draft-ietf-tls-cached-info-08.txt   draft-ietf-tls-cached-info-09.txt 
INTERNET-DRAFT S. Santesson (3xA Security) INTERNET-DRAFT S. Santesson (3xA Security)
Intended Status: Proposed Standard Intended Status: Proposed Standard
Expires: October 22, 2010 April 20, 2010 Expires: January 13, 2011 July 12, 2010
Transport Layer Security (TLS) Cached Information Extension Transport Layer Security (TLS) Cached Information Extension
<draft-ietf-tls-cached-info-08.txt> <draft-ietf-tls-cached-info-09.txt>
Abstract Abstract
This document defines a Transport Layer Security (TLS) extension for This document defines a Transport Layer Security (TLS) extension for
cached information. This extension allows the TLS client to inform a cached information. This extension allows the TLS client to inform a
server of cached information from previous TLS sessions, allowing the server of cached information from previous TLS handshakes, allowing
server to omit sending cached static information to the client during the server to omit sending cached static information to the client
the TLS handshake protocol exchange. during the TLS handshake protocol exchange.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as other groups may also distribute working documents as
Internet-Drafts. Internet-Drafts.
skipping to change at page 2, line 26 skipping to change at page 2, line 26
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Cached Information Extension . . . . . . . . . . . . . . . . . 4 2. Cached Information Extension . . . . . . . . . . . . . . . . . 4
3. Extension Exchange . . . . . . . . . . . . . . . . . . . . . . 5 3. Extension Exchange . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Reconnaissance . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Cached Information . . . . . . . . . . . . . . . . . . . . 5
3.2. Cached Information . . . . . . . . . . . . . . . . . . . . 5 3.2. Reconnaissance . . . . . . . . . . . . . . . . . . . . . . 5
4. Data Substitution . . . . . . . . . . . . . . . . . . . . . . . 6 4. Cached Information Substitution . . . . . . . . . . . . . . . . 6
4.1. Data Substitution Syntax for certificate_chain . . . . . . 6 4.1. Substitution Syntax for certificate_chain . . . . . . . . 6
4.2. Data Substitution Syntax for trusted_cas . . . . . . . . . 7 4.2. Substitution Syntax for trusted_cas . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . . 9 8. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Annex A - 64 bit FNV-1a digest . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
A.1. Definition (Normative) . . . . . . . . . . . . . . . . . 10
A.2 Java code sample (Informative) . . . . . . . . . . . . . 11
A.3. C code sample (Informative) . . . . . . . . . . . . . . . 12
A.4. Digest samples (Informative) . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
TLS handshakes often include fairly static information such as server TLS handshakes often include fairly static information such as server
certificate and a list of trusted Certification Authorities (CAs). certificate and a list of trusted Certification Authorities (CAs).
Static information such as a server certificate can be of Static information such as a server certificate can be of
considerable size. This is the case in particular if the server considerable size. This is the case in particular if the server
certificate is bundled with a complete certificate path, including certificate is bundled with a complete certificate path, including
all intermediary certificates up to the trust anchor public key. all intermediary certificates up to the trust anchor public key.
Significant benefits can be achieved in low bandwidth and high Significant benefits can be achieved in low bandwidth and high
latency networks, in particular if the communication channel also has latency networks, in particular if the communication channel also has
a relatively high rate of transmission errors, if a known and a relatively high rate of transmission errors, if a known and
previously cached server certificate path can be omitted from the TLS previously cached server certificate path can be omitted from the TLS
handshake. handshake.
This specification defines the Cached Information TLS extension, This specification defines the Cached Information TLS extension,
which may be used by a client and a server to exclude transmission of which may be used by a client and a server to exclude transmission of
known cached parameters from the TLS handshake. cached information from the TLS handshake.
