLS ExtensionType Registry: Future values are allocated via IETF
Consensus [RFC2434]
In addition, this document defines two new registries to be
maintained by IANA:
- TLS SignatureAlgorithm Registry: The registry will be initially
populated with the values described in Section 7.4.1.4.1. Future
values in the range 0-63 (decimal) inclusive are assigned via
Standards Action [RFC2434]. Values in the range 64-223 (decimal)
inclusive are assigned via Specification Required [RFC2434].
Values from 224-255 (decimal) inclusive are reserved for Private
Use [RFC2434].
- TLS HashAlgorithm Registry: The registry will be initially
populated with the values described in Section 7.4.1.4.1. Future
values in the range 0-63 (decimal) inclusive are assigned via
Standards Action [RFC2434]. Values in the range 64-223 (decimal)
inclusive are assigned via Specification Required [RFC2434].
Values from 224-255 (decimal) inclusive are reserved for Private
Use [RFC2434].
This document defines one new TLS extension, signature_algorithms,
which is to be (has been) allocated value TBD-BY-IANA in the TLS
ExtensionType registry.
This document also uses the TLS Compression Method Identifiers
Registry, defined in [RFC3749]. IANA is requested to allocate value
0 for the "null" compression method.
Appendix A. Protocol Constant Values Appendix A. Protocol Constant Values
This section describes protocol types and constants. This section describes protocol types and constants.
A.1. Record Layer A.1. Record Layer
struct { struct {
uint8 major, minor; uint8 major;
uint8 minor;
} ProtocolVersion; } ProtocolVersion;
ProtocolVersion version = { 3, 2 }; /* TLS v1.1 */ ProtocolVersion version = { 3, 3 }; /* TLS v1.2*/
enum { enum {
change_cipher_spec(20), alert(21), handshake(22), change_cipher_spec(20), alert(21), handshake(22),
application_data(23), (255) application_data(23), (255)
} ContentType; } ContentType;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
skipping to change at page 55, line 40 skipping to change at page 64, line 41
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
opaque fragment[TLSCompressed.length]; opaque fragment[TLSCompressed.length];
} TLSCompressed; } TLSCompressed;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion version; ProtocolVersion version;
uint16 length; uint16 length;
select (CipherSpec.cipher_type) { select (SecurityParameters.cipher_type) {
case stream: GenericStreamCipher; case stream: GenericStreamCipher;
case block: GenericBlockCipher; case block: GenericBlockCipher;
case aead: GenericAEADCipher;
} fragment; } fragment;
} TLSCiphertext; } TLSCiphertext;
stream-ciphered struct { stream-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[CipherSpec.hash_size]; opaque MAC[SecurityParameters.mac_length];
} GenericStreamCipher; } GenericStreamCipher;
struct {
block-ciphered struct { opaque IV[SecurityParameters.record_iv_length];
opaque IV[CipherSpec.block_length]; block-ciphered struct {
opaque content[TLSCompressed.length]; opaque content[TLSCompressed.length];
opaque MAC[CipherSpec.hash_size]; opaque MAC[SecurityParameters.mac_length];
uint8 padding[GenericBlockCipher.padding_length]; uint8 padding[GenericBlockCipher.padding_length];
uint8 padding_length; uint8 padding_length;
};
} GenericBlockCipher; } GenericBlockCipher;
aead-ciphered struct {
opaque IV[SecurityParameters.record_iv_length];
opaque aead_output[AEADEncrypted.length];
} GenericAEADCipher;
A.2. Change Cipher Specs Message A.2. Change Cipher Specs Message
struct { struct {
enum { change_cipher_spec(1), (255) } type; enum { change_cipher_spec(1), (255) } type;
} ChangeCipherSpec; } ChangeCipherSpec;
A.3. Alert Messages A.3. Alert Messages
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
decryption_failed(21), decryption_failed_RESERVED(21),
record_overflow(22), record_overflow(22),
decompression_failure(30), decompression_failure(30),
handshake_failure(40), handshake_failure(40),
no_certificate_RESERVED (41), no_certificate_RESERVED(41),
bad_certificate(42), bad_certificate(42),
unsupported_certificate(43), unsupported_certificate(43),
certificate_revoked(44), certificate_revoked(44),
certificate_expired(45), certificate_expired(45),
certificate_unknown(46), certificate_unknown(46),
illegal_parameter(47), illegal_parameter(47),
unknown_ca(48), unknown_ca(48),
access_denied(49), access_denied(49),
decode_error(50), decode_error(50),
decrypt_error(51), decrypt_error(51),
export_restriction_RESERVED(60), export_restriction_RESERVED(60),
protocol_version(70), protocol_version(70),
insufficient_security(71), insufficient_security(71),
internal_error(80), internal_error(80),
user_canceled(90), user_canceled(90),
no_renegotiation(100), no_renegotiation(100),
(255) unsupported_extension(110), /* new */
} AlertDescription; (255)
} AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
A.4. Handshake Protocol A.4. Handshake Protocol
enum { enum {
hello_request(0), client_hello(1), server_hello(2), hello_request(0), client_hello(1), server_hello(2),
certificate(11), server_key_exchange (12), certificate(11), server_key_exchange (12),
certificate_request(13), server_hello_done(14), certificate_request(13), server_hello_done(14),
certificate_verify(15), client_key_exchange(16), certificate_verify(15), client_key_exchange(16),
finished(20), (255) finished(20)
(255)
} HandshakeType; } HandshakeType;
struct { struct {
HandshakeType msg_type; HandshakeType msg_type;
uint24 length; uint24 length;
select (HandshakeType) { select (HandshakeType) {
case hello_request: HelloRequest; case hello_request: HelloRequest;
case client_hello: ClientHello; case client_hello: ClientHello;
case server_hello: ServerHello; case server_hello: ServerHello;
case certificate: Certificate; case certificate: Certificate;
case server_key_exchange: ServerKeyExchange; case server_key_exchange: ServerKeyExchange;
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case server_hello_done: ServerHelloDone; case server_hello_done: ServerHelloDone;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case client_key_exchange: ClientKeyExchange; case client_key_exchange: ClientKeyExchange;
case finished: Finished; case finished: Finished;
} body; } body;
} Handshake; } Handshake;
A.4.1. Hello messages A.4.1. Hello Messages
struct { } HelloRequest; struct { } HelloRequest;
struct { struct {
uint32 gmt_unix_time; uint32 gmt_unix_time;
opaque random_bytes[28]; opaque random_bytes[28];
} Random; } Random;
opaque SessionID<0..32>; opaque SessionID<0..32>;
uint8 CipherSuite[2]; uint8 CipherSuite[2];
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
skipping to change at page 57, line 51 skipping to change at page 67, line 14
opaque SessionID<0..32>; opaque SessionID<0..32>;
uint8 CipherSuite[2]; uint8 CipherSuite[2];
enum { null(0), (255) } CompressionMethod; enum { null(0), (255) } CompressionMethod;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suites<2..2^16-1>; CipherSuite cipher_suites<2..2^16-2>;
CompressionMethod compression_methods<1..2^8-1>; CompressionMethod compression_methods<1..2^8-1>;
select (extensions_present) {
case false:
struct {};
case true:
Extension extensions<0..2^16-1>;
};
} ClientHello; } ClientHello;
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
Random random; Random random;
SessionID session_id; SessionID session_id;
CipherSuite cipher_suite; CipherSuite cipher_suite;
CompressionMethod compression_method; CompressionMethod compression_method;
select (extensions_present) {
case false:
struct {};
case true:
Extension extensions<0..2^16-1>;
};
} ServerHello; } ServerHello;
struct {
ExtensionType extension_type;
opaque extension_data<0..2^16-1>;
} Extension;
enum {
signature_algorithms(TBD-BY-IANA), (65535)
} ExtensionType;
enum{
none(0), md5(1), sha1(2), sha256(3), sha384(4),
sha512(5), (255)
} HashAlgorithm;
enum { anonymous(0), rsa(1), dsa(2), (255) } SignatureAlgorithm;
struct {
HashAlgorithm hash;
SignatureAlgorithm signature;
} SignatureAndHashAlgorithm;
SignatureAndHashAlgorithm
supported_signature_algorithms<2..2^16-1>;
A.4.2. Server Authentication and Key Exchange Messages A.4.2. Server Authentication and Key Exchange Messages
opaque ASN.1Cert<2^24-1>; opaque ASN.1Cert<2^24-1>;
struct { struct {
ASN.1Cert certificate_list<0..2^24-1>; ASN.1Cert certificate_list<0..2^24-1>;
} Certificate; } Certificate;
enum { rsa, diffie_hellman } KeyExchangeAlgorithm; enum { dhe_dss, dhe_rsa, dh_anon, rsa,dh_dss, dh_rsa}
KeyExchangeAlgorithm;
struct {
opaque rsa_modulus<1..2^16-1>;
opaque rsa_exponent<1..2^16-1>;
} ServerRSAParams;
struct { struct {
opaque dh_p<1..2^16-1>; opaque dh_p<1..2^16-1>;
opaque dh_g<1..2^16-1>; opaque dh_g<1..2^16-1>;
opaque dh_Ys<1..2^16-1>; opaque dh_Ys<1..2^16-1>;
} ServerDHParams; } ServerDHParams; /* Ephemeral DH parameters */
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case diffie_hellman: case dh_anon:
ServerDHParams params; ServerDHParams params;
Signature signed_params; case dhe_dss:
case rsa: case dhe_rsa:
ServerRSAParams params;
Signature signed_params;
};
} ServerKeyExchange;
enum { anonymous, rsa, dsa } SignatureAlgorithm;
struct {
select (KeyExchangeAlgorithm) {
case diffie_hellman:
ServerDHParams params; ServerDHParams params;
case rsa:
ServerRSAParams params;
};
} ServerParams;
struct {
select (SignatureAlgorithm) {
case anonymous: struct { };
case rsa:
digitally-signed struct {
opaque md5_hash[16];
opaque sha_hash[20];
};
case dsa:
digitally-signed struct { digitally-signed struct {
opaque sha_hash[20]; opaque client_random[32];
}; opaque server_random[32];
}; ServerDHParams params;
} signed_params;
case rsa:
case dh_dss:
case dh_rsa:
struct {} ;
/* message is omitted for rsa, dh_dss, and dh_rsa */
}; };
} Signature; } ServerKeyExchange;
enum { enum {
rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4), rsa_sign(1), dss_sign(2), rsa_fixed_dh(3), dss_fixed_dh(4),
rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6), rsa_ephemeral_dh_RESERVED(5), dss_ephemeral_dh_RESERVED(6),
fortezza_dms_RESERVED(20), fortezza_dms_RESERVED(20),
(255) (255)
} ClientCertificateType; } ClientCertificateType;
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
struct { struct {
ClientCertificateType certificate_types<1..2^8-1>; ClientCertificateType certificate_types<1..2^8-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest; } CertificateRequest;
struct { } ServerHelloDone; struct { } ServerHelloDone;
A.4.3. Client Authentication and Key Exchange Messages A.4.3. Client Authentication and Key Exchange Messages
struct { struct {
select (KeyExchangeAlgorithm) { select (KeyExchangeAlgorithm) {
case rsa: EncryptedPreMasterSecret; case rsa:
case diffie_hellman: ClientDiffieHellmanPublic; EncryptedPreMasterSecret;
case dhe_dss:
case dhe_rsa:
case dh_dss:
case dh_rsa:
case dh_anon:
ClientDiffieHellmanPublic;
} exchange_keys; } exchange_keys;
} ClientKeyExchange; } ClientKeyExchange;
struct { struct {
ProtocolVersion client_version; ProtocolVersion client_version;
opaque random[46]; opaque random[46];
} } PreMasterSecret;
PreMasterSecret;
struct { struct {
public-key-encrypted PreMasterSecret pre_master_secret; public-key-encrypted PreMasterSecret pre_master_secret;
} EncryptedPreMasterSecret; } EncryptedPreMasterSecret;
enum { implicit, explicit } PublicValueEncoding; enum { implicit, explicit } PublicValueEncoding;
struct { struct {
select (PublicValueEncoding) { select (PublicValueEncoding) {
case implicit: struct {}; case implicit: struct {};
skipping to change at page 60, line 22 skipping to change at page 70, line 4
} EncryptedPreMasterSecret; } EncryptedPreMasterSecret;
enum { implicit, explicit } PublicValueEncoding; enum { implicit, explicit } PublicValueEncoding;
struct { struct {
select (PublicValueEncoding) { select (PublicValueEncoding) {
case implicit: struct {}; case implicit: struct {};
case explicit: opaque DH_Yc<1..2^16-1>; case explicit: opaque DH_Yc<1..2^16-1>;
} dh_public; } dh_public;
} ClientDiffieHellmanPublic; } ClientDiffieHellmanPublic;
struct { struct {
Signature signature; digitally-signed struct {
opaque handshake_messages[handshake_messages_length];
}
} CertificateVerify; } CertificateVerify;
A.4.4. Handshake Finalization Message A.4.4. Handshake Finalization Message
struct { struct {
opaque verify_data[12]; opaque verify_data[verify_data_length];
} Finished; } Finished;
A.5. The CipherSuite A.5. The Cipher Suite
The following values define the CipherSuite codes used in the client The following values define the cipher suite codes used in the client
hello and server hello messages. hello and server hello messages.
