draft-ietf-tls-tls13-15.txt   draft-ietf-tls-tls13-16.txt 
Network Working Group E. Rescorla Network Working Group E. Rescorla
Internet-Draft RTFM, Inc. Internet-Draft RTFM, Inc.
Obsoletes: 5077, 5246, 5746 (if August 17, 2016 Obsoletes: 5077, 5246, 5746 (if September 22, 2016
approved) approved)
Updates: 4492, 6066, 6961 (if approved) Updates: 4492, 5705, 6066, 6961 (if
approved)
Intended status: Standards Track Intended status: Standards Track
Expires: February 18, 2017 Expires: March 26, 2017
The Transport Layer Security (TLS) Protocol Version 1.3 The Transport Layer Security (TLS) Protocol Version 1.3
draft-ietf-tls-tls13-15 draft-ietf-tls-tls13-16
Abstract Abstract
This document specifies version 1.3 of the Transport Layer Security This document specifies version 1.3 of the Transport Layer Security
(TLS) protocol. TLS allows client/server applications to communicate (TLS) protocol. TLS allows client/server applications to communicate
over the Internet in a way that is designed to prevent eavesdropping, over the Internet in a way that is designed to prevent eavesdropping,
tampering, and message forgery. tampering, and message forgery.
Status of This Memo Status of This Memo
skipping to change at page 1, line 36 skipping to change at page 1, line 37
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 18, 2017. This Internet-Draft will expire on March 26, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 5 1.1. Conventions and Terminology . . . . . . . . . . . . . . . 5
1.2. Major Differences from TLS 1.2 . . . . . . . . . . . . . 6 1.2. Major Differences from TLS 1.2 . . . . . . . . . . . . . 6
1.3. Updates Affecting TLS 1.2 . . . . . . . . . . . . . . . . 11 1.3. Updates Affecting TLS 1.2 . . . . . . . . . . . . . . . . 12
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 12
2.1. Incorrect DHE Share . . . . . . . . . . . . . . . . . . . 14 2.1. Incorrect DHE Share . . . . . . . . . . . . . . . . . . . 15
2.2. Resumption and Pre-Shared Key (PSK) . . . . . . . . . . . 15 2.2. Resumption and Pre-Shared Key (PSK) . . . . . . . . . . . 16
2.3. Zero-RTT Data . . . . . . . . . . . . . . . . . . . . . . 17 2.3. Zero-RTT Data . . . . . . . . . . . . . . . . . . . . . . 18
3. Presentation Language . . . . . . . . . . . . . . . . . . . . 18 3. Presentation Language . . . . . . . . . . . . . . . . . . . . 19
3.1. Basic Block Size . . . . . . . . . . . . . . . . . . . . 18 3.1. Basic Block Size . . . . . . . . . . . . . . . . . . . . 19
3.2. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 19 3.2. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 20
3.3. Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.3. Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.5. Enumerateds . . . . . . . . . . . . . . . . . . . . . . . 20 3.5. Enumerateds . . . . . . . . . . . . . . . . . . . . . . . 21
3.6. Constructed Types . . . . . . . . . . . . . . . . . . . . 21 3.6. Constructed Types . . . . . . . . . . . . . . . . . . . . 22
3.6.1. Variants . . . . . . . . . . . . . . . . . . . . . . 21 3.6.1. Variants . . . . . . . . . . . . . . . . . . . . . . 22
3.7. Constants . . . . . . . . . . . . . . . . . . . . . . . . 23 3.7. Constants . . . . . . . . . . . . . . . . . . . . . . . . 23
4. Handshake Protocol . . . . . . . . . . . . . . . . . . . . . 23 3.8. Decoding Errors . . . . . . . . . . . . . . . . . . . . . 24
4.1. Key Exchange Messages . . . . . . . . . . . . . . . . . . 24 4. Handshake Protocol . . . . . . . . . . . . . . . . . . . . . 24
4.1.1. Cryptographic Negotiation . . . . . . . . . . . . . . 25 4.1. Key Exchange Messages . . . . . . . . . . . . . . . . . . 25
4.1.2. Client Hello . . . . . . . . . . . . . . . . . . . . 26 4.1.1. Cryptographic Negotiation . . . . . . . . . . . . . . 26
4.1.3. Server Hello . . . . . . . . . . . . . . . . . . . . 28 4.1.2. Client Hello . . . . . . . . . . . . . . . . . . . . 27
4.1.4. Hello Retry Request . . . . . . . . . . . . . . . . . 29 4.1.3. Server Hello . . . . . . . . . . . . . . . . . . . . 29
4.2. Hello Extensions . . . . . . . . . . . . . . . . . . . . 31 4.1.4. Hello Retry Request . . . . . . . . . . . . . . . . . 31
4.2.1. Cookie . . . . . . . . . . . . . . . . . . . . . . . 32 4.2. Hello Extensions . . . . . . . . . . . . . . . . . . . . 32
4.2.2. Signature Algorithms . . . . . . . . . . . . . . . . 33 4.2.1. Supported Versions . . . . . . . . . . . . . . . . . 34
4.2.3. Negotiated Groups . . . . . . . . . . . . . . . . . . 36 4.2.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . 35
4.2.4. Key Share . . . . . . . . . . . . . . . . . . . . . . 37 4.2.3. Signature Algorithms . . . . . . . . . . . . . . . . 35
4.2.5. Pre-Shared Key Extension . . . . . . . . . . . . . . 39 4.2.4. Negotiated Groups . . . . . . . . . . . . . . . . . . 38
4.2.6. Early Data Indication . . . . . . . . . . . . . . . . 41 4.2.5. Key Share . . . . . . . . . . . . . . . . . . . . . . 39
4.2.7. OCSP Status Extensions . . . . . . . . . . . . . . . 44 4.2.6. Pre-Shared Key Extension . . . . . . . . . . . . . . 42
4.2.8. Encrypted Extensions . . . . . . . . . . . . . . . . 45 4.2.7. Early Data Indication . . . . . . . . . . . . . . . . 43
4.2.9. Certificate Request . . . . . . . . . . . . . . . . . 45 4.2.8. OCSP Status Extensions . . . . . . . . . . . . . . . 47
4.3. Authentication Messages . . . . . . . . . . . . . . . . . 47 4.3. Server Parameters Messages . . . . . . . . . . . . . . . 47
4.3.1. Certificate . . . . . . . . . . . . . . . . . . . . . 49 4.3.1. Encrypted Extensions . . . . . . . . . . . . . . . . 47
4.3.2. Certificate Verify . . . . . . . . . . . . . . . . . 52 4.3.2. Certificate Request . . . . . . . . . . . . . . . . . 48
4.3.3. Finished . . . . . . . . . . . . . . . . . . . . . . 54 4.4. Authentication Messages . . . . . . . . . . . . . . . . . 50
4.4. Post-Handshake Messages . . . . . . . . . . . . . . . . . 55 4.4.1. Certificate . . . . . . . . . . . . . . . . . . . . . 51
4.4.1. New Session Ticket Message . . . . . . . . . . . . . 56 4.4.2. Certificate Verify . . . . . . . . . . . . . . . . . 54
4.4.2. Post-Handshake Authentication . . . . . . . . . . . . 57 4.4.3. Finished . . . . . . . . . . . . . . . . . . . . . . 56
4.4.3. Key and IV Update . . . . . . . . . . . . . . . . . . 58 4.5. Post-Handshake Messages . . . . . . . . . . . . . . . . . 58
4.5. Handshake Layer and Key Changes . . . . . . . . . . . . . 59 4.5.1. New Session Ticket Message . . . . . . . . . . . . . 58
5. Record Protocol . . . . . . . . . . . . . . . . . . . . . . . 59 4.5.2. Post-Handshake Authentication . . . . . . . . . . . . 60
5.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 59 4.5.3. Key and IV Update . . . . . . . . . . . . . . . . . . 60
5.2. Record Payload Protection . . . . . . . . . . . . . . . . 61 4.6. Handshake Layer and Key Changes . . . . . . . . . . . . . 61
5.3. Per-Record Nonce . . . . . . . . . . . . . . . . . . . . 63 5. Record Protocol . . . . . . . . . . . . . . . . . . . . . . . 61
5.4. Record Padding . . . . . . . . . . . . . . . . . . . . . 63 5.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 62
5.5. Limits on Key Usage . . . . . . . . . . . . . . . . . . . 64 5.2. Record Payload Protection . . . . . . . . . . . . . . . . 63
6. Alert Protocol . . . . . . . . . . . . . . . . . . . . . . . 65 5.3. Per-Record Nonce . . . . . . . . . . . . . . . . . . . . 65
6.1. Closure Alerts . . . . . . . . . . . . . . . . . . . . . 66 5.4. Record Padding . . . . . . . . . . . . . . . . . . . . . 66
6.2. Error Alerts . . . . . . . . . . . . . . . . . . . . . . 67 5.5. Limits on Key Usage . . . . . . . . . . . . . . . . . . . 67
7. Cryptographic Computations . . . . . . . . . . . . . . . . . 70 6. Alert Protocol . . . . . . . . . . . . . . . . . . . . . . . 67
7.1. Key Schedule . . . . . . . . . . . . . . . . . . . . . . 70 6.1. Closure Alerts . . . . . . . . . . . . . . . . . . . . . 68
7.2. Updating Traffic Keys and IVs . . . . . . . . . . . . . . 73 6.2. Error Alerts . . . . . . . . . . . . . . . . . . . . . . 70
7.3. Traffic Key Calculation . . . . . . . . . . . . . . . . . 73 7. Cryptographic Computations . . . . . . . . . . . . . . . . . 72
7.3.1. Diffie-Hellman . . . . . . . . . . . . . . . . . . . 74 7.1. Key Schedule . . . . . . . . . . . . . . . . . . . . . . 72
7.3.2. Elliptic Curve Diffie-Hellman . . . . . . . . . . . . 75 7.2. Updating Traffic Keys and IVs . . . . . . . . . . . . . . 75
7.3.3. Exporters . . . . . . . . . . . . . . . . . . . . . . 75 7.3. Traffic Key Calculation . . . . . . . . . . . . . . . . . 75
8. Compliance Requirements . . . . . . . . . . . . . . . . . . . 75 7.3.1. Diffie-Hellman . . . . . . . . . . . . . . . . . . . 76
8.1. MTI Cipher Suites . . . . . . . . . . . . . . . . . . . . 76 7.3.2. Elliptic Curve Diffie-Hellman . . . . . . . . . . . . 77
8.2. MTI Extensions . . . . . . . . . . . . . . . . . . . . . 76 7.3.3. Exporters . . . . . . . . . . . . . . . . . . . . . . 77
9. Security Considerations . . . . . . . . . . . . . . . . . . . 77 8. Compliance Requirements . . . . . . . . . . . . . . . . . . . 78
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 77 8.1. MTI Cipher Suites . . . . . . . . . . . . . . . . . . . . 78
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 80 8.2. MTI Extensions . . . . . . . . . . . . . . . . . . . . . 78
11.1. Normative References . . . . . . . . . . . . . . . . . . 80 9. Security Considerations . . . . . . . . . . . . . . . . . . . 79
11.2. Informative References . . . . . . . . . . . . . . . . . 83 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 79
Appendix A. Protocol Data Structures and Constant Values . . . . 90 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 83
A.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 90 11.1. Normative References . . . . . . . . . . . . . . . . . . 83
A.2. Alert Messages . . . . . . . . . . . . . . . . . . . . . 90 11.2. Informative References . . . . . . . . . . . . . . . . . 85
A.3. Handshake Protocol . . . . . . . . . . . . . . . . . . . 92 Appendix A. Protocol Data Structures and Constant Values . . . . 93
A.3.1. Key Exchange Messages . . . . . . . . . . . . . . . . 92 A.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 93
A.3.2. Server Parameters Messages . . . . . . . . . . . . . 96 A.2. Alert Messages . . . . . . . . . . . . . . . . . . . . . 93
A.3.3. Authentication Messages . . . . . . . . . . . . . . . 97 A.3. Handshake Protocol . . . . . . . . . . . . . . . . . . . 95
A.3.4. Ticket Establishment . . . . . . . . . . . . . . . . 97 A.3.1. Key Exchange Messages . . . . . . . . . . . . . . . . 95
A.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 98 A.3.2. Server Parameters Messages . . . . . . . . . . . . . 99
A.4.1. Unauthenticated Operation . . . . . . . . . . . . . . 99 A.3.3. Authentication Messages . . . . . . . . . . . . . . . 100
Appendix B. Implementation Notes . . . . . . . . . . . . . . . . 100 A.3.4. Ticket Establishment . . . . . . . . . . . . . . . . 100
B.1. API considerations for 0-RTT . . . . . . . . . . . . . . 100 A.3.5. Updating Keys . . . . . . . . . . . . . . . . . . . . 101
B.2. Random Number Generation and Seeding . . . . . . . . . . 100
B.3. Certificates and Authentication . . . . . . . . . . . . . 100 A.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 101
B.4. Cipher Suite Support . . . . . . . . . . . . . . . . . . 100 Appendix B. Implementation Notes . . . . . . . . . . . . . . . . 102
B.5. Implementation Pitfalls . . . . . . . . . . . . . . . . . 101 B.1. API considerations for 0-RTT . . . . . . . . . . . . . . 102
B.6. Client Tracking Prevention . . . . . . . . . . . . . . . 102 B.2. Random Number Generation and Seeding . . . . . . . . . . 102
Appendix C. Backward Compatibility . . . . . . . . . . . . . . . 102 B.3. Certificates and Authentication . . . . . . . . . . . . . 103
C.1. Negotiating with an older server . . . . . . . . . . . . 103 B.4. Cipher Suite Support . . . . . . . . . . . . . . . . . . 103
C.2. Negotiating with an older client . . . . . . . . . . . . 104 B.5. Implementation Pitfalls . . . . . . . . . . . . . . . . . 103
C.3. Zero-RTT backwards compatibility . . . . . . . . . . . . 104 B.6. Client Tracking Prevention . . . . . . . . . . . . . . . 105
C.4. Backwards Compatibility Security Restrictions . . . . . . 105 B.7. Unauthenticated Operation . . . . . . . . . . . . . . . . 105
Appendix D. Overview of Security Properties . . . . . . . . . . 106 Appendix C. Backward Compatibility . . . . . . . . . . . . . . . 105
D.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 106 C.1. Negotiating with an older server . . . . . . . . . . . . 106
D.2. Record Layer . . . . . . . . . . . . . . . . . . . . . . 108 C.2. Negotiating with an older client . . . . . . . . . . . . 107
Appendix E. Working Group Information . . . . . . . . . . . . . 109 C.3. Zero-RTT backwards compatibility . . . . . . . . . . . . 107
Appendix F. Contributors . . . . . . . . . . . . . . . . . . . . 109 C.4. Backwards Compatibility Security Restrictions . . . . . . 108
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 113 Appendix D. Overview of Security Properties . . . . . . . . . . 109
D.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 109
D.2. Record Layer . . . . . . . . . . . . . . . . . . . . . . 111
Appendix E. Working Group Information . . . . . . . . . . . . . 112
Appendix F. Contributors . . . . . . . . . . . . . . . . . . . . 113
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 117
1. Introduction 1. Introduction
DISCLAIMER: This is a WIP draft of TLS 1.3 and has not yet seen DISCLAIMER: This is a WIP draft of TLS 1.3 and has not yet seen
significant security analysis. significant security analysis.
RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH The source for this RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH The source for this
draft is maintained in GitHub. Suggested changes should be submitted draft is maintained in GitHub. Suggested changes should be submitted
as pull requests at https://github.com/tlswg/tls13-spec. as pull requests at https://github.com/tlswg/tls13-spec.
Instructions are on that page as well. Editorial changes can be Instructions are on that page as well. Editorial changes can be
managed in GitHub, but any substantive change should be discussed on managed in GitHub, but any substantive change should be discussed on
the TLS mailing list. the TLS mailing list.
The primary goal of TLS is to provide a secure channel between two The primary goal of TLS is to provide a secure channel between two
communicating peers. Specifically, the channel should provide the communicating peers. Specifically, the channel should provide the
following properties. following properties:
- Authentication: The server side of the channel is always - Authentication: The server side of the channel is always
authenticated; the client side is optionally authenticated. authenticated; the client side is optionally authenticated.
Authentication can happen via asymmetric cryptography (e.g., RSA Authentication can happen via asymmetric cryptography (e.g., RSA
[RSA], ECDSA [ECDSA]) or a pre-shared symmetric key. [RSA], ECDSA [ECDSA]) or a pre-shared symmetric key.
- Confidentiality: Data sent over the channel is not visible to - Confidentiality: Data sent over the channel is not visible to
attackers. attackers.
- Integrity: Data sent over the channel cannot be modified by - Integrity: Data sent over the channel cannot be modified by
attackers. attackers.
These properties should be true even in the face of an attacker who These properties should be true even in the face of an attacker who
has complete control of the network, as described in [RFC3552]. See has complete control of the network, as described in [RFC3552]. See
Appendix D for a more complete statement of the relevant security Appendix D for a more complete statement of the relevant security
properties. properties.
TLS consists of two primary components: TLS consists of two primary components:
- A handshake protocol (Section 4) which authenticates the - A handshake protocol (Section 4) that authenticates the
communicating parties, negotiates cryptographic modes and communicating parties, negotiates cryptographic modes and
parameters, and establishes shared keying material. The handshake parameters, and establishes shared keying material. The handshake
protocol is designed to resist tampering; an active attacker protocol is designed to resist tampering; an active attacker
should not be able to force the peers to negotiate different should not be able to force the peers to negotiate different
parameters than they would if the connection were not under parameters than they would if the connection were not under
attack. attack.
- A record protocol (Section 5) which uses the parameters - A record protocol (Section 5) that uses the parameters established
established by the handshake protocol to protect traffic between by the handshake protocol to protect traffic between the
the communicating peers. The record protocol divides traffic up communicating peers. The record protocol divides traffic up into
into a series of records, each of which is independently protected a series of records, each of which is independently protected
using the traffic keys. using the traffic keys.
TLS is application protocol independent; higher-level protocols can TLS is application protocol independent; higher-level protocols can
layer on top of TLS transparently. The TLS standard, however, does layer on top of TLS transparently. The TLS standard, however, does
not specify how protocols add security with TLS; the decisions on how not specify how protocols add security with TLS; how to initiate TLS
to initiate TLS handshaking and how to interpret the authentication handshaking and how to interpret the authentication certificates
certificates exchanged are left to the judgment of the designers and exchanged are left to the judgment of the designers and implementors
implementors of protocols that run on top of TLS. of protocols that run on top of TLS.
This document defines TLS version 1.3. While TLS 1.3 is not directly This document defines TLS version 1.3. While TLS 1.3 is not directly
compatible with previous versions, all versions of TLS incorporate a compatible with previous versions, all versions of TLS incorporate a
versioning mechanism which allows clients and servers to versioning mechanism which allows clients and servers to
interoperably negotiate a common version if one is supported. interoperably negotiate a common version if one is supported.
1.1. Conventions and Terminology 1.1. Conventions and 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", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
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session: An association between a client and a server resulting from session: An association between a client and a server resulting from
a handshake. a handshake.
server: The endpoint which did not initiate the TLS connection. server: The endpoint which did not initiate the TLS connection.
1.2. Major Differences from TLS 1.2 1.2. Major Differences from TLS 1.2
(*) indicates changes to the wire protocol which may require (*) indicates changes to the wire protocol which may require
implementations to update. implementations to update.
draft-16
- Change RSASSA-PSS and EdDSA SignatureScheme codepoints for better
backwards compatibility (*)
- Move HelloRetryRequest.selected_group to an extension (*)
- Clarify the behavior of no exporter context and make it the same
as an empty context.(*)
- New KeyUpdate format that allows for requesting/not-requesting an
answer (*)
- New certificate_required alert (*)
- Forbid CertificateRequest with 0-RTT and PSK.
- Relax requirement to check SNI for 0-RTT.
draft-15 draft-15
- New negotiation syntax as discussed in Berlin (*) - New negotiation syntax as discussed in Berlin (*)
- Require CertificateRequest.context to be empty during handshake - Require CertificateRequest.context to be empty during handshake
(*) (*)
- Forbid empty tickets (*) - Forbid empty tickets (*)
- Forbid application data messages in between post-handshake - Forbid application data messages in between post-handshake
messages from the same flight (*) messages from the same flight (*)
- Clean up alert guidance (*) - Clean up alert guidance (*)
- Clearer guidance on what is needed for TLS 1.2. - Clearer guidance on what is needed for TLS 1.2.
- Guidance on 0-RTT time windows. - Guidance on 0-RTT time windows.
- Rename a bunch of fields. - Rename a bunch of fields.
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algorithm, and curve together. This is backwards compatible. algorithm, and curve together. This is backwards compatible.
- Make ticket lifetime mandatory and limit it to a week. - Make ticket lifetime mandatory and limit it to a week.
- Make the purpose strings lower-case. This matches how people are - Make the purpose strings lower-case. This matches how people are
implementing for interop. implementing for interop.
- Define exporters. - Define exporters.
- Editorial cleanup - Editorial cleanup
draft-11
- Port the CFRG curves & signatures work from RFC4492bis. - Port the CFRG curves & signatures work from RFC4492bis.
- Remove sequence number and version from additional_data, which is - Remove sequence number and version from additional_data, which is
now empty. now empty.
- Reorder values in HkdfLabel. - Reorder values in HkdfLabel.
- Add support for version anti-downgrade mechanism. - Add support for version anti-downgrade mechanism.
- Update IANA considerations section and relax some of the policies. - Update IANA considerations section and relax some of the policies.
skipping to change at page 10, line 33 skipping to change at page 11, line 5
draft-06 draft-06
- Prohibit RC4 negotiation for backwards compatibility. - Prohibit RC4 negotiation for backwards compatibility.
- Freeze & deprecate record layer version field. - Freeze & deprecate record layer version field.
- Update format of signatures with context. - Update format of signatures with context.
- Remove explicit IV. - Remove explicit IV.
draft-05
- Prohibit SSL negotiation for backwards compatibility. - Prohibit SSL negotiation for backwards compatibility.
- Fix which MS is used for exporters. - Fix which MS is used for exporters.
draft-04 draft-04
- Modify key computations to include session hash. - Modify key computations to include session hash.
- Remove ChangeCipherSpec. - Remove ChangeCipherSpec.
skipping to change at page 11, line 38 skipping to change at page 12, line 13
- Remove support for non-AEAD ciphers. - Remove support for non-AEAD ciphers.
1.3. Updates Affecting TLS 1.2 1.3. Updates Affecting TLS 1.2
This document defines several changes that optionally affect This document defines several changes that optionally affect
implementations of TLS 1.2: implementations of TLS 1.2:
- A version downgrade protection mechanism is described in - A version downgrade protection mechanism is described in
Section 4.1.3. Section 4.1.3.
- RSASSA-PSS signature schemes are defined in Section 4.2.2. - RSASSA-PSS signature schemes are defined in Section 4.2.3.
An implementation of TLS 1.3 that also supports TLS 1.2 might need to An implementation of TLS 1.3 that also supports TLS 1.2 might need to
include changes to support these changes even when TLS 1.3 is not in include changes to support these changes even when TLS 1.3 is not in
use. See the referenced sections for more details. use. See the referenced sections for more details.
2. Protocol Overview 2. 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. When a TLS client and server first start TLS handshake protocol, which a TLS client and server use when first
communicating, they agree on a protocol version, select cryptographic communicating to agree on a protocol version, select cryptographic
algorithms, optionally authenticate each other, and establish shared algorithms, optionally authenticate each other, and establish shared
secret keying material. Once the handshake is complete, the peers secret keying material. Once the handshake is complete, the peers
use the established keys to protect application layer traffic. use the established keys to protect application layer traffic.
A failure of the handshake or other protocol error triggers the
termination of the connection, optionally preceded by an alert
message (Section 6).
TLS supports three basic key exchange modes: TLS supports three basic key exchange modes:
- Diffie-Hellman (of both the finite field and elliptic curve - Diffie-Hellman (both the finite field and elliptic curve
varieties). varieties),
- A pre-shared symmetric key (PSK) - A pre-shared symmetric key (PSK), and
- A combination of a symmetric key and Diffie-Hellman - A combination of a symmetric key and Diffie-Hellman.
Figure 1 below shows the basic full TLS handshake: Figure 1 below shows the basic full TLS handshake:
Client Server Client Server
Key ^ ClientHello Key ^ ClientHello
Exch | + key_share* Exch | + key_share*
v + pre_shared_key* --------> v + pre_shared_key* -------->
ServerHello ^ Key ServerHello ^ Key
+ key_share* | Exch + key_share* | Exch
skipping to change at page 12, line 49 skipping to change at page 13, line 38
messages that are not always sent. messages that are not always sent.
{} Indicates messages protected using keys {} Indicates messages protected using keys
derived from handshake_traffic_secret. derived from handshake_traffic_secret.
[] Indicates messages protected using keys [] Indicates messages protected using keys
derived from traffic_secret_N derived from traffic_secret_N
Figure 1: Message flow for full TLS Handshake Figure 1: Message flow for full TLS Handshake
The handshake can be thought of as having three phases, indicated in The handshake can be thought of as having three phases (indicated in
the diagram above. the diagram above):
- Key Exchange: Establish shared keying material and select the - Key Exchange: Establish shared keying material and select the
cryptographic parameters. Everything after this phase is cryptographic parameters. Everything after this phase is
encrypted. encrypted.
- Server Parameters: Establish other handshake parameters. (whether - Server Parameters: Establish other handshake parameters (whether
the client is authenticated, application layer protocol support, the client is authenticated, application layer protocol support,
etc.) etc.).
- Authentication: Authenticate the server (and optionally the - Authentication: Authenticate the server (and optionally the
client) and provide key confirmation and handshake integrity. client) and provide key confirmation and handshake integrity.
In the Key Exchange phase, the client sends the ClientHello In the Key Exchange phase, the client sends the ClientHello
(Section 4.1.2) message, which contains a random nonce (Section 4.1.2) message, which contains a random nonce
(ClientHello.random), its offered protocol version, a list of (ClientHello.random); its offered protocol versions; a list of
symmetric cipher/HKDF hash pairs, some set of Diffie-Hellman key symmetric cipher/HKDF hash pairs; some set of Diffie-Hellman key
shares (in the "key_share" extension Section 4.2.4), one or more pre- shares (in the "key_share" extension Section 4.2.5), one or more pre-
shared key labels (in the "pre_shared_key" extension Section 4.2.5), shared key labels (in the "pre_shared_key" extension Section 4.2.6),
or both, and potentially some other extensions. or both; and potentially some other extensions.
The server processes the ClientHello and determines the appropriate The server processes the ClientHello and determines the appropriate
cryptographic parameters for the connection. It then responds with cryptographic parameters for the connection. It then responds with
its own ServerHello which indicates the negotiated connection its own ServerHello, which indicates the negotiated connection
parameters. [Section 4.1.3]. The combination of the ClientHello and parameters. [Section 4.1.3]. The combination of the ClientHello and
the ServerHello determines the shared keys. If (EC)DHE key the ServerHello determines the shared keys. If (EC)DHE key
establishment is in use, then the ServerHello will contain a establishment is in use, then the ServerHello contains a "key_share"
"key_share" extension with the server's ephemeral Diffie-Hellman extension with the server's ephemeral Diffie-Hellman share which MUST
share which MUST be in the same group as one of the client's shares. be in the same group as one of the client's shares. If PSK key
If PSK key establishment is in use, then the ServerHello will contain establishment is in use, then the ServerHello contains a
a "pre_shared_key" extension indicating which of the client's offered "pre_shared_key" extension indicating which of the client's offered
PSKs was selected. Note that implementations can use (EC)DHE and PSK PSKs was selected. Note that implementations can use (EC)DHE and PSK
together, in which case both extensions will be supplied. together, in which case both extensions will be supplied.