1.1. Terminology 1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Cached Information Extension 2. Cached Information Extension
A new extension type (cached_information(TBD)) is defined and used in A new extension type (cached_information(TBD)) is defined and used in
both the client hello and server hello messages. The extension type both the client hello and server hello messages. The extension type
is specified as follows. is specified as follows.
enum { enum {
cached_information(TBD), (65535) cached_information(TBD), (65535)
} ExtensionType; } ExtensionType;
The "extension_data" field of this extension, when included in the The extension_data field of this extension, when included in the
client hello, SHALL contain "CachedInformation" according to the client hello, SHALL contain CachedInformation according to the
following structure: following structure:
enum { enum {
certificate_chain(1), trusted_cas(2), (255) certificate_chain(1), trusted_cas(2), (255)
} CachedInformationType; } CachedInformationType;
struct { struct {
CachedInformationType type; CachedInformationType type;
opaque digest_value<0..8>; HashAlgorithm hash;
opaque hash_value<1..255>;
} CachedObject; } CachedObject;
struct { struct {
CachedObject cached_info<1..2048>; CachedObject cached_info<1..2^16-1>;
} CachedInformation; } CachedInformation;
The digest_value of a CachedObject MUST either be empty (0 bytes) or
contain a 64 bit FNV digest (8 bytes) as specified in Annex A. The 64
bit integer is represented as an 8 byte digest_value in big-endian
order (with most significant bits in the first byte and least
significant bits in the last byte).
When CachedInformationType identifies certificate_chain, then When CachedInformationType identifies certificate_chain, then
digest_value MUST include a digest calculated over the hash_value MUST include a hash calculated over the certificate_list
certificate_list element of a server side Certificate message, element of a server side Certificate message, excluding the three
excluding the three length bytes of the certificate_list vector. length bytes of the certificate_list vector.
When CachedInformationType identifies trusted_cas, then digest_value When CachedInformationType identifies trusted_cas, then hash_value
MUST include a digest calculated over the certificate_authorities MUST include a hash calculated over the certificate_authorities
element of a server side CertificateRequest message, excluding the element of a server side CertificateRequest message, excluding the
two length bytes of the certificate_authorities vector. two length bytes of the certificate_authorities vector.
The hash algorithm used to calculate hash values SHALL be the hash
algorithm that was used to generate the Finished message in the
handshake exchange from which the hashed information was cached. Hash
algorithm identifiers are defined in the RFC 5246 [RFC5246]
HashAlgorithm registry.
Other specifications MAY define more CachedInformationType types. Other specifications MAY define more CachedInformationType types.
3. Extension Exchange 3. Extension Exchange
3.1. Reconnaissance 3.1. Cached Information
A client MAY include an empty cached_information extension (with
empty extension_data field) in its (extended) client hello to query
whether the server supports cached information.
A server indicates that it supports cached information in handshakes
according to section 3.2. by including a cached_information extension
in its (extended) server hello.
3.2. Cached Information
Clients MAY specify cached information from previous handshakes by Clients MAY include a "cached_information" extension in the
including a "cached_information" extension in the (extended) client (extended) client hello, which MAY contain zero or more cached
hello, which contains at least one cached object (CachedObject) for objects (CachedObject).
each present object type (CachedInformationType), as specified in
section 2. Clients MAY need the ability to cache different values
depending on other information in the Client Hello that modify what
values the server uses, in particular the Server Name Indication
[RFC4366] value. Clients sending a non-empty cached_information
extension MUST provide a 64 bit (8 byte) digest_value for each cached
object.
Servers that receive an extended client hello containing a Servers that receive an extended client hello containing a
"cached_information" extension, MAY indicate that they support "cached_information" extension MAY indicate that they support cached
caching of information objects by including an cached_information information objects by including a cached_information extension in
extension in their (extended) server hello. their (extended) server hello.
A cached_information extension provided in the server hello has the A cached_information extension provided in the server hello has the
following semantics: following semantics:
o An empty cached_information extension indicates that the server o An empty cached_information extension indicates that the server
supports information caching but provides no information about supports information caching but provides no information about
what information types it supports. what information types it supports.
o A non-empty cached information extension indicates that the o A non-empty cached information extension indicates that the
server supports only those CachedInformationType types that are server supports caching of each present CachedObject that matches
identified by each present CachedObject. the specified hash value. The server MAY support other cached
objects that are not present in the extension.
o A CachedObject with an empty digest_value indicates that the Note: Clients may need the ability to cache different values
server supports caching of the specified object type depending on other information in the Client Hello that modify what
(CachedInformationType), but does not specify any digest values values the server uses, in particular the Server Name Indication
it will accept. [RFC4366] value.
o A present non-empty digest_value indicates that the server will 3.2. Reconnaissance
honor caching of objects of the specified type that matches the
present digest value.