A CipherSuite defines a cipher specification supported in TLS Version A cipher suite defines a cipher specification supported in TLS
1.1. Version 1.2.
TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a TLS_NULL_WITH_NULL_NULL is specified and is the initial state of a
TLS connection during the first handshake on that channel, but must TLS connection during the first handshake on that channel, but MUST
not be negotiated, as it provides no more protection than an NOT be negotiated, as it provides no more protection than an
unsecured connection. unsecured connection.
CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 }; CipherSuite TLS_NULL_WITH_NULL_NULL = { 0x00,0x00 };
The following CipherSuite definitions require that the server provide The following CipherSuite definitions require that the server provide
an RSA certificate that can be used for key exchange. The server may an RSA certificate that can be used for key exchange. The server may
request either an RSA or a DSS signature-capable certificate in the request any signature-capable certificate in the certificate request
certificate request message. message.
CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 }; CipherSuite TLS_RSA_WITH_NULL_MD5 = { 0x00,0x01 };
CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 }; CipherSuite TLS_RSA_WITH_NULL_SHA = { 0x00,0x02 };
CipherSuite TLS_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 }; CipherSuite TLS_RSA_WITH_NULL_SHA256 = { 0x00,TBD1 };
CipherSuite TLS_RSA_WITH_RC4_128_SHA = { 0x00,0x05 }; CipherSuite TLS_RSA_WITH_RC4_128_MD5 = { 0x00,0x04 };
CipherSuite TLS_RSA_WITH_IDEA_CBC_SHA = { 0x00,0x07 }; CipherSuite TLS_RSA_WITH_RC4_128_SHA = { 0x00,0x05 };
CipherSuite TLS_RSA_WITH_DES_CBC_SHA = { 0x00,0x09 }; CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A };
CipherSuite TLS_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0A }; CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x2F };
CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x35 };
CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA256 = { 0x00,TBD2 };
CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA256 = { 0x00,TBD3 };
The following CipherSuite definitions are used for server- The following cipher suite definitions are used for server-
authenticated (and optionally client-authenticated) Diffie-Hellman. authenticated (and optionally client-authenticated) Diffie-Hellman.
DH denotes cipher suites in which the server's certificate contains DH denotes cipher suites in which the server's certificate contains
the Diffie-Hellman parameters signed by the certificate authority the Diffie-Hellman parameters signed by the certificate authority
(CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman (CA). DHE denotes ephemeral Diffie-Hellman, where the Diffie-Hellman
parameters are signed by a DSS or RSA certificate that has been parameters are signed by a a signature-capable certificate, which has
signed by the CA. The signing algorithm used is specified after the been signed by the CA. The signing algorithm used by the server is
DH or DHE parameter. The server can request an RSA or DSS specified after the DHE parameter. The server can request any
signature-capable certificate from the client for client signature-capable certificate from the client for client
authentication or it may request a Diffie-Hellman certificate. Any authentication or it may request a Diffie-Hellman certificate. Any
Diffie-Hellman certificate provided by the client must use the Diffie-Hellman certificate provided by the client must use the
parameters (group and generator) described by the server. parameters (group and generator) described by the server.
CipherSuite TLS_DH_DSS_WITH_DES_CBC_SHA = { 0x00,0x0C }; CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D };
CipherSuite TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x0D }; CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 };
CipherSuite TLS_DH_RSA_WITH_DES_CBC_SHA = { 0x00,0x0F }; CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 };
CipherSuite TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x10 }; CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 };
CipherSuite TLS_DHE_DSS_WITH_DES_CBC_SHA = { 0x00,0x12 }; CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00,0x30 };
CipherSuite TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA = { 0x00,0x13 }; CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x31 };
CipherSuite TLS_DHE_RSA_WITH_DES_CBC_SHA = { 0x00,0x15 }; CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00,0x32 };
CipherSuite TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA = { 0x00,0x16 }; CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00,0x33 };
CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA = { 0x00,0x36 };
The following cipher suites are used for completely anonymous CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x37 };
Diffie-Hellman communications in which neither party is CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA = { 0x00,0x38 };
authenticated. Note that this mode is vulnerable to man-in-the- CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA = { 0x00,0x39 };
middle attacks and is therefore deprecated. CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA256 = { 0x00, TBD4};
CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA256 = { 0x00, TBD5};
CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 }; CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 = { 0x00, TBD6};
CipherSuite TLS_DH_anon_WITH_DES_CBC_SHA = { 0x00,0x1A }; CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 = { 0x00, TBD7};
CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B }; CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA256 = { 0x00, TBD8};
CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA256 = { 0x00, TBD9};
When SSLv3 and TLS 1.0 were designed, the United States restricted CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA256 = { 0x00, TBDA};
the export of cryptographic software containing certain strong CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 = { 0x00, TBDB};
encryption algorithms. A series of cipher suites were designed to
operate at reduced key lengths in order to comply with those
regulations. Due to advances in computer performance, these
algorithms are now unacceptably weak, and export restrictions have
since been loosened. TLS 1.1 implementations MUST NOT negotiate
these cipher suites in TLS 1.1 mode. However, for backward
compatibility they may be offered in the ClientHello for use with TLS
1.0 or SSLv3-only servers. TLS 1.1 clients MUST check that the
server did not choose one of these cipher suites during the
handshake. These ciphersuites are listed below for informational
purposes and to reserve the numbers.
CipherSuite TLS_RSA_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x03 };
CipherSuite TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5 = { 0x00,0x06 };
CipherSuite TLS_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x08 };
CipherSuite TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0B };
CipherSuite TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x0E };
CipherSuite TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x11 };
CipherSuite TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x14 };
CipherSuite TLS_DH_anon_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x17 };
CipherSuite TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA = { 0x00,0x19 };
The following cipher suites were defined in [TLSKRB] and are included
here for completeness. See [TLSKRB] for details:
CipherSuite TLS_KRB5_WITH_DES_CBC_SHA = { 0x00,0x1E }: The following cipher suites are used for completely anonymous Diffie-
CipherSuite TLS_KRB5_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1F }; Hellman communications in which neither party is authenticated. Note
CipherSuite TLS_KRB5_WITH_RC4_128_SHA = { 0x00,0x20 }; that this mode is vulnerable to man-in-the-middle attacks. Using
CipherSuite TLS_KRB5_WITH_IDEA_CBC_SHA = { 0x00,0x21 }; this mode therefore is of limited use: These cipher suites MUST NOT
CipherSuite TLS_KRB5_WITH_DES_CBC_MD5 = { 0x00,0x22 }; be used by TLS 1.2 implementations unless the application layer has
CipherSuite TLS_KRB5_WITH_3DES_EDE_CBC_MD5 = { 0x00,0x23 }; specifically requested to allow anonymous key exchange. (Anonymous
CipherSuite TLS_KRB5_WITH_RC4_128_MD5 = { 0x00,0x24 }; key exchange may sometimes be acceptable, for example, to support
CipherSuite TLS_KRB5_WITH_IDEA_CBC_MD5 = { 0x00,0x25 }; opportunistic encryption when no set-up for authentication is in
place, or when TLS is used as part of more complex security protocols
that have other means to ensure authentication.)
The following exportable cipher suites were defined in [TLSKRB] and CipherSuite TLS_DH_anon_WITH_RC4_128_MD5 = { 0x00,0x18 };
are included here for completeness. TLS 1.1 implementations MUST NOT CipherSuite TLS_DH_anon_WITH_3DES_EDE_CBC_SHA = { 0x00,0x1B };
negotiate these cipher suites. CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00,0x34 };
CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00,0x3A };
CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA256 = { 0x00, TBDC};
CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA256 = { 0x00, TBDD};
CipherSuite TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA = { 0x00,0x26}; Note that using non-anonymous key exchange without actually verifying
CipherSuite TLS_KRB5_EXPORT_WITH_RC2_CBC_40_SHA = { 0x00,0x27}; the key exchange is essentially equivalent to anonymous key exchange,
CipherSuite TLS_KRB5_EXPORT_WITH_RC4_40_SHA = { 0x00,0x28}; and the same precautions apply. While non-anonymous key exchange
CipherSuite TLS_KRB5_EXPORT_WITH_DES_CBC_40_MD5 = { 0x00,0x29}; will generally involve a higher computational and communicational
CipherSuite TLS_KRB5_EXPORT_WITH_RC2_CBC_40_MD5 = { 0x00,0x2A}; cost than anonymous key exchange, it may be in the interest of
CipherSuite TLS_KRB5_EXPORT_WITH_RC4_40_MD5 = { 0x00,0x2B}; interoperability not to disable non-anonymous key exchange when the
application layer is allowing anonymous key exchange.
The following cipher suites were defined in [TLSAES] and are included New cipher suite values are assigned by IANA as described in Section
here for completeness. See [TLSAES] for details: 12.
CipherSuite TLS_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x2F }; Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are
CipherSuite TLS_DH_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x30 }; reserved to avoid collision with Fortezza-based cipher suites in SSL
CipherSuite TLS_DH_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x31 }; 3.
CipherSuite TLS_DHE_DSS_WITH_AES_128_CBC_SHA = { 0x00, 0x32 };
CipherSuite TLS_DHE_RSA_WITH_AES_128_CBC_SHA = { 0x00, 0x33 };
CipherSuite TLS_DH_anon_WITH_AES_128_CBC_SHA = { 0x00, 0x34 };
CipherSuite TLS_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x35 };
CipherSuite TLS_DH_DSS_WITH_AES_256_CBC_SHA = { 0x00, 0x36 };
CipherSuite TLS_DH_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x37 };
CipherSuite TLS_DHE_DSS_WITH_AES_256_CBC_SHA = { 0x00, 0x38 };
CipherSuite TLS_DHE_RSA_WITH_AES_256_CBC_SHA = { 0x00, 0x39 };
CipherSuite TLS_DH_anon_WITH_AES_256_CBC_SHA = { 0x00, 0x3A };
The cipher suite space is divided into three regions: A.6. The Security Parameters
1. Cipher suite values with first byte 0x00 (zero) through decimal These security parameters are determined by the TLS Handshake
191 (0xBF) inclusive are reserved for the IETF Standards Track Protocol and provided as parameters to the TLS Record Layer in order
protocols. to initialize a connection state. SecurityParameters includes:
2. Cipher suite values with first byte decimal 192 (0xC0) through enum { null(0), (255) } CompressionMethod;
decimal 254 (0xFE) inclusive are reserved for assignment for
non-Standards Track methods.
3. Cipher suite values with first byte 0xFF are reserved for enum { server, client } ConnectionEnd;
private use.
Additional information describing the role of IANA in the allocation enum { tls_prf_sha256 } PRFAlgorithm;
of cipher suite code points is described in Section 11.
Note: The cipher suite values { 0x00, 0x1C } and { 0x00, 0x1D } are enum { null, rc4, 3des, aes }
reserved to avoid collision with Fortezza-based cipher suites BulkCipherAlgorithm;
in SSL 3.
A.6. The Security Parameters enum { stream, block, aead } CipherType;
These security parameters are determined by the TLS Handshake enum { null, hmac_md5, hmac_sha, hmac_sha256, hmac_sha384,
Protocol and provided as parameters to the TLS Record Layer in hmac_sha512} MACAlgorithm;
order to initialize a connection state. SecurityParameters
includes:
enum { null(0), (255) } CompressionMethod; /* The algorithms specified in CompressionMethod,
BulkCipherAlgorithm, and MACAlgorithm may be added to. */
enum { server, client } ConnectionEnd; struct {
ConnectionEnd entity;
PRFAlgorithm prf_algorithm;
BulkCipherAlgorithm bulk_cipher_algorithm;
CipherType cipher_type;
uint8 enc_key_length;
uint8 block_length;
uint8 fixed_iv_length;
uint8 record_iv_length;
MACAlgorithm mac_algorithm;
uint8 mac_length;
uint8 mac_key_length;
CompressionMethod compression_algorithm;
opaque master_secret[48];
opaque client_random[32];
opaque server_random[32];
} SecurityParameters;
enum { null, rc4, rc2, des, 3des, des40, aes, idea } A.7. Changes to RFC 4492
BulkCipherAlgorithm;
enum { stream, block } CipherType; RFC 4492 [TLSECC] adds Elliptic Curve cipher suites to TLS. This
document changes some of the structures used in that document. This
section details the required changes for implementors of both RFC
4492 and TLS 1.2. Implementors of TLS 1.2 who are not implementing
RFC 4492 do not need to read this section.
enum { null, md5, sha } MACAlgorithm; This document adds a "signature_algorithm" field to the digitally-
signed element in order to identify the signature and digest
algorithms used to create a signature. This change applies to digital
signatures formed using ECDSA as well, thus allowing ECDSA signatures
to be used and digest algorithms other than SHA-1, provided such use
is compatible with the certificate and any restrictions imposed by
future revisions of [PKIX].