The server then sends two messages to establish the Server The server then sends two messages to establish the Server
Parameters: Parameters:
EncryptedExtensions. responses to any extensions which are not EncryptedExtensions. responses to any extensions that are not
required in order to determine the cryptographic parameters. required to determine the cryptographic parameters.
[Section 4.2.8] [Section 4.3.1]
CertificateRequest. if certificate-based client authentication is CertificateRequest. if certificate-based client authentication is
desired, the desired parameters for that certificate. This desired, the desired parameters for that certificate. This
message will be omitted if client authentication is not desired. message is omitted if client authentication is not desired.
[Section 4.3.2]
Finally, the client and server exchange Authentication messages. TLS Finally, the client and server exchange Authentication messages. TLS
uses the same set of messages every time that authentication is uses the same set of messages every time that authentication is
needed. Specifically: needed. Specifically:
Certificate. the certificate of the endpoint. This message is Certificate. the certificate of the endpoint. This message is
omitted if the server is not authenticating with a certificate. omitted if the server is not authenticating with a certificate.
Note that if raw public keys [RFC7250] or the cached information Note that if raw public keys [RFC7250] or the cached information
extension [RFC7924] are in use, then this message will not contain extension [RFC7924] are in use, then this message will not contain
a certificate but rather some other value corresponding to the a certificate but rather some other value corresponding to the
server's long-term key. [Section 4.3.1] server's long-term key. [Section 4.4.1]
CertificateVerify. a signature over the entire handshake using the CertificateVerify. a signature over the entire handshake using the
public key in the Certificate message. This message is omitted if public key in the Certificate message. This message is omitted if
the server is not authenticating via a certificate. the server is not authenticating via a certificate.
[Section 4.3.2] [Section 4.4.2]
Finished. a MAC (Message Authentication Code) over the entire Finished. a MAC (Message Authentication Code) over the entire
handshake. This message provides key confirmation, binds the handshake. This message provides key confirmation, binds the
endpoint's identity to the exchanged keys, and in PSK mode also endpoint's identity to the exchanged keys, and in PSK mode also
authenticates the handshake. [Section 4.3.3] authenticates the handshake. [Section 4.4.3]
Upon receiving the server's messages, the client responds with its Upon receiving the server's messages, the client responds with its
Authentication messages, namely Certificate and CertificateVerify (if Authentication messages, namely Certificate and CertificateVerify (if
requested), and Finished. requested), and Finished.
At this point, the handshake is complete, and the client and server At this point, the handshake is complete, and the client and server
may exchange application layer data. Application data MUST NOT be may exchange application layer data. Application data MUST NOT be
sent prior to sending the Finished message. Note that while the sent prior to sending the Finished message. Note that while the
server may send application data prior to receiving the client's server may send application data prior to receiving the client's
Authentication messages, any data sent at that point is, of course, Authentication messages, any data sent at that point is, of course,
being sent to an unauthenticated peer. being sent to an unauthenticated peer.
2.1. Incorrect DHE Share 2.1. Incorrect DHE Share
If the client has not provided a sufficient "key_share" extension If the client has not provided a sufficient "key_share" extension
(e.g. it includes only DHE or ECDHE groups unacceptable or (e.g., it includes only DHE or ECDHE groups unacceptable or
unsupported by the server), the server corrects the mismatch with a unsupported by the server), the server corrects the mismatch with a
HelloRetryRequest and the client will need to restart the handshake HelloRetryRequest and the client needs to restart the handshake with
with an appropriate "key_share" extension, as shown in Figure 2. If an appropriate "key_share" extension, as shown in Figure 2. If no
no common cryptographic parameters can be negotiated, the server will common cryptographic parameters can be negotiated, the server MUST
send a "handshake_failure" or "insufficient_security" fatal alert abort the handshake with an appropriate alert.
(see Section 6).
Client Server Client Server
ClientHello ClientHello
+ key_share --------> + key_share -------->
<-------- HelloRetryRequest <-------- HelloRetryRequest
ClientHello ClientHello
+ key_share --------> + key_share -------->
ServerHello ServerHello
skipping to change at page 15, line 40 skipping to change at page 16, line 40
HelloRetryRequest exchange; it is not reset with the new ClientHello. HelloRetryRequest exchange; it is not reset with the new ClientHello.
TLS also allows several optimized variants of the basic handshake, as TLS also allows several optimized variants of the basic handshake, as
described in the following sections. described in the following sections.
2.2. Resumption and Pre-Shared Key (PSK) 2.2. Resumption and Pre-Shared Key (PSK)
Although TLS PSKs can be established out of band, PSKs can also be Although TLS PSKs can be established out of band, PSKs can also be
established in a previous session and then reused ("session established in a previous session and then reused ("session
resumption"). Once a handshake has completed, the server can send resumption"). Once a handshake has completed, the server can send
the client a PSK identity which corresponds to a key derived from the the client a PSK identity that corresponds to a key derived from the
initial handshake (See Section 4.4.1). The client can then use that initial handshake (see Section 4.5.1). The client can then use that
PSK identity in future handshakes to negotiate use of the PSK. If PSK identity in future handshakes to negotiate use of the PSK. If
the server accepts it, then the security context of the new the server accepts it, then the security context of the new
connection is tied to the original connection. In TLS 1.2 and below, connection is tied to the original connection. In TLS 1.2 and below,
this functionality was provided by "session IDs" and "session this functionality was provided by "session IDs" and "session
tickets" [RFC5077]. Both mechanisms are obsoleted in TLS 1.3. tickets" [RFC5077]. Both mechanisms are obsoleted in TLS 1.3.
PSKs can be used with (EC)DHE exchange in order to provide forward PSKs can be used with (EC)DHE exchange in order to provide forward
secrecy in combination with shared keys, or can be used alone, at the secrecy in combination with shared keys, or can be used alone, at the
cost of losing forward secrecy. cost of losing forward secrecy.
skipping to change at page 16, line 43 skipping to change at page 17, line 43
+ key_share* + key_share*
{EncryptedExtensions} {EncryptedExtensions}
{Finished} {Finished}
<-------- [Application Data*] <-------- [Application Data*]
{Finished} --------> {Finished} -------->
[Application Data] <-------> [Application Data] [Application Data] <-------> [Application Data]
Figure 3: Message flow for resumption and PSK Figure 3: Message flow for resumption and PSK
As the server is authenticating via a PSK, it does not send a As the server is authenticating via a PSK, it does not send a
Certificate or a CertificateVerify. When a client offers resumption Certificate or a CertificateVerify message. When a client offers
via PSK it SHOULD also supply a "key_share" extension to the server resumption via PSK, it SHOULD also supply a "key_share" extension to
as well to allow the server to decline resumption and fall back to a the server as well to allow the server to decline resumption and fall
full handshake, if needed. The server responds with a back to a full handshake, if needed. The server responds with a
"pre_shared_key" extension to negotiate use of PSK key establishment "pre_shared_key" extension to negotiate use of PSK key establishment
and can (as shown here) respond with a "key_share" extension to do and can (as shown here) respond with a "key_share" extension to do
(EC)DHE key establishment, thus providing forward secrecy. (EC)DHE key establishment, thus providing forward secrecy.
2.3. Zero-RTT Data 2.3. Zero-RTT Data
When resuming via a PSK with an appropriate ticket (i.e., one with When resuming via a PSK with an appropriate ticket (i.e., one with
the "allow_early_data" flag), clients can also send data on their the "early_data_info" extension), clients can also send data on their
first flight ("early data"). This data is encrypted solely under first flight ("early data"). This data is encrypted solely under
keys derived using the first offered PSK as the static secret. As keys derived using the first offered PSK as the static secret. As
shown in Figure 4, the Zero-RTT data is just added to the 1-RTT shown in Figure 4, the Zero-RTT data is just added to the 1-RTT
handshake in the first flight. The rest of the handshake uses the handshake in the first flight. The rest of the handshake uses the
same messages. same messages as with a 1-RTT handshake with PSK resumption.
Client Server Client Server
ClientHello ClientHello
+ early_data + early_data
+ pre_shared_key + pre_shared_key
+ key_share* + key_share*
(Finished) (Finished)
(Application Data*) (Application Data*)
(end_of_early_data) --------> (end_of_early_data) -------->
ServerHello ServerHello
+ early_data + early_data
+ pre_shared_key + pre_shared_key
+ key_share* + key_share*
{EncryptedExtensions} {EncryptedExtensions}
{CertificateRequest*}
{Finished} {Finished}
<-------- [Application Data*] <-------- [Application Data*]
{Certificate*}
{CertificateVerify*}
{Finished} --------> {Finished} -------->
[Application Data] <-------> [Application Data] [Application Data] <-------> [Application Data]
* Indicates optional or situation-dependent * Indicates optional or situation-dependent
messages that are not always sent. messages that are not always sent.
() Indicates messages protected using keys () Indicates messages protected using keys
derived from early_traffic_secret. derived from client_early_traffic_secret.
{} Indicates messages protected using keys {} Indicates messages protected using keys
derived from handshake_traffic_secret. derived from handshake_traffic_secret.
[] Indicates messages protected using keys [] Indicates messages protected using keys
derived from traffic_secret_N derived from traffic_secret_N
Figure 4: Message flow for a zero round trip handshake Figure 4: Message flow for a zero round trip handshake
[[OPEN ISSUE: Should it be possible to combine 0-RTT with the server [[OPEN ISSUE: Should it be possible to combine 0-RTT with the server
skipping to change at page 18, line 19 skipping to change at page 19, line 14
IMPORTANT NOTE: The security properties for 0-RTT data are weaker IMPORTANT NOTE: The security properties for 0-RTT data are weaker
than those for other kinds of TLS data. Specifically: than those for other kinds of TLS data. Specifically:
1. This data is not forward secret, because it is encrypted solely 1. This data is not forward secret, because it is encrypted solely
with the PSK. with the PSK.
2. There are no guarantees of non-replay between connections. 2. There are no guarantees of non-replay between connections.
Unless the server takes special measures outside those provided Unless the server takes special measures outside those provided
by TLS, the server has no guarantee that the same 0-RTT data was by TLS, the server has no guarantee that the same 0-RTT data was
not transmitted on multiple 0-RTT connections (See not transmitted on multiple 0-RTT connections (See
Section 4.2.6.2 for more details). This is especially relevant Section 4.2.7.2 for more details). This is especially relevant
if the data is authenticated either with TLS client if the data is authenticated either with TLS client
authentication or inside the application layer protocol. authentication or inside the application layer protocol.
However, 0-RTT data cannot be duplicated within a connection However, 0-RTT data cannot be duplicated within a connection
(i.e., the server will not process the same data twice for the (i.e., the server will not process the same data twice for the
same connection) and an attacker will not be able to make 0-RTT same connection) and an attacker will not be able to make 0-RTT
data appear to be 1-RTT data (because it is protected with data appear to be 1-RTT data (because it is protected with
different keys.) different keys.)
The remainder of this document provides a detailed description of The remainder of this document provides a detailed description of
TLS. TLS.
skipping to change at page 20, line 8 skipping to change at page 21, line 5
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 actual length field consumes two bytes, a uint16, which is The actual length field consumes two bytes, a uint16, which is
sufficient to represent the value 400 (see Section 3.4). On the sufficient to represent the value 400 (see Section 3.4). On the
other hand, longer can represent up to 800 bytes of data, or 400 other hand, longer can represent up to 800 bytes of data, or 400
uint16 elements, and it may be empty. Its encoding will include a uint16 elements, and it may be empty. Its encoding will include a
two-byte actual length field prepended to the vector. The length of two-byte actual length field prepended to the vector. The length of
an encoded vector must be an even multiple of the length of a single an encoded vector must be an exact multiple of the length of a single
element (for example, a 17-byte vector of uint16 would be illegal). element (e.g., a 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 */
3.4. Numbers 3.4. 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
skipping to change at page 20, line 32 skipping to change at page 21, line 29
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 byte (big-endian) order; the uint32 represented by the hex network byte (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., additional leading zero
octets are not used even if the most significant bit is set).
3.5. Enumerateds 3.5. 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 be assigned a value, as demonstrated in the following example. must be assigned a value, as demonstrated in the following example.
Since the elements of the enumerated are not ordered, they can be Since the elements of the enumerated are not ordered, they can be
assigned any unique value, in any order. assigned any unique value, in any order.
skipping to change at page 22, line 7 skipping to change at page 22, line 48
3.6.1. Variants 3.6.1. 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. Case arms have limited fall-through: if two case arms the select. Case arms have limited fall-through: if two case arms
follow in immediate succession with no fields in between, then they follow in immediate succession with no fields in between, then they
both contain the same fields. Thus, in the example below, "orange" both contain the same fields. Thus, in the example below, "orange"
and "banana" both contain V2. Note that this is a new piece of and "banana" both contain V2. Note that this piece of syntax was
syntax in TLS 1.2. added in TLS 1.2 [RFC5246].
The body of the variant structure may be given a label for reference. The body of the variant structure may be given a label for reference.
The mechanism by which the variant is selected at runtime is not The mechanism by which the variant is selected at runtime is not
prescribed by the presentation language. prescribed by the presentation language.
struct { struct {
T1 f1; T1 f1;
T2 f2; T2 f2;
.... ....
Tn fn; Tn fn;
select (E) { select (E) {
case e1: Te1; case e1: Te1;
case e2: Te2; case e2: Te2;
case e3: case e4: Te3; case e3: case e4: Te3;
.... ....
case en: Ten; case en: Ten;
} [[fv]]; } [[fv]];
} [[Tv]]; } [[Tv]];
For example: For example:
enum { apple, orange, banana } VariantTag; enum { apple, orange, banana } VariantTag;
struct { struct {
uint16 number; uint16 number;
opaque string<0..10>; /* variable length */ opaque string<0..10>; /* variable length */
} V1; } V1;
skipping to change at page 23, line 12 skipping to change at page 24, line 7
} variant_body; /* optional label on variant */ } variant_body; /* optional label on variant */
} VariantRecord; } VariantRecord;
3.7. Constants 3.7. 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 omitted.
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 */
3.8. Decoding Errors
TLS defines two generic alerts (see Section 6) to use upon failure to
parse a message. Peers which receive a message which cannot be
parsed according to the syntax (e.g., have a length extending beyond
the message boundary or contain an out-of-range length) MUST
terminate the connection with a "decoding_error" alert. Peers which
receive a message which is syntactically correct but semantically
invalid (e.g., a DHE share of p - 1) MUST terminate the connection
with an "illegal_parameter" alert.