4. Data Substitution A client MAY include an empty cached_information extension (with
empty extension_data field) in its (extended) client hello to query
whether the server supports cached information.
Upon receiving an empty cached_information extension, a server MAY
indicate that it supports cached information in handshakes by
including a cached_information extension in its (extended) server
hello according to any of the available options in section 3.1.
4. Cached Information Substitution
Following a successful exchange of "cached_information" extensions, Following a successful exchange of "cached_information" extensions,
the server may substitute data objects in the handshake exchange with the server MAY substitute cached information in the handshake
a matching digest_value representing a matching object type. received exchange with a matching CachedObject from the client hello
from the client in its client hello. "cached_information" extension.
The handshake protocol will proceed using the cached data as if it A substitution syntax that defines how the CachedObject structure is
was provided in the handshake protocol. The Finished message will carried in the handshake message MUST be defined for each
however be calculated over the actual data exchanged in the handshake CachedInformationType in a way that does not violate the syntax of
protocol. That is, the Finished message will be calculated over the the handshake message. The substitution syntax for
digest values of cached information objects and not over the cached certificate_chain(1) and trusted_cas(2) is provided below.
objects that were omitted from transmission.
Each CachedInformationType MUST specify how actual data is replaced The handshake protocol SHALL proceed using the cached information as
by a digest in a way that does not violate the defined syntax of if it was provided in the handshake protocol. The Finished message
existing handshake messages. the data exchange syntax for SHALL be calculated over the actual data exchanged in the handshake
certificate_chain(1) and trusted_cas(2) are provided below. protocol. That is, the Finished message will be calculated over the
hash values of cached information objects and not over the cached
information that were omitted from transmission.
The server MUST NOT provide more than one digest value as The server MUST NOT include more than one CachedObject as
substitution for the cached data. substitution for the cached information.
4.1. Data Substitution Syntax for certificate_chain 4.1. Substitution Syntax for certificate_chain
When a digest for an object of type certificate_chain is provided in When an object of type certificate_chain is provided in the client
the client hello, the server MAY substitute the cached data with a hello, the server MAY substitute the cached information with a
matching digest value received from the client by expanding the matching hash value received from the client by expanding the
Certificate handshake message as follows. Certificate handshake message as follows.
Original handshake message syntax defined in RFC 5246 [RFC5246]: Original handshake message syntax defined in RFC 5246 [RFC5246]:
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;
Substitution syntax is defined by expanding the definition of the Substitution syntax is defined by expanding the syntax of the opaque
opaque ASN.1Cert structure: ASN.1Cert structure:
DigestInfo ASN.1Cert<1..2^24-1>;
struct { CachedObject ASN.1Cert<1..2^24-1>;
opaque digest_value<0..8>;
} DigestInfo;
4.2. Data Substitution Syntax for trusted_cas 4.2. Substitution Syntax for trusted_cas
When a digest for an object of type trusted_cas is provided in the When a hash for an object of type trusted_cas is provided in the
client hello, the server MAY substitute the cached data with a client hello, the server MAY substitute the cached information with a
matching digest value received from the client by expanding the matching hash value received from the client by expanding the
CertificateRequest handshake message as follows. CertificateRequest handshake message as follows.