/* The algorithms specified in CompressionMethod, As described in Sections 7.4.2 and 7.4.6, the restrictions on the
BulkCipherAlgorithm, and MACAlgorithm may be added to. */ signature algorithms used to sign certificates are no longer tied to
struct { the cipher suite (when used by the server) or the
ConnectionEnd entity; ClientCertificateType (when used by the client). Thus, the
BulkCipherAlgorithm bulk_cipher_algorithm; restrictions on the algorithm used to sign certificates specified in
CipherType cipher_type; Sections 2 and 3 of RFC 4492 are also relaxed. As in this document
uint8 key_size; the restrictions on the keys in the end-entity certificate remain.
uint8 key_material_length;
MACAlgorithm mac_algorithm;
uint8 hash_size;
CompressionMethod compression_algorithm;
opaque master_secret[48];
opaque client_random[32];
opaque server_random[32];
} SecurityParameters;
Appendix B. Glossary Appendix B. Glossary
Advanced Encryption Standard (AES) Advanced Encryption Standard (AES)
AES is a widely used symmetric encryption algorithm. AES is a AES is a widely used symmetric encryption algorithm. AES is a
block cipher with a 128, 192, or 256 bit keys and a 16 byte block block cipher with a 128, 192, or 256 bit keys and a 16 byte block
size. [AES] TLS currently only supports the 128 and 256 bit key size. [AES] TLS currently only supports the 128 and 256 bit key
sizes. sizes.
application protocol application protocol
An application protocol is a protocol that normally layers An application protocol is a protocol that normally layers
directly on top of the transport layer (e.g., TCP/IP). Examples directly on top of the transport layer (e.g., TCP/IP). Examples
include HTTP, TELNET, FTP, and SMTP. include HTTP, TELNET, FTP, and SMTP.
asymmetric cipher asymmetric cipher
See public key cryptography. See public key cryptography.
authenticated encryption with additional data (AEAD)
A symmetric encryption algorithm that simultaneously provides
confidentiality and message integrity.
authentication authentication
Authentication is the ability of one entity to determine the Authentication is the ability of one entity to determine the
identity of another entity. identity of another entity.
block cipher block cipher
A block cipher is an algorithm that operates on plaintext in A block cipher is an algorithm that operates on plaintext in
groups of bits, called blocks. 64 bits is a common block size. groups of bits, called blocks. 64 bits is a common block size.
bulk cipher bulk cipher
A symmetric encryption algorithm used to encrypt large quantities A symmetric encryption algorithm used to encrypt large quantities
of data. of data.
cipher block chaining (CBC) cipher block chaining (CBC)
CBC is a mode in which every plaintext block encrypted with a CBC is a mode in which every plaintext block encrypted with a
block cipher is first exclusive-ORed with the previous ciphertext block cipher is first exclusive-ORed with the previous ciphertext
block (or, in the case of the first block, with the initialization block (or, in the case of the first block, with the initialization
vector). For decryption, every block is first decrypted, then vector). For decryption, every block is first decrypted, then
exclusive-ORed with the previous ciphertext block (or IV). exclusive-ORed with the previous ciphertext block (or IV).
certificate certificate
As part of the X.509 protocol (a.k.a. ISO Authentication As part of the X.509 protocol (a.k.a. ISO Authentication
framework), certificates are assigned by a trusted Certificate framework), certificates are assigned by a trusted Certificate
Authority and provide a strong binding between a party's identity Authority and provide a strong binding between a party's identity
or some other attributes and its public key. or some other attributes and its public key.
client client
The application entity that initiates a TLS connection to a The application entity that initiates a TLS connection to a
server. This may or may not imply that the client initiated the server. This may or may not imply that the client initiated the
underlying transport connection. The primary operational underlying transport connection. The primary operational
difference between the server and client is that the server is difference between the server and client is that the server is
generally authenticated, while the client is only optionally generally authenticated, while the client is only optionally
authenticated. authenticated.
client write key client write key
The key used to encrypt data written by the client. The key used to encrypt data written by the client.
client write MAC secret client write MAC key
The secret data used to authenticate data written by the client. The secret data used to authenticate data written by the client.
connection connection
A connection is a transport (in the OSI layering model definition) A connection is a transport (in the OSI layering model definition)
that provides a suitable type of service. For TLS, such that provides a suitable type of service. For TLS, such
connections are peer-to-peer relationships. The connections are connections are peer-to-peer relationships. The connections are
transient. Every connection is associated with one session. transient. Every connection is associated with one session.
Data Encryption Standard Data Encryption Standard
DES is a very widely used symmetric encryption algorithm. DES is DES is a very widely used symmetric encryption algorithm. DES is a
a block cipher with a 56 bit key and an 8 byte block size. Note block cipher with a 56 bit key and an 8 byte block size. Note that
that in TLS, for key generation purposes, DES is treated as having in TLS, for key generation purposes, DES is treated as having an 8
an 8 byte key length (64 bits), but it still only provides 56 bits byte key length (64 bits), but it still only provides 56 bits of
of protection. (The low bit of each key byte is presumed to be protection. (The low bit of each key byte is presumed to be set to
set to produce odd parity in that key byte.) DES can also be produce odd parity in that key byte.) DES can also be operated in
operated in a mode where three independent keys and three a mode where three independent keys and three encryptions are used
encryptions are used for each block of data; this uses 168 bits of for each block of data; this uses 168 bits of key (24 bytes in the
key (24 bytes in the TLS key generation method) and provides the TLS key generation method) and provides the equivalent of 112 bits
equivalent of 112 bits of security. [DES], [3DES] of security. [DES], [3DES]
Digital Signature Standard (DSS) Digital Signature Standard (DSS)
A standard for digital signing, including the Digital Signing A standard for digital signing, including the Digital Signing
Algorithm, approved by the National Institute of Standards and Algorithm, approved by the National Institute of Standards and
Technology, defined in NIST FIPS PUB 186, "Digital Signature Technology, defined in NIST FIPS PUB 186, "Digital Signature
Standard," published May 1994 by the U.S. Dept. of Commerce. Standard", published May, 1994 by the U.S. Dept. of Commerce.
[DSS] [DSS]
digital signatures digital signatures
Digital signatures utilize public key cryptography and one-way Digital signatures utilize public key cryptography and one-way
hash functions to produce a signature of the data that can be hash functions to produce a signature of the data that can be
authenticated, and is difficult to forge or repudiate. authenticated, and is difficult to forge or repudiate.
handshake handshake
An initial negotiation between client and server that establishes An initial negotiation between client and server that establishes
the parameters of their transactions. the parameters of their transactions.
Initialization Vector (IV) Initialization Vector (IV)
When a block cipher is used in CBC mode, the initialization vector When a block cipher is used in CBC mode, the initialization vector
is exclusive-ORed with the first plaintext block prior to is exclusive-ORed with the first plaintext block prior to
encryption. encryption.
IDEA
A 64-bit block cipher designed by Xuejia Lai and James Massey.
[IDEA]
Message Authentication Code (MAC) Message Authentication Code (MAC)
A Message Authentication Code is a one-way hash computed from a A Message Authentication Code is a one-way hash computed from a
message and some secret data. It is difficult to forge without message and some secret data. It is difficult to forge without
knowing the secret data. Its purpose is to detect if the message knowing the secret data. Its purpose is to detect if the message
has been altered. has been altered.
master secret master secret
Secure secret data used for generating encryption keys, MAC Secure secret data used for generating encryption keys, MAC
secrets, and IVs. secrets, and IVs.
MD5 MD5
MD5 is a secure hashing function that converts an arbitrarily long MD5 is a secure hashing function that converts an arbitrarily long
data stream into a digest of fixed size (16 bytes). [MD5] data stream into a hash of fixed size (16 bytes). [MD5]
public key cryptography public key cryptography
A class of cryptographic techniques employing two-key ciphers. A class of cryptographic techniques employing two-key ciphers.
Messages encrypted with the public key can only be decrypted with Messages encrypted with the public key can only be decrypted with
the associated private key. Conversely, messages signed with the the associated private key. Conversely, messages signed with the
private key can be verified with the public key. private key can be verified with the public key.
one-way hash function one-way hash function
A one-way transformation that converts an arbitrary amount of data A one-way transformation that converts an arbitrary amount of data
into a fixed-length hash. It is computationally hard to reverse into a fixed-length hash. It is computationally hard to reverse
the transformation or to find collisions. MD5 and SHA are the transformation or to find collisions. MD5 and SHA are examples
examples of one-way hash functions. of one-way hash functions.
RC2
A block cipher developed by Ron Rivest at RSA Data Security, Inc.
[RSADSI] described in [RC2].
RC4 RC4
A stream cipher invented by Ron Rivest. A compatible cipher is A stream cipher invented by Ron Rivest. A compatible cipher is
described in [SCH]. described in [SCH].
RSA RSA
A very widely used public-key algorithm that can be used for A very widely used public-key algorithm that can be used for
either encryption or digital signing. [RSA] either encryption or digital signing. [RSA]
server server
The server is the application entity that responds to requests for The server is the application entity that responds to requests for
connections from clients. See also under client. connections from clients. See also under client.
session session
A TLS session is an association between a client and a server. A TLS session is an association between a client and a server.
Sessions are created by the handshake protocol. Sessions define a Sessions are created by the handshake protocol. Sessions define a
set of cryptographic security parameters that can be shared among set of cryptographic security parameters that can be shared among
multiple connections. Sessions are used to avoid the expensive multiple connections. Sessions are used to avoid the expensive
negotiation of new security parameters for each connection. negotiation of new security parameters for each connection.
session identifier session identifier
A session identifier is a value generated by a server that A session identifier is a value generated by a server that
identifies a particular session. identifies a particular session.
server write key server write key
The key used to encrypt data written by the server. The key used to encrypt data written by the server.
server write MAC secret server write MAC key
The secret data used to authenticate data written by the server. The secret data used to authenticate data written by the server.
SHA SHA
The Secure Hash Algorithm is defined in FIPS PUB 180-2. It The Secure Hash Algorithm is defined in FIPS PUB 180-2. It
produces a 20-byte output. Note that all references to SHA produces a 20-byte output. Note that all references to SHA
actually use the modified SHA-1 algorithm. [SHA] actually use the modified SHA-1 algorithm. [SHA]
SHA-256
The 256-bit Secure Hash Algorithm is defined in FIPS PUB 180-2. It
produces a 32-byte output.
SSL SSL
Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on Netscape's Secure Socket Layer protocol [SSL3]. TLS is based on
SSL Version 3.0 SSL Version 3.0
stream cipher stream cipher
An encryption algorithm that converts a key into a An encryption algorithm that converts a key into a
cryptographically strong keystream, which is then exclusive-ORed cryptographically strong keystream, which is then exclusive-ORed
with the plaintext. with the plaintext.
symmetric cipher symmetric cipher
See bulk cipher. See bulk cipher.
Transport Layer Security (TLS) Transport Layer Security (TLS)
This protocol; also, the Transport Layer Security working group of This protocol; also, the Transport Layer Security working group of
the Internet Engineering Task Force (IETF). See "Comments" at the the Internet Engineering Task Force (IETF). See "Comments" at the
end of this document. end of this document.