4. Handshake Protocol 4. Handshake Protocol
The handshake protocol is used to negotiate the secure attributes of The handshake protocol is used to negotiate the secure attributes of
a session. Handshake messages are supplied to the TLS record layer, a session. Handshake messages are supplied to the TLS record layer,
where they are encapsulated within one or more TLSPlaintext or where they are encapsulated within one or more TLSPlaintext or
TLSCiphertext structures, which are processed and transmitted as TLSCiphertext structures, which are processed and transmitted as
specified by the current active session state. specified by the current active session state.
enum { enum {
client_hello(1), client_hello(1),
skipping to change at page 24, line 22 skipping to change at page 25, line 22
certificate_request(13), certificate_request(13),
certificate_verify(15), certificate_verify(15),
finished(20), finished(20),
key_update(24), key_update(24),
(255) (255)
} HandshakeType; } HandshakeType;
struct { struct {
HandshakeType msg_type; /* handshake type */ HandshakeType msg_type; /* handshake type */
uint24 length; /* bytes in message */ uint24 length; /* bytes in message */
select (HandshakeType) { select (Handshake.msg_type) {
case client_hello: ClientHello; case client_hello: ClientHello;
case server_hello: ServerHello; case server_hello: ServerHello;
case hello_retry_request: HelloRetryRequest; case hello_retry_request: HelloRetryRequest;
case encrypted_extensions: EncryptedExtensions; case encrypted_extensions: EncryptedExtensions;
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case certificate: Certificate; case certificate: Certificate;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case finished: Finished; case finished: Finished;
case new_session_ticket: NewSessionTicket; case new_session_ticket: NewSessionTicket;
case key_update: KeyUpdate; case key_update: KeyUpdate;
} body; } body;
} Handshake; } Handshake;
Protocol messages MUST be sent in the order defined below (and shown Protocol messages MUST be sent in the order defined below (and shown
in the diagrams in Section 2). Sending handshake messages in an in the diagrams in Section 2). A peer which receives a handshake
unexpected order results in an "unexpected_message" fatal error. message in an unexpected order MUST abort the handshake with an
Unneeded handshake messages are omitted, however. "unexpected_message" alert. results in an "unexpected_message" fatal
error. Unneeded handshake messages are omitted, however.
New handshake message types are assigned by IANA as described in New handshake message types are assigned by IANA as described in
Section 10. Section 10.
4.1. Key Exchange Messages 4.1. Key Exchange Messages
The key exchange messages are used to exchange security capabilities The key exchange messages are used to exchange security capabilities
between the client and server and to establish the traffic keys used between the client and server and to establish the traffic keys used
to protect the handshake and data. to protect the handshake and data.
4.1.1. Cryptographic Negotiation 4.1.1. Cryptographic Negotiation
TLS cryptographic negotiation proceeds by the client offering the TLS cryptographic negotiation proceeds by the client offering the
following four sets of options in its ClientHello. following four sets of options in its ClientHello:
- A list of cipher suites which indicates the AEAD cipher/HKDF hash - A list of cipher suites which indicates the AEAD algorithm/HKDF
pairs which the client supports hash pairs which the client supports.
- A "supported_group" (Section 4.2.3) extension which indicates the - A "supported_group" (Section 4.2.4) extension which indicates the
(EC)DHE groups which the client supports and a "key_share" (EC)DHE groups which the client supports and a "key_share"
(Section 4.2.4) extension which contains (EC)DHE shares for some (Section 4.2.5) extension which contains (EC)DHE shares for some
or all of these groups or all of these groups.
- A "signature_algorithms" (Section 4.2.2) extension which indicates - A "signature_algorithms" (Section 4.2.3) extension which indicates
the signature algorithms which the client can accept. the signature algorithms which the client can accept.
- A "pre_shared_key" (Section 4.2.5) extension which contains the - A "pre_shared_key" (Section 4.2.6) extension which contains the
identities of symmetric keys known to the client and the key identities of symmetric keys known to the client and the key
exchange modes which each PSK supports. exchange modes which each PSK supports.
If the server does not select a PSK, then the first three of these If the server does not select a PSK, then the first three of these
options are entirely orthogonal: the server independently selects a options are entirely orthogonal: the server independently selects a
cipher suite, an (EC)DHE group and key share for key establishment, cipher suite, an (EC)DHE group and key share for key establishment,
and a signature algorithm/certificate pair to authenticate itself to and a signature algorithm/certificate pair to authenticate itself to
the client. If any of these parameters has no overlap between the the client. If there is overlap in the "supported_group" extension
client and server parameters, then the handshake will fail. If there but the client did not offer a compatible "key_share" extension, then
is overlap in the "supported_group" extension but the client did not the server will respond with a HelloRetryRequest (Section 4.1.4)
offer a compatible "key_share" extension, then the server will message.
respond with a HelloRetryRequest (Section 4.1.4) message.
If the server selects a PSK, then the PSK will indicate which key If the server selects a PSK, then the PSK will indicate which key
establishment modes it can be used with (PSK alone or with (EC)DHE) establishment modes it can be used with (PSK alone or with (EC)DHE)
and which authentication modes it can be used with (PSK alone or PSK and which authentication modes it can be used with (PSK alone or PSK
with signatures). The server can then select those key establishment with signatures). The server can then select those key establishment
and authentication parameters to be consistent both with the PSK and and authentication parameters to be consistent both with the PSK and
the other extensions supplied by the client. Note that if the PSK the other extensions supplied by the client. Note that if the PSK
can be used without (EC)DHE or without signatures, then non-overlap can be used without (EC)DHE or without signatures, then non-overlap
in either of these parameters need not be fatal. in either of these parameters need not be fatal.
The server indicates its selected parameters in the ServerHello as The server indicates its selected parameters in the ServerHello as
follows: If PSK is being used then the server will send a follows:
"pre_shared_key" extension indicating the selected key. If PSK is
not being used, then (EC)DHE and certificate-based authentication are
always used. When (EC)DHE is in use, the server will also provide a
"key_share" extension. When authenticating via a certificate, the
server will send an empty "signature_algorithnms" extension in the
ServerHello and will subsequently send Certificate (Section 4.3.1)
and CertificateVerify (Section 4.3.2) messages.
If the server is unable to negotiate a supported set of parameters, - If PSK is being used then the server will send a "pre_shared_key"
it MUST return a "handshake_failure" alert and close the connection. extension indicating the selected key.
- If PSK is not being used, then (EC)DHE and certificate-based
authentication are always used.
- When (EC)DHE is in use, the server will also provide a "key_share"
extension.
- When authenticating via a certificate, the server will send an
empty "signature_algorithms" extension in the ServerHello and will
subsequently send Certificate (Section 4.4.1) and
CertificateVerify (Section 4.4.2) messages.
If the server is unable to negotiate a supported set of parameters
(i.e., there is no overlap between the client and server parameters),
it MUST abort the handshake and and SHOULD send either a
"handshake_failure" or "insufficient_security" fatal alert (see
Section 6).
4.1.2. Client Hello 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 ClientHello as its first message. The client will also send a the ClientHello as its first message. The client will also send a
ClientHello when the server has responded to its ClientHello with ClientHello when the server has responded to its ClientHello with
a HelloRetryRequest that selects cryptographic parameters that a HelloRetryRequest. In that case, the client MUST send the same
don't match the client's "key_share" extension. In that case, the ClientHello (without modification) except:
client MUST send the same ClientHello (without modification)
except:
- Including a new KeyShareEntry as the lowest priority share (i.e., - Including a new KeyShareEntry as the lowest priority share (i.e.,
appended to the list of shares in the "key_share" extension). appended to the list of shares in the "key_share" extension).
- Removing the EarlyDataIndication Section 4.2.6 extension if one - Removing the "early_data" extension (Section 4.2.7) if one was
was present. Early data is not permitted after HelloRetryRequest. present. Early data is not permitted after HelloRetryRequest.
If a server receives a ClientHello at any other time, it MUST send a - Including a "cookie" extension if one was provided in the
fatal "unexpected_message" alert and close the connection. HelloRetryRequest.
Because TLS 1.3 forbids renegotiation, if a server receives a
ClientHello at any other time, it MUST terminate the connection.
If a server established a TLS connection with a previous version of
TLS and receives a TLS 1.3 ClientHello in a renegotiation, it MUST
retain the previous protocol version. In particular, it MUST NOT
negotiate TLS 1.3. A client that receives a TLS 1.3 ServerHello
during renegotiation MUST abort the handshake with a
"protocol_version" alert.
Structure of this message: Structure of this message:
struct { struct {
uint8 major; uint8 major;
uint8 minor; uint8 minor;
} ProtocolVersion; } ProtocolVersion;
struct { struct {
opaque random_bytes[32]; opaque random_bytes[32];
} Random; } Random;
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
struct { struct {
ProtocolVersion max_supported_version = { 3, 4 }; /* TLS v1.3 */ ProtocolVersion legacy_version = { 3, 3 }; /* TLS v1.2 */
Random random; Random random;
opaque legacy_session_id<0..32>; opaque legacy_session_id<0..32>;
CipherSuite cipher_suites<2..2^16-2>; CipherSuite cipher_suites<2..2^16-2>;
opaque legacy_compression_methods<1..2^8-1>; opaque legacy_compression_methods<1..2^8-1>;
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} ClientHello; } ClientHello;
TLS allows extensions to follow the compression_methods field in an TLS allows extensions to follow the compression_methods field in an
extensions block. The presence of extensions can be detected by extensions block. The presence of extensions can be detected by
determining whether there are bytes following the compression_methods determining whether there are bytes following the compression_methods
at the end of the ClientHello. Note that this method of detecting at the end of the ClientHello. Note that this method of detecting
optional data differs from the normal TLS method of having a optional data differs from the normal TLS method of having a
variable-length field, but it is used for compatibility with TLS variable-length field, but it is used for compatibility with TLS
before extensions were defined. As of TLS 1.3, all clients and before extensions were defined. As of TLS 1.3, all clients and
servers will send at least one extension (at least "key_share" or servers will send at least one extension (at least "key_share" or
"pre_shared_key"). "pre_shared_key").
max_supported_version The latest (highest valued) version of the TLS legacy_version In previous versions of TLS, this field was used for
protocol offered by the client. This SHOULD be the same as the version negotiation and represented the highest version number
latest version supported. For this version of the specification, supported by the client. Experience has shown that many servers
the version will be { 3, 4 }. (See Appendix C for details about do not properly implement version negotiation, leading to "version
backward compatibility.) intolerance" in which the server rejects an otherwise acceptable
ClientHello with a version number higher than it supports.
In TLS 1.3, the client indicates its version preferences in the
"suported_versions" extension (Section 4.2.1) and this field MUST
be set to {3, 3}, which was the version number for TLS 1.2. (See
Appendix C for details about backward compatibility.)
random 32 bytes generated by a secure random number generator. See random 32 bytes generated by a secure random number generator. See
Appendix B for additional information. Appendix B for additional information.
legacy_session_id Versions of TLS before TLS 1.3 supported a session legacy_session_id Versions of TLS before TLS 1.3 supported a session
resumption feature which has been merged with Pre-Shared Keys in resumption feature which has been merged with Pre-Shared Keys in
this version (see Section 2.2). This field MUST be ignored by a this version (see Section 2.2). This field MUST be ignored by a
server negotiating TLS 1.3 and SHOULD be set as a zero length server negotiating TLS 1.3 and SHOULD be set as a zero length
vector (i.e., a single zero byte length field) by clients which do vector (i.e., a single zero byte length field) by clients which do
not have a cached session ID set by a pre-TLS 1.3 server. not have a cached session ID set by a pre-TLS 1.3 server.
skipping to change at page 27, line 43 skipping to change at page 29, line 22
wish to use, the server MUST ignore those cipher suites, and wish to use, the server MUST ignore those cipher suites, and
process the remaining ones as usual. Values are defined in process the remaining ones as usual. Values are defined in
Appendix A.4. Appendix A.4.
legacy_compression_methods Versions of TLS before 1.3 supported legacy_compression_methods Versions of TLS before 1.3 supported
compression with the list of supported compression methods being compression with the list of supported compression methods being
sent in this field. For every TLS 1.3 ClientHello, this vector sent in this field. For every TLS 1.3 ClientHello, this vector
MUST contain exactly one byte set to zero, which corresponds to MUST contain exactly one byte set to zero, which corresponds to
the "null" compression method in prior versions of TLS. If a TLS the "null" compression method in prior versions of TLS. If a TLS
1.3 ClientHello is received with any other value in this field, 1.3 ClientHello is received with any other value in this field,
the server MUST generate a fatal "illegal_parameter" alert. Note the server MUST abort the handshake with an "illegal_parameter"
that TLS 1.3 servers might receive TLS 1.2 or prior ClientHellos alert. Note that TLS 1.3 servers might receive TLS 1.2 or prior
which contain other compression methods and MUST follow the ClientHellos which contain other compression methods and MUST
procedures for the appropriate prior version of TLS. follow the procedures for the appropriate prior version of TLS.
extensions Clients request extended functionality from servers by extensions Clients request extended functionality from servers by
sending data in the extensions field. The actual "Extension" sending data in the extensions field. The actual "Extension"
format is defined in Section 4.2. format is defined in Section 4.2.