Original handshake message syntax defined in RFC 5246 [RFC5246]: Original handshake message syntax defined in RFC 5246 [RFC5246]:
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 SignatureAndHashAlgorithm
supported_signature_algorithms<2^16-1>; supported_signature_algorithms<2^16-1>;
DistinguishedName certificate_authorities<0..2^16-1>; DistinguishedName certificate_authorities<0..2^16-1>;
} CertificateRequest } CertificateRequest
The substitution syntax is defined by expanding the definition of the The substitution syntax is defined by expanding the syntax of the
opaque DistinguishedName structure: opaque DistinguishedName structure:
DigestInfo DistinguishedName<1..2^16-1>; CachedObject DistinguishedName<1..2^16-1>;
struct {
opaque digest_value<0..8>;
} DigestInfo;
5. Security Considerations 5. Security Considerations
The digest algorithm used in this specification is required to have The hash algorithm used in this specification is required to have
reasonable random properties in order to provide reasonably unique reasonable random properties in order to provide reasonably unique
identifiers. There is no requirement that this digest algorithm must identifiers. There is no clearly identified requirement that this
have strong collision resistance. A non unique digest may at most hash algorithm must have strong collision resistance. However since
lead to a failed TLS handshake followed by a new attempt without the the hash algorithm is used to represent data in the finished
cached information extension. There are no identified security calculation, the security properties of the finished calculation will
threats that require the selected digest algorithm to have strong change if a weaker hash algorithm is used to represent cached
collision resistance. information compared with the hash algorithm used to calculate the
finished message.
Caching information in an encrypted handshake (such as a renegotiated
handshake) and sending a hash of that cached information in an
unencrypted handshake might introduce integrity or data disclosure
issues as it enables an attacker to identify if a known object (such
as a known server certificate) has been used in previous encrypted
handshakes. Information object types defined in this specification,
such as server certificates, are public objects and usually not
sensitive in this regard, but implementers should be aware if any
cached information are subject to such security concerns and in such
case SHOULD NOT send a hash over encrypted data in en unencrypted
handshake.
6. IANA Considerations 6. IANA Considerations
1) Create an entry, cached_information(TBD), in the existing registry 1) Create an entry, cached_information(TBD), in the existing registry
for ExtensionType (defined in RFC 5246 [RFC5246]). for ExtensionType (defined in RFC 5246 [RFC5246]).
2) Establish a registry for TLS CachedInformationType values. The 2) Establish a registry for TLS CachedInformationType values. The
first entries in the registry are certificate_chain(1) and first entries in the registry are certificate_chain(1) and
trusted_cas(2). TLS CachedInformationType values in the inclusive trusted_cas(2). TLS CachedInformationType values in the inclusive
range 0-63 (decimal) are assigned via RFC 5226 [RFC5226] Standards range 0-63 (decimal) are assigned via RFC 5226 [RFC5226] Standards
Action. Values from the inclusive range 64-223 (decimal) are Action. Values from the inclusive range 64-223 (decimal) are
assigned via RFC 5226 Specification Required. Values from the assigned via RFC 5226 Specification Required. Values from the
inclusive range 224-255 (decimal) are reserved for RFC 5226 inclusive range 224-255 (decimal) are reserved for RFC 5226
Private Use. Private Use.
7. Acknowledgements 7. Acknowledgements
The author acknowledge input from many members of the TLS working The author acknowledges input from many members of the TLS working
group, Martin Rex for extensive review and input, Marsh Ray and Simon group.
Josefsson for coding and test vectors.
8. Normative References 8. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997 Requirement Levels", BCP 14, RFC 2119, March 1997
[RFC5226] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA [RFC5226] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 5226, May 2008 Considerations Section in RFCs", RFC 5226, May 2008
[RFC5246] T. Dierks, E. Rescorla, "The Transport Layer Security [RFC5246] T. Dierks, E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008 (TLS) Protocol Version 1.2", RFC 5246, August 2008
[RFC4366] S. Blake-Wilson, M. Nystrom, D. Hopwood, J. Mikkelsen, T. [RFC4366] S. Blake-Wilson, M. Nystrom, D. Hopwood, J. Mikkelsen, T.
Wright, "Transport Layer Security (TLS) Extensions", RFC Wright, "Transport Layer Security (TLS) Extensions", RFC
4366, April 2006 4366, April 2006
NOTE: RFC 4366 will be updated by RFC4366bis, currently in IESG NOTE: RFC 4366 will be updated by RFC4366bis, currently in IESG
process. process.
Annex A - 64 bit FNV-1a digest
A.1. Definition (Normative)
FNV-1 digest algorithm is a non-cryptographic hash function created
by Glenn Fowler, Landon Curt Noll, and Phong Vo. The FNV digest
algorithms and sample FNV source code have been released into the
public domain. FNV-1 has two defined variants, FNV-1 and FNV-1a. The
algorithm specified in this annex specifies the FNV-1a variant.