Appendix C. CipherSuite Definitions Appendix C. Cipher Suite Definitions
CipherSuite Key Exchange Cipher Hash Cipher Suite Key Cipher Mac
Exchange
TLS_NULL_WITH_NULL_NULL NULL NULL NULL TLS_NULL_WITH_NULL_NULL NULL NULL NULL
TLS_RSA_WITH_NULL_MD5 RSA NULL MD5 TLS_RSA_WITH_NULL_MD5 RSA NULL MD5
TLS_RSA_WITH_NULL_SHA RSA NULL SHA TLS_RSA_WITH_NULL_SHA RSA NULL SHA
TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5 TLS_RSA_WITH_NULL_SHA256 RSA NULL SHA256
TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA TLS_RSA_WITH_RC4_128_MD5 RSA RC4_128 MD5
TLS_RSA_WITH_IDEA_CBC_SHA RSA IDEA_CBC SHA TLS_RSA_WITH_RC4_128_SHA RSA RC4_128 SHA
TLS_RSA_WITH_DES_CBC_SHA RSA DES_CBC SHA TLS_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA RSA 3DES_EDE_CBC SHA TLS_RSA_WITH_AES_128_CBC_SHA RSA AES_128_CBC SHA
TLS_DH_DSS_WITH_DES_CBC_SHA DH_DSS DES_CBC SHA TLS_RSA_WITH_AES_256_CBC_SHA RSA AES_256_CBC SHA
TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA TLS_RSA_WITH_AES_128_CBC_SHA256 RSA AES_128_CBC SHA256
TLS_DH_RSA_WITH_DES_CBC_SHA DH_RSA DES_CBC SHA TLS_RSA_WITH_AES_256_CBC_SHA256 RSA AES_256_CBC SHA256
TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA DH_DSS 3DES_EDE_CBC SHA
TLS_DHE_DSS_WITH_DES_CBC_SHA DHE_DSS DES_CBC SHA TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA DH_RSA 3DES_EDE_CBC SHA
TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA DHE_DSS 3DES_EDE_CBC SHA
TLS_DHE_RSA_WITH_DES_CBC_SHA DHE_RSA DES_CBC SHA TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA
TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA DHE_RSA 3DES_EDE_CBC SHA TLS_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5
TLS_DH_anon_WITH_RC4_128_MD5 DH_anon RC4_128 MD5 TLS_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA
TLS_DH_anon_WITH_DES_CBC_SHA DH_anon DES_CBC SHA TLS_DH_DSS_WITH_AES_128_CBC_SHA DH_DSS AES_128_CBC SHA
TLS_DH_anon_WITH_3DES_EDE_CBC_SHA DH_anon 3DES_EDE_CBC SHA TLS_DH_RSA_WITH_AES_128_CBC_SHA DH_RSA AES_128_CBC SHA
TLS_DHE_DSS_WITH_AES_128_CBC_SHA DHE_DSS AES_128_CBC SHA
TLS_DHE_RSA_WITH_AES_128_CBC_SHA DHE_RSA AES_128_CBC SHA
TLS_DH_anon_WITH_AES_128_CBC_SHA DH_anon AES_128_CBC SHA
TLS_DH_DSS_WITH_AES_256_CBC_SHA DH_DSS AES_256_CBC SHA
TLS_DH_RSA_WITH_AES_256_CBC_SHA DH_RSA AES_256_CBC SHA
TLS_DHE_DSS_WITH_AES_256_CBC_SHA DHE_DSS AES_256_CBC SHA
TLS_DHE_RSA_WITH_AES_256_CBC_SHA DHE_RSA AES_256_CBC SHA
TLS_DH_anon_WITH_AES_256_CBC_SHA DH_anon AES_256_CBC SHA
TLS_DH_DSS_WITH_AES_128_CBC_SHA256 DH_DSS AES_128_CBC SHA256
TLS_DH_RSA_WITH_AES_128_CBC_SHA256 DH_RSA AES_128_CBC SHA256
TLS_DHE_DSS_WITH_AES_128_CBC_SHA256 DHE_DSS AES_128_CBC SHA256
TLS_DHE_RSA_WITH_AES_128_CBC_SHA256 DHE_RSA AES_128_CBC SHA256
TLS_DH_anon_WITH_AES_128_CBC_SHA256 DH_anon AES_128_CBC SHA256
TLS_DH_DSS_WITH_AES_256_CBC_SHA256 DH_DSS AES_256_CBC SHA256
TLS_DH_RSA_WITH_AES_256_CBC_SHA256 DH_RSA AES_256_CBC SHA256
TLS_DHE_DSS_WITH_AES_256_CBC_SHA256 DHE_DSS AES_256_CBC SHA256
TLS_DHE_RSA_WITH_AES_256_CBC_SHA256 DHE_RSA AES_256_CBC SHA256
TLS_DH_anon_WITH_AES_256_CBC_SHA256 DH_anon AES_256_CBC SHA256
Key Key Expanded IV Block
Exchange Cipher Type Material Key Material Size Size
Algorithm Description Key size limit
DHE_DSS Ephemeral DH with DSS signatures None NULL Stream 0 0 0 N/A
DHE_RSA Ephemeral DH with RSA signatures None RC4_128 Stream 16 16 0 N/A
DH_anon Anonymous DH, no signatures None 3DES_EDE_CBC Block 24 24 8 8
DH_DSS DH with DSS-based certificates None AES_128_CBC Block 16 16 16 16
DH_RSA DH with RSA-based certificates None AES_256_CBC Block 32 32 16 16
RSA = none
NULL No key exchange N/A
RSA RSA key exchange None
Key Expanded IV Block
Cipher Type Material Key Material Size Size
NULL Stream 0 0 0 N/A MAC Algorithm mac_length mac_key_length
IDEA_CBC Block 16 16 8 8
RC2_CBC_40 Block 5 16 8 8 NULL N/A 0 0
RC4_40 Stream 5 16 0 N/A MD5 HMAC-MD5 16 16
RC4_128 Stream 16 16 0 N/A SHA HMAC-SHA1 20 20
DES40_CBC Block 5 8 8 8 SHA256 HMAC-SHA256 32 32
DES_CBC Block 8 8 8 8
3DES_EDE_CBC Block 24 24 8 8
Type Type
Indicates whether this is a stream cipher or a block cipher Indicates whether this is a stream cipher or a block cipher
running in CBC mode. running in CBC mode.
Key Material Key Material
The number of bytes from the key_block that are used for The number of bytes from the key_block that are used for
generating the write keys. generating the write keys.
Expanded Key Material Expanded Key Material
The number of bytes actually fed into the encryption algorithm. The number of bytes actually fed into the encryption algorithm.
IV Size IV Size
The amount of data needed to be generated for the initialization The amount of data needed to be generated for the initialization
vector. Zero for stream ciphers; equal to the block size for vector. Zero for stream ciphers; equal to the block size for block
block ciphers. ciphers (this is equal to SecurityParameters.record_iv_length).
Block Size Block Size
The amount of data a block cipher enciphers in one chunk; a block The amount of data a block cipher enciphers in one chunk; a block
cipher running in CBC mode can only encrypt an even multiple of cipher running in CBC mode can only encrypt an even multiple of
its block size. its block size.
Hash Hash Padding
function Size Size
NULL 0 0
MD5 16 48
SHA 20 40
Appendix D. Implementation Notes Appendix D. Implementation Notes
The TLS protocol cannot prevent many common security mistakes. This The TLS protocol cannot prevent many common security mistakes. This
section provides several recommendations to assist implementors. section provides several recommendations to assist implementors.
D.1. Random Number Generation and Seeding D.1 Random Number Generation and Seeding
TLS requires a cryptographically secure pseudorandom number generator TLS requires a cryptographically secure pseudorandom number generator
(PRNG). Care must be taken in designing and seeding PRNGs. PRNGs (PRNG). Care must be taken in designing and seeding PRNGs. PRNGs
based on secure hash operations, most notably MD5 and/or SHA, are based on secure hash operations, most notably SHA-1, are acceptable,
acceptable, but cannot provide more security than the size of the but cannot provide more security than the size of the random number
random number generator state. (For example, MD5-based PRNGs usually generator state.
provide 128 bits of state.)
To estimate the amount of seed material being produced, add the To estimate the amount of seed material being produced, add the
number of bits of unpredictable information in each seed byte. For number of bits of unpredictable information in each seed byte. For
example, keystroke timing values taken from a PC compatible's 18.2 Hz example, keystroke timing values taken from a PC compatible's 18.2 Hz
timer provide 1 or 2 secure bits each, even though the total size of timer provide 1 or 2 secure bits each, even though the total size of
the counter value is 16 bits or more. Seeding a 128-bit PRNG would the counter value is 16 bits or more. Seeding a 128-bit PRNG would
thus require approximately 100 such timer values. thus require approximately 100 such timer values.
[RANDOM] provides guidance on the generation of random values. [RANDOM] provides guidance on the generation of random values.
D.2 Certificates and Authentication D.2 Certificates and Authentication
Implementations are responsible for verifying the integrity of Implementations are responsible for verifying the integrity of
certificates and should generally support certificate revocation certificates and should generally support certificate revocation
messages. Certificates should always be verified to ensure proper messages. Certificates should always be verified to ensure proper
signing by a trusted Certificate Authority (CA). The selection and signing by a trusted Certificate Authority (CA). The selection and
addition of trusted CAs should be done very carefully. Users should addition of trusted CAs should be done very carefully. Users should
be able to view information about the certificate and root CA. be able to view information about the certificate and root CA.
D.3 CipherSuites D.3 Cipher Suites
TLS supports a range of key sizes and security levels, including some TLS supports a range of key sizes and security levels, including some
that provide no or minimal security. A proper implementation will that provide no or minimal security. A proper implementation will
probably not support many cipher suites. For example, 40-bit probably not support many cipher suites. For instance, anonymous
encryption is easily broken, so implementations requiring strong Diffie-Hellman is strongly discouraged because it cannot prevent man-
security should not allow 40-bit keys. Similarly, anonymous Diffie- in-the-middle attacks. Applications should also enforce minimum and
Hellman is strongly discouraged because it cannot prevent man-in- maximum key sizes. For example, certificate chains containing 512-bit
the-middle attacks. Applications should also enforce minimum and RSA keys or signatures are not appropriate for high-security
maximum key sizes. For example, certificate chains containing 512-
bit RSA keys or signatures are not appropriate for high-security
applications. applications.
Appendix E. Backward Compatibility with SSL D.4 Implementation Pitfalls
For historical reasons and in order to avoid a profligate consumption Implementation experience has shown that certain parts of earlier TLS
of reserved port numbers, application protocols that are secured by specifications are not easy to understand, and have been a source of
TLS 1.1, TLS 1.0, SSL 3.0, and SSL 2.0 all frequently share the same interoperability and security problems. Many of these areas have been
connection port. For example, the https protocol (HTTP secured by clarified in this document, but this appendix contains a short list
SSL or TLS) uses port 443 regardless of which security protocol it is of the most important things that require special attention from
using. Thus, some mechanism must be determined to distinguish and implementors.
negotiate among the various protocols.
TLS versions 1.1 and 1.0, and SSL 3.0 are very similar; thus, TLS protocol issues:
supporting both is easy. TLS clients who wish to negotiate with such
older servers SHOULD send client hello messages using the SSL 3.0
record format and client hello structure, sending {3, 2} for the
version field to note that they support TLS 1.1. If the server
supports only TLS 1.0 or SSL 3.0, it will respond with a downrev 3.0
server hello; if it supports TLS 1.1 it will respond with a TLS 1.1
server hello. The negotiation then proceeds as appropriate for the
negotiated protocol.
Similarly, a TLS 1.1 server that wishes to interoperate with TLS 1.0 - Do you correctly handle handshake messages that are fragmented
or SSL 3.0 clients SHOULD accept SSL 3.0 client hello messages and to multiple TLS records (see Section 6.2.1)? Including corner
respond with a SSL 3.0 server hello if an SSL 3.0 client hello with a cases like a ClientHello that is split to several small
version field of {3, 0} is received, denoting that this client does fragments? Do you fragment handshake messages that exceed the
not support TLS. Similarly, if a SSL 3.0 or TLS 1.0 hello with a maximum fragment size? In particular, the certificate and
version field of {3, 1} is received, the server SHOULD respond with a certificate request handshake messages can be large enough to
TLS 1.0 hello with a version field of {3, 1}. require fragmentation.
- Do you ignore the TLS record layer version number in all TLS
records before ServerHello (see Appendix E.1)?
- Do you handle TLS extensions in ClientHello correctly,
including omitting the extensions field completely?
- Do you support renegotiation, both client and server initiated?
While renegotiation is an optional feature, supporting
it is highly recommended.
- When the server has requested a client certificate, but no
suitable certificate is available, do you correctly send
an empty Certificate message, instead of omitting the whole
message (see Section 7.4.6)?
Cryptographic details:
- In RSA-encrypted Premaster Secret, do you correctly send and
verify the version number? When an error is encountered, do
you continue the handshake to avoid the Bleichenbacher
attack (see Section 7.4.7.1)?
- What countermeasures do you use to prevent timing attacks against
RSA decryption and signing operations (see Section 7.4.7.1)?
- When verifying RSA signatures, do you accept both NULL and
missing parameters (see Section 4.7)? Do you verify that the
RSA padding doesn't have additional data after the hash value?
[FI06]
- When using Diffie-Hellman key exchange, do you correctly strip
leading zero bytes from the negotiated key (see Section 8.1.2)?
- Does your TLS client check that the Diffie-Hellman parameters
sent by the server are acceptable (see Section F.1.1.3)?
- How do you generate unpredictable IVs for CBC mode ciphers
(see Section 6.2.3.2)?
- Do you accept long CBC mode padding (up to 255 bytes; see
Section 6.2.3.2)?
- How do you address CBC mode timing attacks (Section 6.2.3.2)?
- Do you use a strong and, most importantly, properly seeded
random number generator (see Appendix D.1) for generating the
premaster secret (for RSA key exchange), Diffie-Hellman private
values, the DSA "k" parameter, and other security-critical
values?
Appendix E. Backward Compatibility
E.1 Compatibility with TLS 1.0/1.1 and SSL 3.0
Since there are various versions of TLS (1.0, 1.1, 1.2, and any
future versions) and SSL (2.0 and 3.0), means are needed to negotiate
the specific protocol version to use. The TLS protocol provides a
built-in mechanism for version negotiation so as not to bother other
protocol components with the complexities of version selection.