In the event that a client requests additional functionality using In the event that a client requests additional functionality using
extensions, and this functionality is not supplied by the server, the extensions, and this functionality is not supplied by the server, the
client MAY abort the handshake. Note that TLS 1.3 ClientHello client MAY abort the handshake. Note that TLS 1.3 ClientHello
messages MUST always contain extensions, and a TLS 1.3 server MUST messages MUST always contain extensions, and a TLS 1.3 server MUST
respond to any TLS 1.3 ClientHello without extensions with a fatal respond to any TLS 1.3 ClientHello without extensions or with data
"decode_error" alert. TLS 1.3 servers may receive TLS 1.2 following the extensions block with a "decode_error" alert. TLS 1.3
ClientHello messages without extensions. If negotiating TLS 1.2, a servers may receive TLS 1.2 ClientHello messages without extensions.
server MUST check that the amount of data in the message precisely If negotiating TLS 1.2, a server MUST check that the message either
matches one of these formats; if not, then it MUST send a fatal contains no data after legacy_compression_methods or that it contains
"decode_error" alert. a valid extensions block with no data following. If not, then it
MUST abort the handshake with a "decode_error" alert.
After sending the ClientHello message, the client waits for a After sending the ClientHello message, the client waits for a
ServerHello or HelloRetryRequest message. ServerHello or HelloRetryRequest message.
4.1.3. Server Hello 4.1.3. Server Hello
When this message will be sent: When this message will be sent:
The server will send this message in response to a ClientHello The server will send this message in response to a ClientHello
message when it was able to find an acceptable set of algorithms message when it was able to find an acceptable set of algorithms
skipping to change at page 28, line 51 skipping to change at page 30, line 30
ClientHello. In particular, servers MUST accept ClientHello ClientHello. In particular, servers MUST accept ClientHello
messages with versions higher than those supported and negotiate messages with versions higher than those supported and negotiate
the highest mutually supported version. For this version of the the highest mutually supported version. For this version of the
specification, the version is { 3, 4 }. (See Appendix C for specification, the version is { 3, 4 }. (See Appendix C for
details about backward compatibility.) details about backward compatibility.)
random This structure is generated by the server and MUST be random This structure is generated by the server and MUST be
generated independently of the ClientHello.random. generated independently of the ClientHello.random.
cipher_suite The single cipher suite selected by the server from the cipher_suite The single cipher suite selected by the server from the
list in ClientHello.cipher_suites. list in ClientHello.cipher_suites. A client which receives a
cipher suite that was not offered MUST abort the handshake.
extensions A list of extensions. Note that only extensions offered extensions A list of extensions. Note that only extensions offered
by the client can appear in the server's list. In TLS 1.3, as by the client can appear in the server's list. In TLS 1.3, as
opposed to previous versions of TLS, the server's extensions are opposed to previous versions of TLS, the server's extensions are
split between the ServerHello and the EncryptedExtensions split between the ServerHello and the EncryptedExtensions
Section 4.2.8 message. The ServerHello MUST only include Section 4.3.1 message. The ServerHello MUST only include
extensions which are required to establish the cryptographic extensions which are required to establish the cryptographic
context. Currently the only such extensions are "key_share", context. Currently the only such extensions are "key_share",
"pre_shared_key", and "early_data". Clients MUST check the "pre_shared_key", and "signature_algorithms". Clients MUST check
ServerHello for the presence of any forbidden extensions and if the ServerHello for the presence of any forbidden extensions and
any are found MUST terminate the handshake with a if any are found MUST abort the handshake with a
"illegal_parameter" alert. In prior versions of TLS, the "illegal_parameter" alert. In prior versions of TLS, the
extensions field could be omitted entirely if not needed, similar extensions field could be omitted entirely if not needed, similar
to ClientHello. As of TLS 1.3, all clients and servers will send to ClientHello. As of TLS 1.3, all clients and servers will send
at least one extension (at least "key_share" or "pre_shared_key"). at least one extension (at least "key_share" or "pre_shared_key").
TLS 1.3 has a downgrade protection mechanism embedded in the server's TLS 1.3 has a downgrade protection mechanism embedded in the server's
random value. TLS 1.3 server implementations which respond to a random value. TLS 1.3 server implementations which respond to a
ClientHello with a max_supported_version indicating TLS 1.2 or below ClientHello indicating only support for TLS 1.2 or below MUST set the
MUST set the last eight bytes of their Random value to the bytes: last eight bytes of their Random value to the bytes:
44 4F 57 4E 47 52 44 01 44 4F 57 4E 47 52 44 01
TLS 1.2 server implementations which respond to a ClientHello with a TLS 1.3 server implementations which respond to a ClientHello
max_supported_version indicating TLS 1.1 or below SHOULD set the last indicating only support for TLS 1.1 or below SHOULD set the last
eight bytes of their Random value to the bytes: eight bytes of their Random value to the bytes:
44 4F 57 4E 47 52 44 00 44 4F 57 4E 47 52 44 00
TLS 1.3 clients receiving a TLS 1.2 or below ServerHello MUST check TLS 1.3 clients receiving a TLS 1.2 or below ServerHello MUST check
that the last eight octets are not equal to either of these values. that the last eight octets are not equal to either of these values.
TLS 1.2 clients SHOULD also perform this check if the ServerHello TLS 1.2 clients SHOULD also perform this check if the ServerHello
indicates TLS 1.1 or below. If a match is found, the client MUST indicates TLS 1.1 or below. If a match is found, the client MUST
abort the handshake with a fatal "illegal_parameter" alert. This abort the handshake with an "illegal_parameter" alert. This
mechanism provides limited protection against downgrade attacks over mechanism provides limited protection against downgrade attacks over
and above that provided by the Finished exchange: because the and above that provided by the Finished exchange: because the
ServerKeyExchange includes a signature over both random values, it is ServerKeyExchange includes a signature over both random values, it is
not possible for an active attacker to modify the randoms without not possible for an active attacker to modify the randoms without
detection as long as ephemeral ciphers are used. It does not provide detection as long as ephemeral ciphers are used. It does not provide
downgrade protection when static RSA is used. downgrade protection when static RSA is used.
Note: This is an update to TLS 1.2 so in practice many TLS 1.2 Note: This is an update to TLS 1.2 so in practice many TLS 1.2
clients and servers will not behave as specified above. clients and servers will not behave as specified above.
RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH Implementations of
draft versions (see Section 4.2.1.1) of this specification SHOULD NOT
implement this mechanism on either client and server. A pre-RFC
client connecting to RFC servers, or vice versa, will appear to
downgrade to TLS 1.2. With the mechanism enabled, this will cause an
interoperability failure.
4.1.4. Hello Retry Request 4.1.4. Hello Retry Request
When this message will be sent: When this message will be sent:
Servers send this message in response to a ClientHello message if Servers send this message in response to a ClientHello message if
they were able to find an acceptable set of algorithms and groups they were able to find an acceptable set of algorithms and groups
that are mutually supported, but the client's KeyShare did not that are mutually supported, but the client's ClientHello did not
contain an acceptable offer. If it cannot find such a match, it contain sufficient information to proceed with the handshake. If
will respond with a fatal "handshake_failure" alert. a server cannot successfully select algorithms, it MUST abort the
handshake with a "handshake_failure" alert.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
NamedGroup selected_group; Extension extensions<2..2^16-1>;
Extension extensions<0..2^16-1>;
} HelloRetryRequest; } HelloRetryRequest;
selected_group The mutually supported group the server intends to
negotiate and is requesting a retried ClientHello/KeyShare for.
The version and extensions fields have the same meanings as their The version and extensions fields have the same meanings as their
corresponding values in the ServerHello. The server SHOULD send only corresponding values in the ServerHello. The server SHOULD send only
the extensions necessary for the client to generate a correct the extensions necessary for the client to generate a correct
ClientHello pair (currently no such extensions exist). As with ClientHello pair (currently no such extensions exist). As with
ServerHello, a HelloRetryRequest MUST NOT contain any extensions that ServerHello, a HelloRetryRequest MUST NOT contain any extensions that
were not first offered by the client in its ClientHello. were not first offered by the client in its ClientHello, with the
exception of optionally the "cookie" (see Section 4.2.2) extension.
Upon receipt of a HelloRetryRequest, the client MUST first verify Upon receipt of a HelloRetryRequest, the client MUST verify that the
that the selected_group field corresponds to a group which was extensions block is not empty and otherwise MUST abort the handshake
provided in the "supported_groups" extension in the original with a "decode_error" alert. Clients SHOULD also abort the handshake
ClientHello. It MUST then verify that the selected_group field does with an "unexpected_message" alert in response to any second
not correspond to a group which was provided in the "key_share" HelloRetryRequest which was sent in the same connection (i.e., where
extension in the original ClientHello. If either of these checks the ClientHello was itself in response to a HelloRetryRequest).
fails, then the client MUST abort the handshake with a fatal
"illegal_parameter" alert. Clients SHOULD also abort with
"unexpected_message" in response to any second HelloRetryRequest
which was sent in the same connection (i.e., where the ClientHello
was itself in response to a HelloRetryRequest).
Otherwise, the client MUST send a ClientHello with an updated Otherwise, the client MUST process all extensions in the
KeyShare extension to the server. The client MUST append a new HelloRetryRequest and send a second updated ClientHello. The
KeyShareEntry for the group indicated in the selected_group field to HelloRetryRequest extensions defined in this specification are:
the groups in its original KeyShare.
Upon re-sending the ClientHello and receiving the server's - cookie (see Section 4.2.2)
ServerHello/KeyShare, the client MUST verify that the selected
NamedGroup matches that supplied in the HelloRetryRequest and MUST - key_share (see Section 4.2.5)
abort the connection with a fatal "illegal_parameter" alert if it
does not. Note that HelloRetryRequest extensions are defined such that the
original ClientHello may be computed from the new one, given minimal
state about which HelloRetryRequest extensions were sent. For
example, the key_share extension causes the new KeyShareEntry to be
appended to the client_shares field, rather than replacing it.
4.2. Hello Extensions 4.2. Hello Extensions
The extension format is: The extension format is:
struct { struct {
ExtensionType extension_type; ExtensionType extension_type;
opaque extension_data<0..2^16-1>; opaque extension_data<0..2^16-1>;
} Extension; } Extension;
enum { enum {
supported_groups(10), supported_groups(10),
signature_algorithms(13), signature_algorithms(13),
key_share(40), key_share(40),
pre_shared_key(41), pre_shared_key(41),
early_data(42), early_data(42),
supported_versions(43),
cookie(44), cookie(44),
(65535) (65535)
} ExtensionType; } ExtensionType;
Here: Here:
- "extension_type" identifies the particular extension type. - "extension_type" identifies the particular extension type.
- "extension_data" contains information specific to the particular - "extension_data" contains information specific to the particular
extension type. extension type.
skipping to change at page 32, line 43 skipping to change at page 34, line 22
manipulation of handshake messages. This principle should be manipulation of handshake messages. This principle should be
followed regardless of whether the feature is believed to cause a followed regardless of whether the feature is believed to cause a
security problem. Often the fact that the extension fields are security problem. Often the fact that the extension fields are
included in the inputs to the Finished message hashes will be included in the inputs to the Finished message hashes will be
sufficient, but extreme care is needed when the extension changes sufficient, but extreme care is needed when the extension changes
the meaning of messages sent in the handshake phase. Designers the meaning of messages sent in the handshake phase. Designers
and implementors should be aware of the fact that until the and implementors should be aware of the fact that until the
handshake has been authenticated, active attackers can modify handshake has been authenticated, active attackers can modify
messages and insert, remove, or replace extensions. messages and insert, remove, or replace extensions.
4.2.1. Cookie 4.2.1. Supported Versions
struct {
ProtocolVersion versions<2..254>;
} SupportedVersions;
The "supported_versions" extension is used by the client to indicate
which versions of TLS it supports. The extension contains a list of
supported versions in preference order, with the most preferred
version first. Implementations of this specification MUST send this
extension containing all versions of TLS which they are prepared to
negotiate (for this specification, that means minimally {3, 4}, but
if previous versions of TLS are supported, they MUST be present as
well).
Servers which are compliant with this specification MUST use only the
"supported_versions" extension, if present, to determine client
preferences and MUST only select a version of TLS present in that
extension. They MUST ignore any unknown versions. If the extension
is not present, they MUST negotiate TLS 1.2 or prior as specified in
[RFC5246], even if ClientHello.legacy_version is {3, 4} or later.
The server MUST NOT send the "supported_versions" extension. The
server's selected version is contained in the ServerHello.version
field as in previous versions of TLS.
4.2.1.1. Draft Version Indicator
RFC EDITOR: PLEASE REMOVE THIS SECTION
While the eventual version indicator for the RFC version of TLS 1.3
will be {3, 4}, implementations of draft versions of this
specification SHOULD instead advertise {0x7f, [draft-version]} in
their "supported_versions" extension, in ServerHello.version, and
HelloRetryRequest.server_version. This allows pre-RFC
implementations to safely negotiate with each other, even if they
would otherwise be incompatible.
4.2.2. Cookie
struct { struct {
opaque cookie<0..2^16-1>; opaque cookie<0..2^16-1>;
} Cookie; } Cookie;
Cookies serve two primary purposes: Cookies serve two primary purposes:
- Allowing the server to force the client to demonstrate - Allowing the server to force the client to demonstrate
reachability at their apparent network address (thus providing a reachability at their apparent network address (thus providing a
measure of DoS protection). This is primarily useful for non- measure of DoS protection). This is primarily useful for non-
skipping to change at page 33, line 20 skipping to change at page 35, line 38
server does this by pickling that post-ClientHello hash state into server does this by pickling that post-ClientHello hash state into
the cookie (protected with some suitable integrity algorithm). the cookie (protected with some suitable integrity algorithm).
When sending a HelloRetryRequest, the server MAY provide a "cookie" When sending a HelloRetryRequest, the server MAY provide a "cookie"
extension to the client (this is an exception to the usual rule that extension to the client (this is an exception to the usual rule that
the only extensions that may be sent are those that appear in the the only extensions that may be sent are those that appear in the
ClientHello). When sending the new ClientHello, the client MUST echo ClientHello). When sending the new ClientHello, the client MUST echo
the value of the extension. Clients MUST NOT use cookies in the value of the extension. Clients MUST NOT use cookies in
subsequent connections. subsequent connections.