The FNV-1a digest is generated as follows:
digest = FNV_offset_basis
for each octet_of_data to be digested {
digest = digest XOR octet_of_data
digest = digest * FNV_prime }
return digest
In the above pseudocode, all variables are unsigned integers. All
variables, except for octet_of_data, have the same number of bits as
the FNV digest (64 Bits). The variable, octet_of_data, is an 8 bit
unsigned integer. Specifically for a 64 bit FNV-1a digest the
following applies:
o All variables, except for octet_of_data, are 64-bit unsigned
integers.
o The variable, octet_of_data, is an 8 bit unsigned integer.
o The FNV_offset_basis is the 64-bit FNV offset basis value:
14695981039346656037.
o The FNV_prime is the 64-bit FNV prime value: 1099511628211.
o The multiply function (indicated by the '*' symbol) returns the
lower 64-bits of the product.
o The XOR is an 8-bit operation that modifies only the lower 8-bits
of the digest value.
o The digest value returned is an 64-bit unsigned integer.
A.2 Java code sample (Informative)
/**
* Java code sample, implementing 64 bit FNV-1a
* By Stefan Santesson
*/
import java.math.BigInteger;
public class FNV {
static public BigInteger getFNV1a64Digest (String inpString) {
BigInteger m = new BigInteger("2").pow(64);
BigInteger fnvPrime = new BigInteger("1099511628211");
BigInteger fnvOffsetBasis = new BigInteger
("14695981039346656037");
BigInteger digest = fnvOffsetBasis;
for (int i = 0; i < inpString.length(); i++) {
digest = digest.xor(BigInteger.valueOf(
(int) inpString.charAt(i)));
digest = digest.multiply(fnvPrime).mod(m);
}
return (digest);
}
}
A.3. C code sample (Informative)
fnv1a64.h:
#ifndef FNV1A64_H
#define FNV1A64_H
#include <string.h> /* For size_t */
#include <stdint.h> /* For uint64_t */
extern uint64_t fnv1a64 (const uint8_t *buffer, size_t len);
#endif
fnv1a64.c:
/* fnv1a.c -- Implementation of the FNV-1A non-cryptographic
* hash function.
* By Simon Josefsson <simon@josefsson.org> on 2010-03-30.
*/
#include "fnv1a64.h"
#define FNV1A64_OFFSET_BASIS 14695981039346656037ULL
#define FNV1A64_PRIME 1099511628211ULL
uint64_t
fnv1a64 (const uint8_t *buffer, size_t len)
{
uint64_t hash;
size_t i;
hash = FNV1A64_OFFSET_BASIS;
for (i = 0; i < len; i++)
{
hash = hash ^ buffer[i];
hash = hash * FNV1A64_PRIME;
}
return hash;
}
A.4. Digest samples (Informative)
Digest samples for 64 bit FNV-1a
For input data:
null ("")
0 bytes
Digest is: CB F2 9C E4 84 22 23 25
For input data:
hex: 61 ("a")
1 byte
Digest is: AF 63 DC 4C 86 01 EC 8C
For input data:
hex: FF 00 00 01
4 bytes
Digest is: 69 61 19 64 91 CC 68 2D
For input data:
hex: 68 74 74 70 3A 2F 2F 65 6E 2E 77 69 6B 69 70 65
64 69 61 2E 6F 72 67 2F 77 69 6B 69 2F 46 6F 77
6C 65 72 5F 4E 6F 6C 6C 5F 56 6F 5F 68 61 73 68
("http://en.wikipedia.org/wiki/Fowler_Noll_Vo_hash")
48 bytes
Digest is: D9 B9 57 FB 7F E7 94 C5
Authors' Addresses Authors' Addresses
Stefan Santesson Stefan Santesson
3xA Security AB 3xA Security AB
Bjornstorp 744 Scheelev. 17
247 98 Genarp 223 70 Sweden
Sweden
EMail: sts@aaa-sec.com EMail: sts@aaa-sec.com
 End of changes. 37 change blocks. 
261 lines changed or deleted 106 lines changed or added

This html diff was produced by rfcdiff 1.38. The latest version is available from http://tools.ietf.org/tools/rfcdiff/