TLS versions 1.0, 1.1, and 1.2, and SSL 3.0 are very similar, and use
compatible ClientHello messages; thus, supporting all of them is
relatively easy. Similarly, servers can easily handle clients trying
to use future versions of TLS as long as the ClientHello format
remains compatible, and the client support the highest protocol
version available in the server.
A TLS 1.2 client who wishes to negotiate with such older servers will
send a normal TLS 1.2 ClientHello, containing { 3, 3 } (TLS 1.2) in
ClientHello.client_version. If the server does not support this
version, it will respond with ServerHello containing an older version
number. If the client agrees to use this version, the negotiation
will proceed as appropriate for the negotiated protocol.
If the version chosen by the server is not supported by the client
(or not acceptable), the client MUST send a "protocol_version" alert
message and close the connection.
If a TLS server receives a ClientHello containing a version number
greater than the highest version supported by the server, it MUST
reply according to the highest version supported by the server.
A TLS server can also receive a ClientHello containing version number
smaller than the highest supported version. If the server wishes to
negotiate with old clients, it will proceed as appropriate for the
highest version supported by the server that is not greater than
ClientHello.client_version. For example, if the server supports TLS
1.0, 1.1, and 1.2, and client_version is TLS 1.0, the server will
proceed with a TLS 1.0 ServerHello. If server supports (or is willing
to use) only versions greater than client_version, it MUST send a
"protocol_version" alert message and close the connection.
Whenever a client already knows the highest protocol known to a Whenever a client already knows the highest protocol known to a
server (for example, when resuming a session), it SHOULD initiate the server (for example, when resuming a session), it SHOULD initiate the
connection in that native protocol. connection in that native protocol.
TLS 1.1 clients that support SSL Version 2.0 servers MUST send SSL Note: some server implementations are known to implement version
Version 2.0 client hello messages [SSL2]. TLS servers SHOULD accept negotiation incorrectly. For example, there are buggy TLS 1.0 servers
either client hello format if they wish to support SSL 2.0 clients on that simply close the connection when the client offers a version
the same connection port. The only deviations from the Version 2.0 newer than TLS 1.0. Also, it is known that some servers will refuse
specification are the ability to specify a version with a value of connection if any TLS extensions are included in ClientHello.
three and the support for more ciphering types in the CipherSpec. Interoperability with such buggy servers is a complex topic beyond
the scope of this document, and may require multiple connection
Warning: The ability to send Version 2.0 client hello messages will be attempts by the client.
phased out with all due haste. Implementors SHOULD make every
effort to move forward as quickly as possible. Version 3.0
provides better mechanisms for moving to newer versions.
The following cipher specifications are carryovers from SSL
Version 2.0. These are assumed to use RSA for key exchange and
authentication.
V2CipherSpec TLS_RC4_128_WITH_MD5 = { 0x01,0x00,0x80 }; Earlier versions of the TLS specification were not fully clear on
V2CipherSpec TLS_RC4_128_EXPORT40_WITH_MD5 = { 0x02,0x00,0x80 }; what the record layer version number (TLSPlaintext.version) should
V2CipherSpec TLS_RC2_CBC_128_CBC_WITH_MD5 = { 0x03,0x00,0x80 }; contain when sending ClientHello (i.e., before it is known which
V2CipherSpec TLS_RC2_CBC_128_CBC_EXPORT40_WITH_MD5 version of the protocol will be employed). Thus, TLS servers
= { 0x04,0x00,0x80 }; compliant with this specification MUST accept any value {03,XX} as
V2CipherSpec TLS_IDEA_128_CBC_WITH_MD5 = { 0x05,0x00,0x80 }; the record layer version number for ClientHello.
V2CipherSpec TLS_DES_64_CBC_WITH_MD5 = { 0x06,0x00,0x40 };
V2CipherSpec TLS_DES_192_EDE3_CBC_WITH_MD5 = { 0x07,0x00,0xC0 };
Cipher specifications native to TLS can be included in Version TLS clients that wish to negotiate with older servers MAY send any
2.0 client hello messages using the syntax below. Any value {03,XX} as the record layer version number. Typical values
V2CipherSpec element with its first byte equal to zero will be would be {03,00}, the lowest version number supported by the client,
ignored by Version 2.0 servers. Clients sending any of the above and the value of ClientHello.client_version. No single value will
V2CipherSpecs SHOULD also include the TLS equivalent (see guarantee interoperability with all old servers, but this is a
Appendix A.5): complex topic beyond the scope of this document.
V2CipherSpec (see TLS name) = { 0x00, CipherSuite }; E.2 Compatibility with SSL 2.0
Note: TLS 1.1 clients may generate the SSLv2 EXPORT cipher suites in TLS 1.2 clients that wish to support SSL 2.0 servers MUST send
handshakes for backward compatibility but MUST NOT negotiate them version 2.0 CLIENT-HELLO messages defined in [SSL2]. The message MUST
in TLS 1.1 mode. contain the same version number as would be used for ordinary
ClientHello, and MUST encode the supported TLS cipher suites in the
CIPHER-SPECS-DATA field as described below.
E.1. Version 2 Client Hello Warning: The ability to send version 2.0 CLIENT-HELLO messages will
be phased out with all due haste, since the newer ClientHello format
provides better mechanisms for moving to newer versions and
negotiating extensions. TLS 1.2 clients SHOULD NOT support SSL 2.0.
The Version 2.0 client hello message is presented below using this However, even TLS servers that do not support SSL 2.0 MAY accept
document's presentation model. The true definition is still assumed version 2.0 CLIENT-HELLO messages. The message is presented below in
to be the SSL Version 2.0 specification. Note that this message MUST sufficient detail for TLS server implementors; the true definition is
be sent directly on the wire, not wrapped as an SSLv3 record still assumed to be [SSL2].
uint8 V2CipherSpec[3]; For negotiation purposes, 2.0 CLIENT-HELLO is interpreted the same
way as a ClientHello with a "null" compression method and no
extensions. Note that this message MUST be sent directly on the wire,
not wrapped as a TLS record. For the purposes of calculating Finished
and CertificateVerify, the msg_length field is not considered to be a
part of the handshake message.
struct { uint8 V2CipherSpec[3];
uint16 msg_length; struct {
uint8 msg_type; uint16 msg_length;
Version version; uint8 msg_type;
uint16 cipher_spec_length; Version version;
uint16 session_id_length; uint16 cipher_spec_length;
uint16 challenge_length; uint16 session_id_length;
V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length]; uint16 challenge_length;
opaque session_id[V2ClientHello.session_id_length]; V2CipherSpec cipher_specs[V2ClientHello.cipher_spec_length];
opaque challenge[V2ClientHello.challenge_length; opaque session_id[V2ClientHello.session_id_length];
} V2ClientHello; opaque challenge[V2ClientHello.challenge_length;
} V2ClientHello;
msg_length msg_length
This field is the length of the following data in bytes. The high The highest bit MUST be 1; the remaining bits contain the length
bit MUST be 1 and is not part of the length. of the following data in bytes.
msg_type msg_type
This field, in conjunction with the version field, identifies a This field, in conjunction with the version field, identifies a
version 2 client hello message. The value SHOULD be one (1). version 2 client hello message. The value MUST be one (1).
version version
The highest version of the protocol supported by the client Equal to ClientHello.client_version.
(equals ProtocolVersion.version; see Appendix A.1).
cipher_spec_length cipher_spec_length
This field is the total length of the field cipher_specs. It This field is the total length of the field cipher_specs. It
cannot be zero and MUST be a multiple of the V2CipherSpec length cannot be zero and MUST be a multiple of the V2CipherSpec length
(3). (3).
session_id_length session_id_length
This field MUST have a value of zero. This field MUST have a value of zero for a client that claims to
support TLS 1.2.
challenge_length challenge_length
The length in bytes of the client's challenge to the server to The length in bytes of the client's challenge to the server to
authenticate itself. When using the SSLv2 backward compatible authenticate itself. Historically, permissible values are between
handshake the client MUST use a 32-byte challenge. 16 and 32 bytes inclusive. When using the SSLv2 backward
compatible handshake the client SHOULD use a 32 byte challenge.
cipher_specs cipher_specs
This is a list of all CipherSpecs the client is willing and able This is a list of all CipherSpecs the client is willing and able
to use. There MUST be at least one CipherSpec acceptable to the to use. In addition to the 2.0 cipher specs defined in [SSL2],
server. this includes the TLS cipher suites normally sent in
ClientHello.cipher_suites, each cipher suite prefixed by a zero
byte. For example, TLS cipher suite {0x00,0x0A} would be sent as
{0x00,0x00,0x0A}.
session_id session_id
This field MUST be empty. This field MUST be empty.
challenge The client challenge to the server for the server to challenge
identify itself is a (nearly) arbitrary-length random. The TLS Corresponds to ClientHello.random. If the challenge length is less
server will right-justify the challenge data to become the than 32, the TLS server will pad the data with leading (note: not
ClientHello.random data (padded with leading zeroes, if trailing) zero bytes to make it 32 bytes long.
necessary), as specified in this protocol specification. If the
length of the challenge is greater than 32 bytes, only the last 32
bytes are used. It is legitimate (but not necessary) for a V3
server to reject a V2 ClientHello that has fewer than 16 bytes of
challenge data.
Note: Requests to resume a TLS session MUST use a TLS client Note: Requests to resume a TLS session MUST use a TLS client hello.
hello.
E.2. Avoiding Man-in-the-Middle Version Rollback E.3. Avoiding Man-in-the-Middle Version Rollback
When TLS clients fall back to Version 2.0 compatibility mode, they When TLS clients fall back to Version 2.0 compatibility mode, they
SHOULD use special PKCS #1 block formatting. This is done so that MUST use special PKCS#1 block formatting. This is done so that TLS
TLS servers will reject Version 2.0 sessions with TLS-capable servers will reject Version 2.0 sessions with TLS-capable clients.
clients.
When TLS clients are in Version 2.0 compatibility mode, they set the When a client negotiates SSL 2.0 but also supports TLS, it MUST set
right-hand (least significant) 8 random bytes of the PKCS padding the right-hand (least-significant) 8 random bytes of the PKCS padding
(not including the terminal null of the padding) for the RSA (not including the terminal null of the padding) for the RSA
encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY encryption of the ENCRYPTED-KEY-DATA field of the CLIENT-MASTER-KEY
to 0x03 (the other padding bytes are random). After decrypting the to 0x03 (the other padding bytes are random).
ENCRYPTED-KEY-DATA field, servers that support TLS SHOULD issue an
error if these eight padding bytes are 0x03. Version 2.0 servers When a TLS-capable server negotiates SSL 2.0 it SHOULD, after
receiving blocks padded in this manner will proceed normally. decrypting the ENCRYPTED-KEY-DATA field, check that these eight
padding bytes are 0x03. If they are not, the server SHOULD generate a
random value for SECRET-KEY-DATA, and continue the handshake (which
will eventually fail since the keys will not match). Note that
reporting the error situation to the client could make the server
vulnerable to attacks described in [BLEI].
Appendix F. Security Analysis Appendix F. Security Analysis
The TLS protocol is designed to establish a secure connection between The TLS protocol is designed to establish a secure connection between
a client and a server communicating over an insecure channel. This a client and a server communicating over an insecure channel. This
document makes several traditional assumptions, including that document makes several traditional assumptions, including that
attackers have substantial computational resources and cannot obtain attackers have substantial computational resources and cannot obtain
secret information from sources outside the protocol. Attackers are secret information from sources outside the protocol. Attackers are
assumed to have the ability to capture, modify, delete, replay, and assumed to have the ability to capture, modify, delete, replay, and
otherwise tamper with messages sent over the communication channel. otherwise tamper with messages sent over the communication channel.
This appendix outlines how TLS has been designed to resist a variety This appendix outlines how TLS has been designed to resist a variety
of attacks. of attacks.
F.1. Handshake Protocol F.1. Handshake Protocol
The handshake protocol is responsible for selecting a CipherSpec and The handshake protocol is responsible for selecting a CipherSpec and
generating a Master Secret, which together comprise the primary generating a Master Secret, which together comprise the primary
cryptographic parameters associated with a secure session. The cryptographic parameters associated with a secure session. The
handshake protocol can also optionally authenticate parties who have handshake protocol can also optionally authenticate parties who have
certificates signed by a trusted certificate authority. certificates signed by a trusted certificate authority.
F.1.1. Authentication and Key Exchange F.1.1. Authentication and Key Exchange
TLS supports three authentication modes: authentication of both TLS supports three authentication modes: authentication of both
parties, server authentication with an unauthenticated client, and parties, server authentication with an unauthenticated client, and
total anonymity. Whenever the server is authenticated, the channel total anonymity. Whenever the server is authenticated, the channel is
is secure against man-in-the-middle attacks, but completely anonymous secure against man-in-the-middle attacks, but completely anonymous
sessions are inherently vulnerable to such attacks. Anonymous sessions are inherently vulnerable to such attacks. Anonymous
servers cannot authenticate clients. If the server is authenticated, servers cannot authenticate clients. If the server is authenticated,
its certificate message must provide a valid certificate chain its certificate message must provide a valid certificate chain
leading to an acceptable certificate authority. Similarly, leading to an acceptable certificate authority. Similarly,
authenticated clients must supply an acceptable certificate to the authenticated clients must supply an acceptable certificate to the
server. Each party is responsible for verifying that the other's server. Each party is responsible for verifying that the other's
certificate is valid and has not expired or been revoked. certificate is valid and has not expired or been revoked.