4.2.2. Signature Algorithms 4.2.3. Signature Algorithms
The client uses the "signature_algorithms" extension to indicate to The client uses the "signature_algorithms" extension to indicate to
the server which signature algorithms may be used in digital the server which signature algorithms may be used in digital
signatures. Clients which desire the server to authenticate via a signatures. Clients which desire the server to authenticate via a
certificate MUST send this extension. If a server is authenticating certificate MUST send this extension. If a server is authenticating
via a certificate and the client has not sent a via a certificate and the client has not sent a
"signature_algorithms" extension then the server MUST close the "signature_algorithms" extension then the server MUST abort the
connection with a fatal "missing_extension" alert (see Section 8.2). handshake with a "missing_extension" alert (see Section 8.2).
Servers which are authenticating via a certificate MUST indicate so Servers which are authenticating via a certificate MUST indicate so
by sending the client an empty "signature_algorithms" extension. by sending the client an empty "signature_algorithms" extension.
The "extension_data" field of this extension contains a The "extension_data" field of this extension in a ClientHello
"supported_signature_algorithms" value: contains a "supported_signature_algorithms" value:
enum { enum {
/* RSASSA-PKCS1-v1_5 algorithms */ /* RSASSA-PKCS1-v1_5 algorithms */
rsa_pkcs1_sha1 (0x0201), rsa_pkcs1_sha1 (0x0201),
rsa_pkcs1_sha256 (0x0401), rsa_pkcs1_sha256 (0x0401),
rsa_pkcs1_sha384 (0x0501), rsa_pkcs1_sha384 (0x0501),
rsa_pkcs1_sha512 (0x0601), rsa_pkcs1_sha512 (0x0601),
/* ECDSA algorithms */ /* ECDSA algorithms */
ecdsa_secp256r1_sha256 (0x0403), ecdsa_secp256r1_sha256 (0x0403),
ecdsa_secp384r1_sha384 (0x0503), ecdsa_secp384r1_sha384 (0x0503),
ecdsa_secp521r1_sha512 (0x0603), ecdsa_secp521r1_sha512 (0x0603),
/* RSASSA-PSS algorithms */ /* RSASSA-PSS algorithms */
rsa_pss_sha256 (0x0700), rsa_pss_sha256 (0x0804),
rsa_pss_sha384 (0x0701), rsa_pss_sha384 (0x0805),
rsa_pss_sha512 (0x0702), rsa_pss_sha512 (0x0806),
/* EdDSA algorithms */ /* EdDSA algorithms */
ed25519 (0x0703), ed25519 (0x0807),
ed448 (0x0704), ed448 (0x0808),
/* Reserved Code Points */ /* Reserved Code Points */
private_use (0xFE00..0xFFFF), private_use (0xFE00..0xFFFF),
(0xFFFF) (0xFFFF)
} SignatureScheme; } SignatureScheme;
SignatureScheme supported_signature_algorithms<2..2^16-2>; SignatureScheme supported_signature_algorithms<2..2^16-2>;
Note: This enum is named "SignatureScheme" because there is already a Note: This enum is named "SignatureScheme" because there is already a
"SignatureAlgorithm" type in TLS 1.2, which this replaces. We use "SignatureAlgorithm" type in TLS 1.2, which this replaces. We use
the term "signature algorithm" throughout the text. the term "signature algorithm" throughout the text.
Each SignatureScheme value lists a single signature algorithm that Each SignatureScheme value lists a single signature algorithm that
the client is willing to verify. The values are indicated in the client is willing to verify. The values are indicated in
descending order of preference. Note that a signature algorithm descending order of preference. Note that a signature algorithm
takes as input an arbitrary-length message, rather than a digest. takes as input an arbitrary-length message, rather than a digest.
Algorithms which traditionally act on a digest should be defined in Algorithms which traditionally act on a digest should be defined in
TLS to first hash the input with a specified hash function and then TLS to first hash the input with a specified hash algorithm and then
proceed as usual. The code point groups listed above have the proceed as usual. The code point groups listed above have the
following meanings: following meanings:
RSASSA-PKCS1-v1_5 algorithms Indicates a signature algorithm using RSASSA-PKCS1-v1_5 algorithms Indicates a signature algorithm using
RSASSA-PKCS1-v1_5 [RFC3447] with the corresponding hash algorithm RSASSA-PKCS1-v1_5 [RFC3447] with the corresponding hash algorithm
as defined in [SHS]. These values refer solely to signatures as defined in [SHS]. These values refer solely to signatures
which appear in certificates (see Section 4.3.1.1) and are not which appear in certificates (see Section 4.4.1.1) and are not
defined for use in signed TLS handshake messages. defined for use in signed TLS handshake messages.
ECDSA algorithms Indicates a signature algorithm using ECDSA ECDSA algorithms Indicates a signature algorithm using ECDSA
[ECDSA], the corresponding curve as defined in ANSI X9.62 [X962] [ECDSA], the corresponding curve as defined in ANSI X9.62 [X962]
and FIPS 186-4 [DSS], and the corresponding hash algorithm as and FIPS 186-4 [DSS], and the corresponding hash algorithm as
defined in [SHS]. The signature is represented as a DER-encoded defined in [SHS]. The signature is represented as a DER-encoded
[X690] ECDSA-Sig-Value structure. [X690] ECDSA-Sig-Value structure.
RSASSA-PSS algorithms Indicates a signature algorithm using RSASSA- RSASSA-PSS algorithms Indicates a signature algorithm using RSASSA-
PSS [RFC3447] with MGF1. The digest used in the mask generation PSS [RFC3447] with MGF1. The digest used in the mask generation
function and the digest being signed are both the corresponding function and the digest being signed are both the corresponding
hash algorithm as defined in [SHS]. When used in signed TLS hash algorithm as defined in [SHS]. When used in signed TLS
handshake messages, the length of the salt MUST be equal to the handshake messages, the length of the salt MUST be equal to the
length of the digest output. This codepoint is defined for use length of the digest output. This codepoint is defined for use
with TLS 1.2 as well as TLS 1.3. A server uses RSASSA-PSS with TLS 1.2 as well as TLS 1.3.
signatures with RSA cipher suites.
EdDSA algorithms Indicates a signature algorithm using EdDSA as EdDSA algorithms Indicates a signature algorithm using EdDSA as
defined in [I-D.irtf-cfrg-eddsa] or its successors. Note that defined in [I-D.irtf-cfrg-eddsa] or its successors. Note that
these correspond to the "PureEdDSA" algorithms and not the these correspond to the "PureEdDSA" algorithms and not the
"prehash" variants. A server uses EdDSA signatures with ECDSA "prehash" variants.
cipher suites.
rsa_pkcs1_sha1, dsa_sha1, and ecdsa_sha1 SHOULD NOT be offered. rsa_pkcs1_sha1, dsa_sha1, and ecdsa_sha1 SHOULD NOT be offered.
Clients offering these values for backwards compatibility MUST list Clients offering these values for backwards compatibility MUST list
them as the lowest priority (listed after all other algorithms in the them as the lowest priority (listed after all other algorithms in the
supported_signature_algorithms vector). TLS 1.3 servers MUST NOT supported_signature_algorithms vector). TLS 1.3 servers MUST NOT
offer a SHA-1 signed certificate unless no valid certificate chain offer a SHA-1 signed certificate unless no valid certificate chain
can be produced without it (see Section 4.3.1.1). can be produced without it (see Section 4.4.1.1).
The signatures on certificates that are self-signed or certificates The signatures on certificates that are self-signed or certificates
that are trust anchors are not validated since they begin a that are trust anchors are not validated since they begin a
certification path (see [RFC5280], Section 3.2). A certificate that certification path (see [RFC5280], Section 3.2). A certificate that
begins a certification path MAY use a signature algorithm that is not begins a certification path MAY use a signature algorithm that is not
advertised as being supported in the "signature_algorithms" advertised as being supported in the "signature_algorithms"
extension. extension.
Note that TLS 1.2 defines this extension differently. TLS 1.3 Note that TLS 1.2 defines this extension differently. TLS 1.3
implementations willing to negotiate TLS 1.2 MUST behave in implementations willing to negotiate TLS 1.2 MUST behave in
skipping to change at page 36, line 15 skipping to change at page 38, line 15
be used. be used.
- ECDSA signature schemes align with TLS 1.2's ECDSA hash/signature - ECDSA signature schemes align with TLS 1.2's ECDSA hash/signature
pairs. However, the old semantics did not constrain the signing pairs. However, the old semantics did not constrain the signing
curve. If TLS 1.2 is negotiated, implementations MUST be prepared curve. If TLS 1.2 is negotiated, implementations MUST be prepared
to accept a signature that uses any curve that they advertised in to accept a signature that uses any curve that they advertised in
the "supported_groups" extension. the "supported_groups" extension.
- Implementations that advertise support for RSASSA-PSS (which is - Implementations that advertise support for RSASSA-PSS (which is
mandatory in TLS 1.3), MUST be prepared to accept a signature mandatory in TLS 1.3), MUST be prepared to accept a signature
using that scheme even when TLS 1.2 is negotiated. using that scheme even when TLS 1.2 is negotiated. In TLS 1.2,
RSASSA-PSS is used with RSA cipher suites.
4.2.3. Negotiated Groups 4.2.4. Negotiated Groups
When sent by the client, the "supported_groups" extension indicates When sent by the client, the "supported_groups" extension indicates
the named groups which the client supports for key exchange, ordered the named groups which the client supports for key exchange, ordered
from most preferred to least preferred. from most preferred to least preferred.
Note: In versions of TLS prior to TLS 1.3, this extension was named Note: In versions of TLS prior to TLS 1.3, this extension was named
"elliptic_curves" and only contained elliptic curve groups. See "elliptic_curves" and only contained elliptic curve groups. See
[RFC4492] and [I-D.ietf-tls-negotiated-ff-dhe]. This extension was [RFC4492] and [RFC7919]. This extension was also used to negotiate
also used to negotiate ECDSA curves. Signature algorithms are now ECDSA curves. Signature algorithms are now negotiated independently
negotiated independently (see Section 4.2.2). (see Section 4.2.3).
The "extension_data" field of this extension contains a The "extension_data" field of this extension contains a
"NamedGroupList" value: "NamedGroupList" value:
enum { enum {
/* Elliptic Curve Groups (ECDHE) */ /* Elliptic Curve Groups (ECDHE) */
secp256r1 (23), secp384r1 (24), secp521r1 (25), secp256r1 (23), secp384r1 (24), secp521r1 (25),
x25519 (29), x448 (30), x25519 (29), x448 (30),
/* Finite Field Groups (DHE) */ /* Finite Field Groups (DHE) */
ffdhe2048 (256), ffdhe3072 (257), ffdhe4096 (258), ffdhe2048 (256), ffdhe3072 (257), ffdhe4096 (258),
ffdhe6144 (259), ffdhe8192 (260), ffdhe6144 (259), ffdhe8192 (260),
/* Reserved Code Points */ /* Reserved Code Points */
ffdhe_private_use (0x01FC..0x01FF), ffdhe_private_use (0x01FC..0x01FF),
ecdhe_private_use (0xFE00..0xFEFF), ecdhe_private_use (0xFE00..0xFEFF),
(0xFFFF) (0xFFFF)
} NamedGroup; } NamedGroup;
struct { struct {
NamedGroup named_group_list<1..2^16-1>; NamedGroup named_group_list<2..2^16-1>;
} NamedGroupList; } NamedGroupList;
Elliptic Curve Groups (ECDHE) Indicates support of the corresponding Elliptic Curve Groups (ECDHE) Indicates support of the corresponding
named curve. Note that some curves are also recommended in ANSI named curve. Note that some curves are also recommended in ANSI
X9.62 [X962] and FIPS 186-4 [DSS]. Others are recommended in X9.62 [X962] and FIPS 186-4 [DSS]. Others are recommended in
[RFC7748]. Values 0xFE00 through 0xFEFF are reserved for private [RFC7748]. Values 0xFE00 through 0xFEFF are reserved for private
use. use.
Finite Field Groups (DHE) Indicates support of the corresponding Finite Field Groups (DHE) Indicates support of the corresponding
finite field group, defined in [I-D.ietf-tls-negotiated-ff-dhe]. finite field group, defined in [RFC7919]. Values 0x01FC through
Values 0x01FC through 0x01FF are reserved for private use. 0x01FF are reserved for private use.
Items in named_group_list are ordered according to the client's Items in named_group_list are ordered according to the client's
preferences (most preferred choice first). preferences (most preferred choice first).
As of TLS 1.3, servers are permitted to send the "supported_groups" As of TLS 1.3, servers are permitted to send the "supported_groups"
extension to the client. If the server has a group it prefers to the extension to the client. If the server has a group it prefers to the
ones in the "key_share" extension but is still willing to accept the ones in the "key_share" extension but is still willing to accept the
ClientHello, it SHOULD send "supported_groups" to update the client's ClientHello, it SHOULD send "supported_groups" to update the client's
view of its preferences. Clients MUST NOT act upon any information view of its preferences; this extension SHOULD contain all groups the
found in "supported_groups" prior to successful completion of the server supports, regardless of whether they are currently supported
handshake, but MAY use the information learned from a successfully by the client. Clients MUST NOT act upon any information found in
completed handshake to change what groups they offer to a server in "supported_groups" prior to successful completion of the handshake,
subsequent connections. but MAY use the information learned from a successfully completed
handshake to change what groups they offer to a server in subsequent
connections.
4.2.4. Key Share 4.2.5. Key Share
The "key_share" extension contains the endpoint's cryptographic The "key_share" extension contains the endpoint's cryptographic
parameters. parameters.