The general goal of the key exchange process is to create a The general goal of the key exchange process is to create a
pre_master_secret known to the communicating parties and not to pre_master_secret known to the communicating parties and not to
attackers. The pre_master_secret will be used to generate the attackers. The pre_master_secret will be used to generate the
master_secret (see Section 8.1). The master_secret is required to master_secret (see Section 8.1). The master_secret is required to
generate the finished messages, encryption keys, and MAC secrets (see generate the finished messages, encryption keys, and MAC keys (see
Sections 7.4.8, 7.4.9, and 6.3). By sending a correct finished Sections 7.4.9 and 6.3). By sending a correct finished message,
message, parties thus prove that they know the correct parties thus prove that they know the correct pre_master_secret.
pre_master_secret.
F.1.1.1. Anonymous Key Exchange F.1.1.1. Anonymous Key Exchange
Completely anonymous sessions can be established using RSA or Diffie- Completely anonymous sessions can be established using Diffie-Hellman
Hellman for key exchange. With anonymous RSA, the client encrypts a for key exchange. The server's public parameters are contained in the
pre_master_secret with the server's uncertified public key extracted server key exchange message and the client's are sent in the client
from the server key exchange message. The result is sent in a client key exchange message. Eavesdroppers who do not know the private
key exchange message. Since eavesdroppers do not know the server's values should not be able to find the Diffie-Hellman result (i.e. the
private key, it will be infeasible for them to decode the pre_master_secret).
pre_master_secret.
Note: No anonymous RSA Cipher Suites are defined in this document.
With Diffie-Hellman, the server's public parameters are contained in
the server key exchange message and the client's are sent in the
client key exchange message. Eavesdroppers who do not know the
private values should not be able to find the Diffie-Hellman result
(i.e., the pre_master_secret).
Warning: Completely anonymous connections only provide protection Warning: Completely anonymous connections only provide protection
against passive eavesdropping. Unless an independent against passive eavesdropping. Unless an independent tamper-proof
tamper-proof channel is used to verify that the finished channel is used to verify that the finished messages were not
messages were not replaced by an attacker, server replaced by an attacker, server authentication is required in
authentication is required in environments where active environments where active man-in-the-middle attacks are a concern.
man-in-the-middle attacks are a concern.
F.1.1.2. RSA Key Exchange and Authentication F.1.1.2. RSA Key Exchange and Authentication
With RSA, key exchange and server authentication are combined. The With RSA, key exchange and server authentication are combined. The
public key either may be contained in the server's certificate or may public key is contained in the server's certificate. Note that
be a temporary RSA key sent in a server key exchange message. When compromise of the server's static RSA key results in a loss of
temporary RSA keys are used, they are signed by the server's RSA confidentiality for all sessions protected under that static key. TLS
certificate. The signature includes the current ClientHello.random, users desiring Perfect Forward Secrecy should use DHE cipher suites.
so old signatures and temporary keys cannot be replayed. Servers may The damage done by exposure of a private key can be limited by
use a single temporary RSA key for multiple negotiation sessions. changing one's private key (and certificate) frequently.
Note: The temporary RSA key option is useful if servers need large
certificates but must comply with government-imposed size
limits on keys used for key exchange.
Note that if ephemeral RSA is not used, compromise of the server's
static RSA key results in a loss of confidentiality for all sessions
protected under that static key. TLS users desiring Perfect Forward
Secrecy should use DHE cipher suites. The damage done by exposure of
a private key can be limited by changing one's private key (and
certificate) frequently.
After verifying the server's certificate, the client encrypts a After verifying the server's certificate, the client encrypts a
pre_master_secret with the server's public key. By successfully pre_master_secret with the server's public key. By successfully
decoding the pre_master_secret and producing a correct finished decoding the pre_master_secret and producing a correct finished
message, the server demonstrates that it knows the private key message, the server demonstrates that it knows the private key
corresponding to the server certificate. corresponding to the server certificate.
When RSA is used for key exchange, clients are authenticated using When RSA is used for key exchange, clients are authenticated using
the certificate verify message (see Section 7.4.8). The client signs the certificate verify message (see Section 7.4.8). The client signs
a value derived from the master_secret and all preceding handshake a value derived from all preceding handshake messages. These
messages. These handshake messages include the server certificate, handshake messages include the server certificate, which binds the
which binds the signature to the server, and ServerHello.random, signature to the server, and ServerHello.random, which binds the
which binds the signature to the current handshake process. signature to the current handshake process.
F.1.1.3. Diffie-Hellman Key Exchange with Authentication F.1.1.3. Diffie-Hellman Key Exchange with Authentication
When Diffie-Hellman key exchange is used, the server can either When Diffie-Hellman key exchange is used, the server can either
supply a certificate containing fixed Diffie-Hellman parameters or supply a certificate containing fixed Diffie-Hellman parameters or
use the server key exchange message to send a set of temporary use the server key exchange message to send a set of temporary
Diffie-Hellman parameters signed with a DSS or RSA certificate. Diffie-Hellman parameters signed with a DSS or RSA certificate.
Temporary parameters are hashed with the hello.random values before Temporary parameters are hashed with the hello.random values before
signing to ensure that attackers do not replay old parameters. In signing to ensure that attackers do not replay old parameters. In
either case, the client can verify the certificate or signature to either case, the client can verify the certificate or signature to
ensure that the parameters belong to the server. ensure that the parameters belong to the server.
If the client has a certificate containing fixed Diffie-Hellman If the client has a certificate containing fixed Diffie-Hellman
parameters, its certificate contains the information required to parameters, its certificate contains the information required to
complete the key exchange. Note that in this case the client and complete the key exchange. Note that in this case the client and
server will generate the same Diffie-Hellman result (i.e., server will generate the same Diffie-Hellman result (i.e.,
pre_master_secret) every time they communicate. To prevent the pre_master_secret) every time they communicate. To prevent the
pre_master_secret from staying in memory any longer than necessary, pre_master_secret from staying in memory any longer than necessary,
it should be converted into the master_secret as soon as possible. it should be converted into the master_secret as soon as possible.
Client Diffie-Hellman parameters must be compatible with those Client Diffie-Hellman parameters must be compatible with those
supplied by the server for the key exchange to work. supplied by the server for the key exchange to work.
If the client has a standard DSS or RSA certificate or is If the client has a standard DSS or RSA certificate or is
unauthenticated, it sends a set of temporary parameters to the server unauthenticated, it sends a set of temporary parameters to the server
in the client key exchange message, then optionally uses a in the client key exchange message, then optionally uses a
certificate verify message to authenticate itself. certificate verify message to authenticate itself.
If the same DH keypair is to be used for multiple handshakes, either If the same DH keypair is to be used for multiple handshakes, either
because the client or server has a certificate containing a fixed DH because the client or server has a certificate containing a fixed DH
keypair or because the server is reusing DH keys, care must be taken keypair or because the server is reusing DH keys, care must be taken
to prevent small subgroup attacks. Implementations SHOULD follow the to prevent small subgroup attacks. Implementations SHOULD follow the
guidelines found in [SUBGROUP]. guidelines found in [SUBGROUP].
Small subgroup attacks are most easily avoided by using one of the Small subgroup attacks are most easily avoided by using one of the
DHE ciphersuites and generating a fresh DH private key (X) for each DHE cipher suites and generating a fresh DH private key (X) for each
handshake. If a suitable base (such as 2) is chosen, g^X mod p can handshake. If a suitable base (such as 2) is chosen, g^X mod p can be
be computed very quickly, therefore the performance cost is computed very quickly, therefore the performance cost is minimized.
minimized. Additionally, using a fresh key for each handshake Additionally, using a fresh key for each handshake provides Perfect
provides Perfect Forward Secrecy. Implementations SHOULD generate a Forward Secrecy. Implementations SHOULD generate a new X for each
new X for each handshake when using DHE ciphersuites. handshake when using DHE cipher suites.
Because TLS allows the server to provide arbitrary DH groups, the
client should verify that the DH group is of suitable size as defined
by local policy. The client SHOULD also verify that the DH public
exponent appears to be of adequate size. [KEYSIZ] provides a useful
guide to the strength of various group sizes. The server MAY choose
to assist the client by providing a known group, such as those
defined in [IKEALG] or [MODP]. These can be verified by simple
comparison.
F.1.2. Version Rollback Attacks F.1.2. Version Rollback Attacks
Because TLS includes substantial improvements over SSL Version 2.0, Because TLS includes substantial improvements over SSL Version 2.0,
attackers may try to make TLS-capable clients and servers fall back attackers may try to make TLS-capable clients and servers fall back
to Version 2.0. This attack can occur if (and only if) two TLS- to Version 2.0. This attack can occur if (and only if) two TLS-
capable parties use an SSL 2.0 handshake. capable parties use an SSL 2.0 handshake.
Although the solution using non-random PKCS #1 block type 2 message Although the solution using non-random PKCS #1 block type 2 message
padding is inelegant, it provides a reasonably secure way for Version padding is inelegant, it provides a reasonably secure way for Version
3.0 servers to detect the attack. This solution is not secure 3.0 servers to detect the attack. This solution is not secure against
against attackers who can brute force the key and substitute a new attackers who can brute force the key and substitute a new ENCRYPTED-
ENCRYPTED-KEY-DATA message containing the same key (but with normal KEY-DATA message containing the same key (but with normal padding)
padding) before the application specified wait threshold has expired. before the application specified wait threshold has expired. Altering
Parties concerned about attacks of this scale should not use 40-bit the padding of the least significant 8 bytes of the PKCS padding does
encryption keys. Altering the padding of the least-significant 8 not impact security for the size of the signed hashes and RSA key
bytes of the PKCS padding does not impact security for the size of lengths used in the protocol, since this is essentially equivalent to
the signed hashes and RSA key lengths used in the protocol, since increasing the input block size by 8 bytes.
this is essentially equivalent to increasing the input block size by
8 bytes.
F.1.3. Detecting Attacks against the Handshake Protocol F.1.3. Detecting Attacks Against the Handshake Protocol
An attacker might try to influence the handshake exchange to make the An attacker might try to influence the handshake exchange to make the
parties select different encryption algorithms than they would parties select different encryption algorithms than they would
normally chooses. normally chooses.
For this attack, an attacker must actively change one or more For this attack, an attacker must actively change one or more
handshake messages. If this occurs, the client and server will handshake messages. If this occurs, the client and server will
compute different values for the handshake message hashes. As a compute different values for the handshake message hashes. As a
result, the parties will not accept each others' finished messages. result, the parties will not accept each others' finished messages.
Without the master_secret, the attacker cannot repair the finished Without the master_secret, the attacker cannot repair the finished
messages, so the attack will be discovered. messages, so the attack will be discovered.
F.1.4. Resuming Sessions F.1.4. Resuming Sessions
When a connection is established by resuming a session, new When a connection is established by resuming a session, new
ClientHello.random and ServerHello.random values are hashed with the ClientHello.random and ServerHello.random values are hashed with the
session's master_secret. Provided that the master_secret has not session's master_secret. Provided that the master_secret has not been
been compromised and that the secure hash operations used to produce compromised and that the secure hash operations used to produce the
the encryption keys and MAC secrets are secure, the connection should encryption keys and MAC keys are secure, the connection should be
be secure and effectively independent from previous connections. secure and effectively independent from previous connections.
Attackers cannot use known encryption keys or MAC secrets to Attackers cannot use known encryption keys or MAC secrets to
compromise the master_secret without breaking the secure hash compromise the master_secret without breaking the secure hash
operations (which use both SHA and MD5). operations.
Sessions cannot be resumed unless both the client and server agree. Sessions cannot be resumed unless both the client and server agree.
If either party suspects that the session may have been compromised, If either party suspects that the session may have been compromised,
or that certificates may have expired or been revoked, it should or that certificates may have expired or been revoked, it should
force a full handshake. An upper limit of 24 hours is suggested for force a full handshake. An upper limit of 24 hours is suggested for
session ID lifetimes, since an attacker who obtains a master_secret session ID lifetimes, since an attacker who obtains a master_secret
may be able to impersonate the compromised party until the may be able to impersonate the compromised party until the
corresponding session ID is retired. Applications that may be run in corresponding session ID is retired. Applications that may be run in
relatively insecure environments should not write session IDs to relatively insecure environments should not write session IDs to
stable storage. stable storage.
F.1.5. MD5 and SHA
TLS uses hash functions very conservatively. Where possible, both
MD5 and SHA are used in tandem to ensure that non-catastrophic flaws
in one algorithm will not break the overall protocol.
F.2. Protecting Application Data F.2. Protecting Application Data
The master_secret is hashed with the ClientHello.random and The master_secret is hashed with the ClientHello.random and
ServerHello.random to produce unique data encryption keys and MAC ServerHello.random to produce unique data encryption keys and MAC
secrets for each connection. secrets for each connection.
Outgoing data is protected with a MAC before transmission. To Outgoing data is protected with a MAC before transmission. To prevent
prevent message replay or modification attacks, the MAC is computed message replay or modification attacks, the MAC is computed from the
from the MAC secret, the sequence number, the message length, the MAC key, the sequence number, the message length, the message
message contents, and two fixed character strings. The message type contents, and two fixed character strings. The message type field is
field is necessary to ensure that messages intended for one TLS necessary to ensure that messages intended for one TLS Record Layer
Record Layer client are not redirected to another. The sequence client are not redirected to another. The sequence number ensures
number ensures that attempts to delete or reorder messages will be that attempts to delete or reorder messages will be detected. Since
detected. Since sequence numbers are 64 bits long, they should never sequence numbers are 64 bits long, they should never overflow.
overflow. Messages from one party cannot be inserted into the Messages from one party cannot be inserted into the other's output,
other's output, since they use independent MAC secrets. Similarly, since they use independent MAC keys. Similarly, the server-write and
the server-write and client-write keys are independent, so stream client-write keys are independent, so stream cipher keys are used
cipher keys are used only once. only once.
If an attacker does break an encryption key, all messages encrypted If an attacker does break an encryption key, all messages encrypted
with it can be read. Similarly, compromise of a MAC key can make with it can be read. Similarly, compromise of a MAC key can make
message modification attacks possible. Because MACs are also message modification attacks possible. Because MACs are also
encrypted, message-alteration attacks generally require breaking the encrypted, message-alteration attacks generally require breaking the
encryption algorithm as well as the MAC. encryption algorithm as well as the MAC.
Note: MAC secrets may be larger than encryption keys, so messages can Note: MAC keys may be larger than encryption keys, so messages can
remain tamper resistant even if encryption keys are broken. remain tamper resistant even if encryption keys are broken.
F.3. Explicit IVs F.3. Explicit IVs
[CBCATT] describes a chosen plaintext attack on TLS that depends on [CBCATT] describes a chosen plaintext attack on TLS that depends on
knowing the IV for a record. Previous versions of TLS [TLS1.0] used knowing the IV for a record. Previous versions of TLS [TLS1.0] used
the CBC residue of the previous record as the IV and therefore the CBC residue of the previous record as the IV and therefore
enabled this attack. This version uses an explicit IV in order to enabled this attack. This version uses an explicit IV in order to
protect against this attack. protect against this attack.
F.4. Security of Composite Cipher Modes F.4. Security of Composite Cipher Modes
TLS secures transmitted application data via the use of symmetric TLS secures transmitted application data via the use of symmetric
encryption and authentication functions defined in the negotiated encryption and authentication functions defined in the negotiated
ciphersuite. The objective is to protect both the integrity and cipher suite. The objective is to protect both the integrity and
confidentiality of the transmitted data from malicious actions by confidentiality of the transmitted data from malicious actions by
active attackers in the network. It turns out that the order in active attackers in the network. It turns out that the order in
which encryption and authentication functions are applied to the data which encryption and authentication functions are applied to the data
plays an important role for achieving this goal [ENCAUTH]. plays an important role for achieving this goal [ENCAUTH].
The most robust method, called encrypt-then-authenticate, first The most robust method, called encrypt-then-authenticate, first
applies encryption to the data and then applies a MAC to the applies encryption to the data and then applies a MAC to the
ciphertext. This method ensures that the integrity and ciphertext. This method ensures that the integrity and
confidentiality goals are obtained with ANY pair of encryption and confidentiality goals are obtained with ANY pair of encryption and
MAC functions, provided that the former is secure against chosen MAC functions, provided that the former is secure against chosen
plaintext attacks and that the MAC is secure against chosen-message plaintext attacks and that the MAC is secure against chosen-message
attacks. TLS uses another method, called authenticate-then-encrypt, attacks. TLS uses another method, called authenticate-then-encrypt,
in which first a MAC is computed on the plaintext and then the in which first a MAC is computed on the plaintext and then the
concatenation of plaintext and MAC is encrypted. This method has concatenation of plaintext and MAC is encrypted. This method has
been proven secure for CERTAIN combinations of encryption functions been proven secure for CERTAIN combinations of encryption functions
and MAC functions, but it is not guaranteed to be secure in general. and MAC functions, but it is not guaranteed to be secure in general.
In particular, it has been shown that there exist perfectly secure In particular, it has been shown that there exist perfectly secure
encryption functions (secure even in the information-theoretic sense) encryption functions (secure even in the information-theoretic sense)
that combined with any secure MAC function, fail to provide the that combined with any secure MAC function, fail to provide the
confidentiality goal against an active attack. Therefore, new confidentiality goal against an active attack. Therefore, new cipher
ciphersuites and operation modes adopted into TLS need to be analyzed suites and operation modes adopted into TLS need to be analyzed under
under the authenticate-then-encrypt method to verify that they the authenticate-then-encrypt method to verify that they achieve the
achieve the stated integrity and confidentiality goals. stated integrity and confidentiality goals.
Currently, the security of the authenticate-then-encrypt method has Currently, the security of the authenticate-then-encrypt method has
been proven for some important cases. One is the case of stream been proven for some important cases. One is the case of stream
ciphers in which a computationally unpredictable pad of the length of ciphers in which a computationally unpredictable pad of the length of
the message, plus the length of the MAC tag, is produced using a the message, plus the length of the MAC tag, is produced using a
pseudo-random generator and this pad is xor-ed with the concatenation pseudo-random generator and this pad is xor-ed with the concatenation
of plaintext and MAC tag. The other is the case of CBC mode using a of plaintext and MAC tag. The other is the case of CBC mode using a
secure block cipher. In this case, security can be shown if one secure block cipher. In this case, security can be shown if one
applies one CBC encryption pass to the concatenation of plaintext and applies one CBC encryption pass to the concatenation of plaintext and
MAC and uses a new, independent, and unpredictable IV for each new MAC and uses a new, independent, and unpredictable IV for each new
pair of plaintext and MAC. In previous versions of SSL, CBC mode was pair of plaintext and MAC. In versions of TLS prior to 1.1, CBC mode
used properly EXCEPT that it used a predictable IV in the form of the was used properly EXCEPT that it used a predictable IV in the form of
last block of the previous ciphertext. This made TLS open to chosen the last block of the previous ciphertext. This made TLS open to
plaintext attacks. This version of the protocol is immune to those chosen plaintext attacks. This version of the protocol is immune to
attacks. For exact details in the encryption modes proven secure, those attacks. For exact details in the encryption modes proven
see [ENCAUTH]. secure, see [ENCAUTH].
F.5. Denial of Service F.5 Denial of Service
TLS is susceptible to a number of denial of service (DoS) attacks. TLS is susceptible to a number of denial of service (DoS) attacks.
In particular, an attacker who initiates a large number of TCP In particular, an attacker who initiates a large number of TCP
connections can cause a server to consume large amounts of CPU doing connections can cause a server to consume large amounts of CPU doing
RSA decryption. However, because TLS is generally used over TCP, it RSA decryption. However, because TLS is generally used over TCP, it
is difficult for the attacker to hide his point of origin if proper is difficult for the attacker to hide his point of origin if proper
TCP SYN randomization is used [SEQNUM] by the TCP stack. TCP SYN randomization is used [SEQNUM] by the TCP stack.
Because TLS runs over TCP, it is also susceptible to a number of Because TLS runs over TCP, it is also susceptible to a number of
denial of service attacks on individual connections. In particular, denial of service attacks on individual connections. In particular,
attackers can forge RSTs, thereby terminating connections, or forge attackers can forge RSTs, thereby terminating connections, or forge
partial TLS records, thereby causing the connection to stall. These partial TLS records, thereby causing the connection to stall. These
attacks cannot in general be defended against by a TCP-using attacks cannot in general be defended against by a TCP-using
protocol. Implementors or users who are concerned with this class of protocol. Implementors or users who are concerned with this class of
attack should use IPsec AH [AH-ESP] or ESP [AH-ESP]. attack should use IPsec AH [AH] or ESP [ESP].
F.6. Final Notes F.6 Final Notes
For TLS to be able to provide a secure connection, both the client For TLS to be able to provide a secure connection, both the client
and server systems, keys, and applications must be secure. In and server systems, keys, and applications must be secure. In
addition, the implementation must be free of security errors. addition, the implementation must be free of security errors.
The system is only as strong as the weakest key exchange and The system is only as strong as the weakest key exchange and
authentication algorithm supported, and only trustworthy authentication algorithm supported, and only trustworthy
cryptographic functions should be used. Short public keys, 40-bit cryptographic functions should be used. Short public keys and
bulk encryption keys, and anonymous servers should be used with great anonymous servers should be used with great caution. Implementations
caution. Implementations and users must be careful when deciding and users must be careful when deciding which certificates and
which certificates and certificate authorities are acceptable; a certificate authorities are acceptable; a dishonest certificate
dishonest certificate authority can do tremendous damage. authority can do tremendous damage.
Normative References Changes in This Version
[RFC Editor: Please delete this]
[AES] National Institute of Standards and Technology, - Added a new pitfall about fragmenting messages when necessary
"Specification for the Advanced Encryption Standard (AES)" [Issue #71]
FIPS 197. November 26, 2001.
[3DES] W. Tuchman, "Hellman Presents No Shortcut Solutions To - Added Updates: RFC 4492 [Issue #83]
DES," IEEE Spectrum, v. 16, n. 7, July 1979, pp. 40-41.
[DES] ANSI X3.106, "American National Standard for Information - Long CBC padding pitfall [Issue #73]
Systems-Data Link Encryption," American National Standards
Institute, 1983.
[DSS] NIST FIPS PUB 186-2, "Digital Signature Standard," - Fixed ProtocolVersion structure [Issue #79]
National Institute of Standards and Technology, U.S.
Department of Commerce, 2000.
[HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- - Cleaned up extensions text [Issue #78]
Hashing for Message Authentication", RFC 2104, February
1997.
[IDEA] X. Lai, "On the Design and Security of Block Ciphers," ETH - Clarified alerts some [Issue #85]
Series in Information Processing, v. 1, Konstanz:
Hartung-Gorre Verlag, 1992.
[MD5] Rivest, R., "The MD5 Message-Digest Algorithm ", RFC 1321, - Added AES to the table in Appendix C [Issue #72]
April 1992.
[PKCS1A] B. Kaliski, "Public-Key Cryptography Standards (PKCS) #1: - Tightened up when signature_algorithms is used
RSA Cryptography Specifications Version 1.5", RFC 2313, (it is now a MUST if you support other than SHA-1)
March 1998. and the interpretation when it is absent is also a MUST
[Issue #67]
[PKCS1B] J. Jonsson, B. Kaliski, "Public-Key Cryptography Standards - Cleaned up "cipher suite" so it's always two words outside
(PKCS) #1: RSA Cryptography Specifications Version 2.1", of when it refers to the syntactic type [Issue #68]
RFC 3447, February 2003.
[PKIX] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet - Misc editorial.
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[RC2] Rivest, R., "A Description of the RC2(r) Encryption - Added support for SHA256 cipher suites
Algorithm", RFC 2268, March 1998.
[SCH] B. Schneier. "Applied Cryptography: Protocols, Algorithms, - Clarified warning alert behavior and client certificate omission
and Source Code in C, 2ed", Published by John Wiley & behavior [Issue #84]
Sons, Inc. 1996.
[SHA] NIST FIPS PUB 180-2, "Secure Hash Standard," National - Removed IDEA and DES entirely for documentation in a separate doc
Institute of Standards and Technology, U.S. Department of [Issue #64]
Commerce., August 2001.
[REQ] Bradner, S., "Key words for use in RFCs to Indicate - Changed the presentation language to allow fall-through to simplify
Requirement Levels", BCP 14, RFC 2119, March 1997. some of the PDUs.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an - Cleaned up KeyExchangeAlgorithm ClientKeyExchange to use values
IANA Considerations Section in RFCs", BCP 26, RFC 2434, that match Appendix C.
October 1998.
[TLSAES] Chown, P., "Advanced Encryption Standard (AES) - Changed digitally-signed to include SignatureAndHashAlgorithm
Ciphersuites for Transport Layer Security (TLS)", RFC (another simplification)
3268, June 2002.
[TLSEXT] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., - Considerations for RFC 4492
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 3546, June 2003.
[TLSKRB] Medvinsky, A. and M. Hur, "Addition of Kerberos Cipher Normative References
Suites to Transport Layer Security (TLS)", RFC 2712,
October 1999. [AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard (AES)"
FIPS 197. November 26, 2001.