Clients MAY send an empty client_shares vector in order to request Clients MAY send an empty client_shares vector in order to request
group selection from the server at the cost of an additional round group selection from the server at the cost of an additional round
trip. (see Section 4.1.4) trip. (see Section 4.1.4)
struct { struct {
NamedGroup group; NamedGroup group;
opaque key_exchange<1..2^16-1>; opaque key_exchange<1..2^16-1>;
} KeyShareEntry; } KeyShareEntry;
group The named group for the key being exchanged. Finite Field group The named group for the key being exchanged. Finite Field
Diffie-Hellman [DH] parameters are described in Section 4.2.4.1; Diffie-Hellman [DH] parameters are described in Section 4.2.5.1;
Elliptic Curve Diffie-Hellman parameters are described in Elliptic Curve Diffie-Hellman parameters are described in
Section 4.2.4.2. Section 4.2.5.2.
key_exchange Key exchange information. The contents of this field key_exchange Key exchange information. The contents of this field
are determined by the specified group and its corresponding are determined by the specified group and its corresponding
definition. Endpoints MUST NOT send empty or otherwise invalid definition. Endpoints MUST NOT send empty or otherwise invalid
key_exchange values for any reason. key_exchange values for any reason.
The "extension_data" field of this extension contains a "KeyShare" The "extension_data" field of this extension contains a "KeyShare"
value: value:
struct { struct {
select (role) { select (Handshake.msg_type) {
case client: case client_hello:
KeyShareEntry client_shares<0..2^16-1>; KeyShareEntry client_shares<0..2^16-1>;
case server: case hello_retry_request:
NamedGroup selected_group;
case server_hello:
KeyShareEntry server_share; KeyShareEntry server_share;
} };
} KeyShare; } KeyShare;
client_shares A list of offered KeyShareEntry values in descending client_shares A list of offered KeyShareEntry values in descending
order of client preference. This vector MAY be empty if the order of client preference. This vector MAY be empty if the
client is requesting a HelloRetryRequest. The ordering of values client is requesting a HelloRetryRequest. The ordering of values
here SHOULD match that of the ordering of offered support in the here SHOULD match that of the ordering of offered support in the
"supported_groups" extension. "supported_groups" extension.
selected_group The mutually supported group the server intends to
negotiate and is requesting a retried ClientHello/KeyShare for.
server_share A single KeyShareEntry value that is in the same group server_share A single KeyShareEntry value that is in the same group
as one of the client's shares. as one of the client's shares.
Clients offer an arbitrary number of KeyShareEntry values, each Clients offer an arbitrary number of KeyShareEntry values, each
representing a single set of key exchange parameters. For instance, representing a single set of key exchange parameters. For instance,
a client might offer shares for several elliptic curves or multiple a client might offer shares for several elliptic curves or multiple
FFDHE groups. The key_exchange values for each KeyShareEntry MUST by FFDHE groups. The key_exchange values for each KeyShareEntry MUST be
generated independently. Clients MUST NOT offer multiple generated independently. Clients MUST NOT offer multiple
KeyShareEntry values for the same group. Clients MUST NOT offer any KeyShareEntry values for the same group. Clients MUST NOT offer any
KeyShareEntry values for groups not listed in the client's KeyShareEntry values for groups not listed in the client's
"supported_groups" extension. Servers MAY check for violations of "supported_groups" extension. Servers MAY check for violations of
these rules and and MAY abort the connection with a fatal these rules and and MAY abort the handshake with an
"illegal_parameter" alert if one is violated. "illegal_parameter" alert if one is violated.
Upon receipt of this extension in a HelloRetryRequest, the client
MUST first verify that the selected_group field corresponds to a
group which was provided in the "supported_groups" extension in the
original ClientHello. It MUST then verify that the selected_group
field does not correspond to a group which was provided in the
"key_share" extension in the original ClientHello. If either of
these checks fails, then the client MUST abort the handshake with an
"illegal_parameter" alert. Otherwise, when sending the new
ClientHello, the client MUST append a new KeyShareEntry for the group
indicated in the selected_group field to the groups in its original
KeyShare. The remaining KeyShareEntry values MUST be preserved.
Note that a HelloRetryRequest might not include the "key_share"
extension if other extensions are sent, such as if the server is only
sending a cookie.
If using (EC)DHE key establishment, servers offer exactly one If using (EC)DHE key establishment, servers offer exactly one
KeyShareEntry. This value MUST correspond to the KeyShareEntry value KeyShareEntry in the ServerHello. This value MUST correspond to the
offered by the client that the server has selected for the negotiated KeyShareEntry value offered by the client that the server has
key exchange. Servers MUST NOT send a KeyShareEntry for any group selected for the negotiated key exchange. Servers MUST NOT send a
not indicated in the "supported_groups" extension. KeyShareEntry for any group not indicated in the "supported_groups"
extension. If a HelloRetryRequest was received, the client MUST
verify that the selected NamedGroup matches that supplied in the
selected_group field and MUST abort the connection with an
"illegal_parameter" alert if it does not.
[[TODO: Recommendation about what the client offers. Presumably [[TODO: Recommendation about what the client offers. Presumably
which integer DH groups and which curves.]] which integer DH groups and which curves.]]
4.2.4.1. Diffie-Hellman Parameters 4.2.5.1. Diffie-Hellman Parameters
Diffie-Hellman [DH] parameters for both clients and servers are Diffie-Hellman [DH] parameters for both clients and servers are
encoded in the opaque key_exchange field of a KeyShareEntry in a encoded in the opaque key_exchange field of a KeyShareEntry in a
KeyShare structure. The opaque value contains the Diffie-Hellman KeyShare structure. The opaque value contains the Diffie-Hellman
public value (Y = g^X mod p), encoded as a big-endian integer, padded public value (Y = g^X mod p), encoded as a big-endian integer, padded
with zeros to the size of p in bytes. with zeros to the size of p in bytes.
Note: For a given Diffie-Hellman group, the padding results in all Note: For a given Diffie-Hellman group, the padding results in all
public keys having the same length. public keys having the same length.
Peers SHOULD validate each other's public key Y by ensuring that 1 < Peers SHOULD validate each other's public key Y by ensuring that 1 <
Y < p-1. This check ensures that the remote peer is properly behaved Y < p-1. This check ensures that the remote peer is properly behaved
and isn't forcing the local system into a small subgroup. and isn't forcing the local system into a small subgroup.
4.2.4.2. ECDHE Parameters 4.2.5.2. ECDHE Parameters
ECDHE parameters for both clients and servers are encoded in the the ECDHE parameters for both clients and servers are encoded in the the
opaque key_exchange field of a KeyShareEntry in a KeyShare structure. opaque key_exchange field of a KeyShareEntry in a KeyShare structure.
For secp256r1, secp384r1 and secp521r1, the contents are the byte For secp256r1, secp384r1 and secp521r1, the contents are the byte
string representation of an elliptic curve public value following the string representation of an elliptic curve public value following the
conversion routine in Section 4.3.6 of ANSI X9.62 [X962]. conversion routine in Section 4.3.6 of ANSI X9.62 [X962].
Although X9.62 supports multiple point formats, any given curve MUST Although X9.62 supports multiple point formats, any given curve MUST
specify only a single point format. All curves currently specified specify only a single point format. All curves currently specified
in this document MUST only be used with the uncompressed point format in this document MUST only be used with the uncompressed point format
(the format for all ECDH functions is considered uncompressed). (the format for all ECDH functions is considered uncompressed).
For x25519 and x448, the contents are the byte string inputs and For x25519 and x448, the contents are the byte string inputs and
outputs of the corresponding functions defined in [RFC7748], 32 bytes outputs of the corresponding functions defined in [RFC7748], 32 bytes
for x25519 and 56 bytes for x448. for x25519 and 56 bytes for x448.
Note: Versions of TLS prior to 1.3 permitted point negotiation; TLS Note: Versions of TLS prior to 1.3 permitted point format
1.3 removes this feature in favor of a single point format for each negotiation; TLS 1.3 removes this feature in favor of a single point
curve. format for each curve.
4.2.5. Pre-Shared Key Extension 4.2.6. Pre-Shared Key Extension
The "pre_shared_key" extension is used to indicate the identity of The "pre_shared_key" extension is used to indicate the identity of
the pre-shared key to be used with a given handshake in association the pre-shared key to be used with a given handshake in association
with PSK key establishment (see [RFC4279] for background). with PSK key establishment (see [RFC4279] for background).
The "extension_data" field of this extension contains a The "extension_data" field of this extension contains a
"PreSharedKeyExtension" value: "PreSharedKeyExtension" value:
enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeModes; enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeMode;
enum { psk_auth(0), psk_sign_auth(1), (255) } PskAuthenticationModes; enum { psk_auth(0), psk_sign_auth(1), (255) } PskAuthenticationMode;
opaque psk_identity<0..2^16-1>;
struct { struct {
PskKeMode ke_modes<1..255>; PskKeyExchangeMode ke_modes<1..255>;
PskAuthMode auth_modes<1..255>; PskAuthenticationMode auth_modes<1..255>;
opaque identity<0..2^16-1>; opaque identity<0..2^16-1>;
} PskIdentity; } PskIdentity;
struct { struct {
select (Role) { select (Handshake.msg_type) {
case client: case client_hello:
psk_identity identities<2..2^16-1>; PskIdentity identities<6..2^16-1>;
case server: case server_hello:
uint16 selected_identity; uint16 selected_identity;
} };
} PreSharedKeyExtension; } PreSharedKeyExtension;
identities A list of the identities (labels for keys) that the identities A list of the identities (labels for keys) that the
client is willing to negotiate with the server. If sent alongside client is willing to negotiate with the server. If sent alongside
the "early_data" extension (see Section 4.2.6), the first identity the "early_data" extension (see Section 4.2.7), the first identity
is the one used for 0-RTT data. is the one used for 0-RTT data.
selected_identity The server's chosen identity expressed as a selected_identity The server's chosen identity expressed as a
(0-based) index into the identies in the client's list. (0-based) index into the identities in the client's list.
Each PSK offered by the client also indicates the authentication and Each PSK offered by the client also indicates the authentication and
key exchange modes with which the server can use it, with each list key exchange modes with which the server can use it, with each list
being in the order of the client's preference, with most preferred being in the order of the client's preference, with most preferred
first. first. Any PSK MUST only be used with a single HKDF hash algorithm.
PskKeyExchangeModes have the following meanings: This restriction is automatically enforced for PSKs established via
NewSessionTicket (Section 4.5.1) but any externally-established PSKs
MUST also follow this rule.
PskKeyExchangeMode values have the following meanings:
psk_ke PSK-only key establishment. In this mode, the server MUST psk_ke PSK-only key establishment. In this mode, the server MUST
not supply a "key_share" value. not supply a "key_share" value.
psk_dhe_ke PSK key establishment with (EC)DHE key establishment. In psk_dhe_ke PSK key establishment with (EC)DHE key establishment. In
this mode, the client and servers MUST supply "key_share" values this mode, the client and servers MUST supply "key_share" values
as described in Section 4.2.4. as described in Section 4.2.5.
PskAuthenticationModes have the following meanings: PskAuthenticationMode values have the following meanings:
psk_auth PSK-only authentication. In this mode, the server MUST NOT psk_auth PSK-only authentication. In this mode, the server MUST NOT
supply either a Certificate or CertificateVerify message. [TODO: supply either a Certificate or CertificateVerify message. [TODO:
Add a signing mode.] Add a signing mode.]
In order to accept PSK key establishment, the server sends a In order to accept PSK key establishment, the server sends a
"pre_shared_key" extension with the selected identity. Clients MUST "pre_shared_key" extension with the selected identity. Clients MUST
verify that the server's selected_identity is within the range verify that the server's selected_identity is within the range
supplied by the client and that the "key_share" and supplied by the client and that the "key_share" and
"signature_algorithms" extensions are consistent with the indicated "signature_algorithms" extensions are consistent with the indicated
ke_modes and auth_modes values. If these values are not consistent, ke_modes and auth_modes values. If these values are not consistent,
the client MUST generate an "illegal_parameter" alert and close the the client MUST abort the handshake with an "illegal_parameter"
connection. alert.
If the server supplies an "early_data" extension, the client MUST If the server supplies an "early_data" extension, the client MUST
verify that the server selected the first offered identity. If any verify that the server selected the first offered identity. If any
other value is returned, the client MUST generate a fatal other value is returned, the client MUST abort the handshake with an
"unknown_psk_identity" alert and close the connection. "unknown_psk_identity" alert.
Note that although 0-RTT data is encrypted with the first PSK Note that although 0-RTT data is encrypted with the first PSK
identity, the server MAY fall back to 1-RTT and select a different identity, the server MAY fall back to 1-RTT and select a different
PSK identity if multiple identities are offered. PSK identity if multiple identities are offered.
4.2.6. Early Data Indication 4.2.7. Early Data Indication
When PSK resumption is used, the client can send application data in When PSK resumption is used, the client can send application data in
its first flight of messages. If the client opts to do so, it MUST its first flight of messages. If the client opts to do so, it MUST
supply an "early_data" extension as well as the "pre_shared_key" supply an "early_data" extension as well as the "pre_shared_key"
extension. extension.
The "extension_data" field of this extension contains an The "extension_data" field of this extension contains an
"EarlyDataIndication" value: "EarlyDataIndication" value:
struct { struct {
select (Role) { select (Handshake.msg_type) {
case client: case client_hello:
uint32 obfuscated_ticket_age; uint32 obfuscated_ticket_age;
case server: case server_hello:
struct {}; struct {};
} };
} EarlyDataIndication; } EarlyDataIndication;
obfuscated_ticket_age The time since the client learned about the obfuscated_ticket_age The time since the client learned about the
server configuration that it is using, in milliseconds. This server configuration that it is using, in milliseconds. This
value is added modulo 2^32 to with the "ticket_age_add" value that value is added modulo 2^32 to with the "ticket_age_add" value that
was included with the ticket, see Section 4.4.1. This addition was included with the ticket, see Section 4.5.1. This addition
prevents passive observers from correlating sessions unless prevents passive observers from correlating sessions unless
tickets are reused. Note: because ticket lifetimes are restricted tickets are reused. Note: because ticket lifetimes are restricted
to a week, 32 bits is enough to represent any plausible age, even to a week, 32 bits is enough to represent any plausible age, even
in milliseconds. in milliseconds.