[3DES] National Institute of Standards and Technology,
"Recommendation for the Triple Data Encryption Algorithm
(TDEA) Block Cipher", NIST Special Publication 800-67, May
2004.
[DES] National Institute of Standards and Technology, "Data
Encryption Standard (DES)", FIPS PUB 46-3, October 1999.
[DSS] NIST FIPS PUB 186-2, "Digital Signature Standard," National
Institute of Standards and Technology, U.S. Department of
Commerce, 2000.
[HMAC] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.
[MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321,
April 1992.
[PKCS1] J. Jonsson, B. Kaliski, "Public-Key Cryptography Standards
(PKCS) #1: RSA Cryptography Specifications Version 2.1", RFC
3447, February 2003.
[PKIX] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet X.509
Public Key Infrastructure Certificate and Certificate
Revocation List (CRL) Profile", RFC 3280, April 2002.
[SCH] B. Schneier. "Applied Cryptography: Protocols, Algorithms,
and Source Code in C, 2nd ed.", Published by John Wiley &
Sons, Inc. 1996.
[SHA] NIST FIPS PUB 180-2, "Secure Hash Standard," National
Institute of Standards and Technology, U.S. Department of
Commerce., August 2001.
[REQ] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 25, RFC 2434,
October 1998.
Informative References Informative References
[AH-ESP] Kent, S., "IP Authentication Header", RFC 4302, December [AEAD] Mcgrew, D., "Authenticated Encryption", July 2007, draft-
2005. mcgrew-auth-enc-05.txt.
Eastlake 3rd, D., "Cryptographic Algorithm Implementation [AH] Kent, S., and Atkinson, R., "IP Authentication Header", RFC
Requirements for Encapsulating Security Payload (ESP) and 4302, December 2005.
Authentication Header (AH)", RFC 4305, December 2005.
[BLEI] Bleichenbacher D., "Chosen Ciphertext Attacks against [BLEI] Bleichenbacher D., "Chosen Ciphertext Attacks against
Protocols Based on RSA Encryption Standard PKCS #1" in Protocols Based on RSA Encryption Standard PKCS #1" in
Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462, Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462, pages:
pages: 1-12, 1998. 1-12, 1998.
[CBCATT] Moeller, B., "Security of CBC Ciphersuites in SSL/TLS: [CBCATT] Moeller, B., "Security of CBC Ciphersuites in SSL/TLS:
Problems and Countermeasures", Problems and Countermeasures",
http://www.openssl.org/~bodo/tls-cbc.txt. http://www.openssl.org/~bodo/tls-cbc.txt.
[CBCTIME] Canvel, B., "Password Interception in a SSL/TLS Channel", [CBCTIME] Canvel, B., Hiltgen, A., Vaudenay, S., and M. Vuagnoux,
http://lasecwww.epfl.ch/memo_ssl.shtml, 2003. "Password Interception in a SSL/TLS Channel", Advances in
Cryptology -- CRYPTO 2003, LNCS vol. 2729, 2003.
[ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication [CCM] "NIST Special Publication 800-38C: The CCM Mode for
for Protecting Communications (Or: How Secure is SSL?)", Authentication and Confidentiality",
Crypto 2001. http://csrc.nist.gov/publications/nistpubs/800-38C/
SP800-38C.pdf
[KPR03] Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based [DSS-3] NIST FIPS PUB 186-3 Draft, "Digital Signature Standard,"
Sessions in SSL/TLS", http://eprint.iacr.org/2003/052/, National Institute of Standards and Technology, U.S.
March 2003. Department of Commerce, 2006.
[PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate [ENCAUTH] Krawczyk, H., "The Order of Encryption and Authentication
Syntax Standard," version 1.5, November 1993. for Protecting Communications (Or: How Secure is SSL?)",
Crypto 2001.
[PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message [ESP] Kent, S., and Atkinson, R., "IP Encapsulating Security
Syntax Standard," version 1.5, November 1993. Payload (ESP)", RFC 4303, December 2005.
[RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker, [FI06] Hal Finney, "Bleichenbacher's RSA signature forgery based on
"Randomness Requirements for Security", BCP 106, RFC 4086, implementation error", ietf-openpgp@imc.org mailing list, 27
June 2005. August 2006, http://www.imc.org/ietf-openpgp/mail-
archive/msg14307.html.
[RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for [GCM] "NIST Special Publication 800-38D DRAFT (June, 2007):
Obtaining Digital Signatures and Public-Key Recommendation for Block Cipher Modes of Operation:
Cryptosystems," Communications of the ACM, v. 21, n. 2, Galois/Counter Mode (GCM) and GMAC"
Feb 1978, pp. 120-126.
[SEQNUM] Bellovin, S., "Defending Against Sequence Number Attacks", [IKEALG] Schiller, J., "Cryptographic Algorithms for Use in the
RFC 1948, May 1996. Internet Key Exchange Version 2 (IKEv2)", RFC 4307, December
2005.
[SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications [KEYSIZ] Orman, H., and Hoffman, P., "Determining Strengths For
Corp., Feb 9, 1995. Public Keys Used For Exchanging Symmetric Keys" RFC 3766,
April 2004.
[SSL3] A. Frier, P. Karlton, and P. Kocher, "The SSL 3.0 [KPR03] Klima, V., Pokorny, O., Rosa, T., "Attacking RSA-based
Protocol", Netscape Communications Corp., Nov 18, 1996. Sessions in SSL/TLS", http://eprint.iacr.org/2003/052/,
March 2003.
[SUBGROUP] Zuccherato, R., "Methods for Avoiding the "Small-Subgroup" [MODP] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Attacks on the Diffie-Hellman Key Agreement Method for Diffie-Hellman groups for Internet Key Exchange (IKE)", RFC
S/MIME", RFC 2785, March 2000. 3526, May 2003.
[TCP] Hellstrom, G. and P. Jones, "RTP Payload for Text [PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate Syntax
Conversation", RFC 4103, June 2005. Standard," version 1.5, November 1993.
[TIMING] Boneh, D., Brumley, D., "Remote timing attacks are [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message Syntax
practical", USENIX Security Symposium 2003. Standard," version 1.5, November 1993.
[TLS1.0] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", [RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker, "Randomness
RFC 2246, January 1999. Requirements for Security", BCP 106, RFC 4086, June 2005.
[X501] ITU-T Recommendation X.501: Information Technology - Open [RFC3749] Hollenbeck, S., "Transport Layer Security Protocol
Systems Interconnection - The Directory: Models, 1993. Compression Methods", RFC 3749, May 2004.
[X509] ITU-T Recommendation X.509 (1997 E): Information [RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
Technology - Open Systems Interconnection - "The Directory Wright, T., "Transport Layer Security (TLS) Extensions", RFC
- Authentication Framework". 1988. 4366, April 2006.
[XDR] Srinivasan, R., "XDR: External Data Representation [RSA] R. Rivest, A. Shamir, and L. M. Adleman, "A Method for
Standard", RFC 1832, August 1995. Obtaining Digital Signatures and Public-Key Cryptosystems,"
Communications of the ACM, v. 21, n. 2, Feb 1978, pp.
120-126.
Authors' Addresses [SEQNUM] Bellovin. S., "Defending Against Sequence Number Attacks",
RFC 1948, May 1996.
Working Group Chairs [SSL2] Hickman, Kipp, "The SSL Protocol", Netscape Communications
Corp., Feb 9, 1995.
Win Treese [SSL3] A. Freier, P. Karlton, and P. Kocher, "The SSL 3.0
Protocol", Netscape Communications Corp., Nov 18, 1996.
EMail: treese@acm.org [SUBGROUP] Zuccherato, R., "Methods for Avoiding the "Small-Subgroup"
Attacks on the Diffie-Hellman Key Agreement Method for
S/MIME", RFC 2785, March 2000.
Eric Rescorla [TCP] Postel, J., "Transmission Control Protocol," STD 7, RFC 793,
September 1981.
EMail: ekr@rtfm.com [TIMING] Boneh, D., Brumley, D., "Remote timing attacks are
practical", USENIX Security Symposium 2003.
Editors [TLSAES] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites
for Transport Layer Security (TLS)", RFC 3268, June 2002.
Tim Dierks [TLSECC] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and
Independent Moeller, B., "Elliptic Curve Cryptography (ECC) Cipher
Suites for Transport Layer Security (TLS)", RFC 4492, May
2006.
EMail: tim@dierks.org [TLSEXT] Eastlake, D.E., "Transport Layer Security (TLS) Extensions:
Extension Definitions", January 2008, draft-ietf-tls-
rfc4366-bis-01.txt.
[TLSPGP] Mavrogiannopoulos, N., "Using OpenPGP keys for TLS
authentication", RFC 5081, November 2007.
[TLSPSK] Eronen, P., Tschofenig, H., "Pre-Shared Key Ciphersuites for
Transport Layer Security (TLS)", RFC 4279, December 2005.
[TLS1.0] Dierks, T., and C. Allen, "The TLS Protocol, Version 1.0",
RFC 2246, January 1999.
[TLS1.1] Dierks, T., and E. Rescorla, "The TLS Protocol, Version
1.1", RFC 4346, April, 2006.
[X501] ITU-T Recommendation X.501: Information Technology - Open
Systems Interconnection - The Directory: Models, 1993.
[XDR] Eisler, M., "External Data Representation Standard", RFC
4506, May 2006.
Credits
Working Group Chairs
Eric Rescorla Eric Rescorla
RTFM, Inc. EMail: ekr@networkresonance.com
EMail: ekr@rtfm.com Pasi Eronen
pasi.eronen@nokia.com
Other Contributors Editors
Tim Dierks Eric Rescorla
Independent Network Resonance, Inc.
EMail: tim@dierks.org EMail: ekr@networkresonance.com
Other contributors
Christopher Allen (co-editor of TLS 1.0) Christopher Allen (co-editor of TLS 1.0)
Alacrity Ventures Alacrity Ventures
EMail: ChristopherA@AlacrityManagement.com ChristopherA@AlacrityManagement.com
Martin Abadi Martin Abadi
University of California, Santa Cruz University of California, Santa Cruz
EMail: abadi@cs.ucsc.edu abadi@cs.ucsc.edu
Steven M. Bellovin
Columbia University
smb@cs.columbia.edu
Simon Blake-Wilson
BCI
EMail: sblakewilson@bcisse.com
Ran Canetti Ran Canetti
IBM IBM
EMail: canetti@watson.ibm.com canetti@watson.ibm.com
Pete Chown
Skygate Technology Ltd
pc@skygate.co.uk
Taher Elgamal Taher Elgamal
taher@securify.com
Securify Securify
EMail: taher@securify.com
Pasi Eronen
pasi.eronen@nokia.com
Nokia
Anil Gangolli Anil Gangolli
EMail: anil@busybuddha.org anil@busybuddha.org
Kipp Hickman Kipp Hickman
Alfred Hoenes
David Hopwood
Independent Consultant
EMail: david.hopwood@blueyonder.co.uk
Phil Karlton (co-author of SSLv3) Phil Karlton (co-author of SSLv3)
Paul Kocher (co-author of SSLv3) Paul Kocher (co-author of SSLv3)
Cryptography Research Cryptography Research
EMail: paul@cryptography.com paul@cryptography.com
Hugo Krawczyk Hugo Krawczyk
Technion Israel Institute of Technology IBM
EMail: hugo@ee.technion.ac.il hugo@ee.technion.ac.il
Jan Mikkelsen
Transactionware
EMail: janm@transactionware.com
Magnus Nystrom
RSA Security
EMail: magnus@rsasecurity.com
Robert Relyea Robert Relyea
Netscape Communications Netscape Communications
EMail: relyea@netscape.com relyea@netscape.com
Jim Roskind Jim Roskind
Netscape Communications Netscape Communications
EMail: jar@netscape.com jar@netscape.com
Michael Sabin Michael Sabin
Dan Simon Dan Simon
Microsoft, Inc. Microsoft, Inc.
EMail: dansimon@microsoft.com dansimon@microsoft.com
Tom Weinstein Tom Weinstein
Tim Wright
Vodafone
EMail: timothy.wright@vodafone.com
Comments Comments
The discussion list for the IETF TLS working group is located at the The discussion list for the IETF TLS working group is located at the
e-mail address <ietf-tls@lists.consensus.com>. Information on the e-mail address <tls@ietf.org>. Information on the group and
group and information on how to subscribe to the list is at information on how to subscribe to the list is at
<http://lists.consensus.com/>. <https://www1.ietf.org/mailman/listinfo/tls>
Archives of the list can be found at: Archives of the list can be found at:
<http://www.imc.org/ietf-tls/mail-archive/> <http://www.ietf.org/mail-archive/web/tls/current/index.html>
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2006). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
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such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
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http://www.ietf.org/ipr. http://www.ietf.org/ipr.
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Acknowledgement Acknowledgment
Funding for the RFC Editor function is provided by the IETF Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA). Administrative Support Activity (IASA).
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