A server MUST validate that the ticket_age is within a small A server MUST validate that the ticket_age is within a small
tolerance of the time since the ticket was issued (see tolerance of the time since the ticket was issued (see
Section 4.2.6.2). Section 4.2.7.2). If it is not, the server SHOULD proceed with the
handshake but reject 0-RTT.
The parameters for the 0-RTT data (symmetric cipher suite, ALPN, The parameters for the 0-RTT data (symmetric cipher suite, ALPN,
etc.) are the same as those which were negotiated in the connection etc.) are the same as those which were negotiated in the connection
which established the PSK. The PSK used to encrypt the early data which established the PSK. The PSK used to encrypt the early data
MUST be the first PSK listed in the client's "pre_shared_key" MUST be the first PSK listed in the client's "pre_shared_key"
extension. extension.
0-RTT messages sent in the first flight have the same content types 0-RTT messages sent in the first flight have the same content types
as their corresponding messages sent in other flights (handshake, as their corresponding messages sent in other flights (handshake,
application_data, and alert respectively) but are protected under application_data, and alert respectively) but are protected under
different keys. After all the 0-RTT application data messages (if different keys. After all the 0-RTT application data messages (if
any) have been sent, an "end_of_early_data" alert of type "warning" any) have been sent, an "end_of_early_data" alert of type "warning"
is sent to indicate the end of the flight. 0-RTT MUST always be is sent to indicate the end of the flight. 0-RTT MUST always be
followed by an "end_of_early_data" alert. followed by an "end_of_early_data" alert, which will be encrypted
with the 0-RTT traffic keys.
A server which receives an "early_data" extension can behave in one A server which receives an "early_data" extension can behave in one
of two ways: of two ways:
- Ignore the extension and return no response. This indicates that - Ignore the extension and return no response. This indicates that
the server has ignored any early data and an ordinary 1-RTT the server has ignored any early data and an ordinary 1-RTT
handshake is required. handshake is required.
- Return an empty extension, indicating that it intends to process - Return an empty extension, indicating that it intends to process
the early data. It is not possible for the server to accept only the early data. It is not possible for the server to accept only
a subset of the early data messages. a subset of the early data messages.
- Request that the client send another ClientHello by responding
with a HelloRetryRequest. A client MUST NOT include the
"early_data" extension in its followup ClientHello.
In order to accept early data, the server server MUST have accepted a In order to accept early data, the server server MUST have accepted a
PSK cipher suite and selected the the first key offered in the PSK cipher suite and selected the the first key offered in the
client's "pre_shared_key" extension. In addition, it MUST verify client's "pre_shared_key" extension. In addition, it MUST verify
that the following values are consistent with those negotiated in the that the following values are consistent with those negotiated in the
connection during which the ticket was established. connection during which the ticket was established.
- The TLS version number, AEAD algorithm, and the hash for HKDF. - The TLS version number, AEAD algorithm, and the hash for HKDF.
- The selected ALPN [RFC7443] value, if any. - The selected ALPN [RFC7443] value, if any.
- The server_name [RFC6066] value provided by the client, if any.
Future extensions MUST define their interaction with 0-RTT. Future extensions MUST define their interaction with 0-RTT.
If any of these checks fail, the server MUST NOT respond with the If any of these checks fail, the server MUST NOT respond with the
extension and must discard all the remaining first flight data (thus extension and must discard all the remaining first flight data (thus
falling back to 1-RTT). If the client attempts a 0-RTT handshake but falling back to 1-RTT). If the client attempts a 0-RTT handshake but
the server rejects it, it will generally not have the 0-RTT record the server rejects it, it will generally not have the 0-RTT record
protection keys and must instead trial decrypt each record with the protection keys and must instead trial decrypt each record with the
1-RTT handshake keys until it finds one that decrypts properly, and 1-RTT handshake keys until it finds one that decrypts properly, and
then pick up the handshake from that point. then pick up the handshake from that point.
If the server chooses to accept the "early_data" extension, then it If the server chooses to accept the "early_data" extension, then it
MUST comply with the same error handling requirements specified for MUST comply with the same error handling requirements specified for
all records when processing early data records. Specifically, all records when processing early data records. Specifically, if the
decryption failure of any 0-RTT record following an accepted server fails to decrypt any 0-RTT record following an accepted
"early_data" extension MUST produce a fatal "bad_record_mac" alert as "early_data" extension it MUST terminate the connection with a
per Section 5.2. "bad_record_mac" alert as per Section 5.2.
If the server rejects the "early_data" extension, the client If the server rejects the "early_data" extension, the client
application MAY opt to retransmit the data once the handshake has application MAY opt to retransmit the data once the handshake has
been completed. TLS stacks SHOULD not do this automatically and been completed. TLS stacks SHOULD not do this automatically and
client applications MUST take care that the negotiated parameters are client applications MUST take care that the negotiated parameters are
consistent with those it expected. For example, if the ALPN value consistent with those it expected. For example, if the ALPN value
has changed, it is likely unsafe to retransmit the original has changed, it is likely unsafe to retransmit the original
application layer data. application layer data.
4.2.6.1. Processing Order 4.2.7.1. Processing Order
Clients are permitted to "stream" 0-RTT data until they receive the Clients are permitted to "stream" 0-RTT data until they receive the
server's Finished, only then sending the "end_of_early_data" alert. server's Finished, only then sending the "end_of_early_data" alert.
In order to avoid deadlock, when accepting "early_data", servers MUST In order to avoid deadlock, when accepting "early_data", servers MUST
process the client's Finished and then immediately send the process the client's Finished and then immediately send the
ServerHello, rather than waiting for the client's "end_of_early_data" ServerHello, rather than waiting for the client's "end_of_early_data"
alert. alert.
4.2.6.2. Replay Properties 4.2.7.2. Replay Properties
As noted in Section 2.3, TLS provides a limited mechanism for replay As noted in Section 2.3, TLS provides a limited mechanism for replay
protection for data sent by the client in the first flight. protection for data sent by the client in the first flight.
The "obfuscated_ticket_age" parameter in the client's "early_data" The "obfuscated_ticket_age" parameter in the client's "early_data"
extension SHOULD be used by servers to limit the time over which the extension SHOULD be used by servers to limit the time over which the
first flight might be replayed. A server can store the time at which first flight might be replayed. A server can store the time at which
it sends a session ticket to the client, or encode the time in the it sends a session ticket to the client, or encode the time in the
ticket. Then, each time it receives an "early_data" extension, it ticket. Then, each time it receives an "early_data" extension, it
can subtract the base value and check to see if the value used by the can subtract the base value and check to see if the value used by the
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A small allowance for errors in clocks and variations in measurements A small allowance for errors in clocks and variations in measurements
is advisable. However, any allowance also increases the opportunity is advisable. However, any allowance also increases the opportunity
for replay. In this case, it is better to reject early data and fall for replay. In this case, it is better to reject early data and fall
back to a full 1-RTT handshake than to risk greater exposure to back to a full 1-RTT handshake than to risk greater exposure to
replay attacks. In common network topologies for browser clients, replay attacks. In common network topologies for browser clients,
small allowances on the order of ten seconds are reasonable. Clock small allowances on the order of ten seconds are reasonable. Clock
skew distributions are not symmetric, so the optimal tradeoff may skew distributions are not symmetric, so the optimal tradeoff may
involve an asymmetric replay window. involve an asymmetric replay window.
4.2.7. OCSP Status Extensions 4.2.8. OCSP Status Extensions
[RFC6066] and [RFC6961] provide extensions to negotiate the server [RFC6066] and [RFC6961] provide extensions to negotiate the server
sending OCSP responses to the client. In TLS 1.2 and below, the sending OCSP responses to the client. In TLS 1.2 and below, the
server sends an empty extension to indicate negotiation of this server sends an empty extension to indicate negotiation of this
extension and the OCSP information is carried in a CertificateStatus extension and the OCSP information is carried in a CertificateStatus
message. In TLS 1.3, the server's OCSP information is carried in an message. In TLS 1.3, the server's OCSP information is carried in an
extension in EncryptedExtensions. Specifically: The body of the extension in EncryptedExtensions. Specifically: The body of the
"status_request" or "status_request_v2" extension from the server "status_request" or "status_request_v2" extension from the server
MUST be a CertificateStatus structure as defined in [RFC6066] and MUST be a CertificateStatus structure as defined in [RFC6066] and
[RFC6961] respectively. [RFC6961] respectively.
Note: This means that the certificate status appears prior to the Note: This means that the certificate status appears prior to the
certificates it applies to. This is slightly anomalous but matches certificates it applies to. This is slightly anomalous but matches
the existing behavior for SignedCertificateTimestamps [RFC6962], and the existing behavior for SignedCertificateTimestamps [RFC6962], and
is more easily extensible in the handshake state machine. is more easily extensible in the handshake state machine.
4.2.8. Encrypted Extensions 4.3. Server Parameters Messages
The next two messages from the server, EncryptedExtensions and
CertificateRequest, contain encrypted information from the server
that determines the rest of the handshake.
4.3.1. Encrypted Extensions
When this message will be sent: When this message will be sent:
In all handshakes, the server MUST send the EncryptedExtensions In all handshakes, the server MUST send the EncryptedExtensions
message immediately after the ServerHello message. This is the message immediately after the ServerHello message. This is the
first message that is encrypted under keys derived from first message that is encrypted under keys derived from
handshake_traffic_secret. handshake_traffic_secret.
Meaning of this message: Meaning of this message:
The EncryptedExtensions message contains any extensions which The EncryptedExtensions message contains any extensions which
should be protected, i.e., any which are not needed to establish should be protected, i.e., any which are not needed to establish
the cryptographic context. the cryptographic context.
The same extension types MUST NOT appear in both the ServerHello and The same extension types MUST NOT appear in both the ServerHello and
EncryptedExtensions. If the same extension appears in both EncryptedExtensions. All server-sent extensions other than those
locations, the client MUST rely only on the value in the explicitly listed in Section 4.1.3 or designated in the IANA registry
EncryptedExtensions block. All server-sent extensions other than MUST only appear in EncryptedExtensions. Extensions which are
those explicitly listed in Section 4.1.3 or designated in the IANA designated to appear in ServerHello MUST NOT appear in
registry MUST only appear in EncryptedExtensions. Extensions which
are designated to appear in ServerHello MUST NOT appear in
EncryptedExtensions. Clients MUST check EncryptedExtensions for the EncryptedExtensions. Clients MUST check EncryptedExtensions for the
presence of any forbidden extensions and if any are found MUST presence of any forbidden extensions and if any are found MUST abort
terminate the handshake with an "illegal_parameter" alert. the handshake with an "illegal_parameter" alert.
Structure of this message: Structure of this message:
struct { struct {
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} EncryptedExtensions; } EncryptedExtensions;
extensions A list of extensions. extensions A list of extensions.
4.2.9. Certificate Request 4.3.2. Certificate Request
When this message will be sent: When this message will be sent:
A server which is authenticating with a certificate can optionally A server which is authenticating with a certificate can optionally
request a certificate from the client. This message, if sent, request a certificate from the client. This message, if sent,
will follow EncryptedExtensions. will follow EncryptedExtensions.
Structure of this message: Structure of this message:
opaque DistinguishedName<1..2^16-1>; opaque DistinguishedName<1..2^16-1>;
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values (e.g. Extended Key Usage). If the server has included a values (e.g. Extended Key Usage). If the server has included a
non-empty certificate_extensions list, the client certificate MUST non-empty certificate_extensions list, the client certificate MUST
contain all of the specified extension OIDs that the client contain all of the specified extension OIDs that the client
recognizes. For each extension OID recognized by the client, all recognizes. For each extension OID recognized by the client, all
of the specified values MUST be present in the client certificate of the specified values MUST be present in the client certificate
(but the certificate MAY have other values as well). However, the (but the certificate MAY have other values as well). However, the
client MUST ignore and skip any unrecognized certificate extension client MUST ignore and skip any unrecognized certificate extension
OIDs. If the client has ignored some of the required certificate OIDs. If the client has ignored some of the required certificate
extension OIDs, and supplied a certificate that does not satisfy extension OIDs, and supplied a certificate that does not satisfy
the request, the server MAY at its discretion either continue the the request, the server MAY at its discretion either continue the
session without client authentication, or terminate the session session without client authentication, or abort the handshake with
with a fatal unsupported_certificate alert. PKIX RFCs define a an "unsupported_certificate" alert. PKIX RFCs define a variety of
variety of certificate extension OIDs and their corresponding certificate extension OIDs and their corresponding value types.
value types. Depending on the type, matching certificate Depending on the type, matching certificate extension values are
extension values are not necessarily bitwise-equal. It is not necessarily bitwise-equal. It is expected that TLS
expected that TLS implementations will rely on their PKI libraries implementations will rely on their PKI libraries to perform
to perform certificate selection using certificate extension OIDs. certificate selection using certificate extension OIDs. This
This document defines matching rules for two standard certificate document defines matching rules for two standard certificate
extensions defined in [RFC5280]: extensions defined in [RFC5280]:
o The Key Usage extension in a certificate matches the request o The Key Usage extension in a certificate matches the request
when all key usage bits asserted in the request are also when all key usage bits asserted in the request are also
asserted in the Key Usage certificate extension. asserted in the Key Usage certificate extension.
o The Extended Key Usage extension in a certificate matches the o The Extended Key Usage extension in a certificate matches the
request when all key purpose OIDs present in the request are request when all key purpose OIDs present in the request are
also found in the Extended Key Usage certificate extension. also found in the Extended Key Usage certificate extension.
The special anyExtendedKeyUsage OID MUST NOT be used in the The special anyExtendedKeyUsage OID MUST NOT be used in the
request. request.
Separate specifications may define matching rules for other Separate specifications may define matching rules for other
certificate extensions. certificate extensions.
Note: It is a fatal "unexpected_message" alert for an anonymous Servers which are authenticating with a PSK MUST not send the
server to request client authentication. CertificateRequest message.
4.3. Authentication Messages 4.4. Authentication Messages
As discussed in Section 2, TLS uses a common set of messages for As discussed in Section 2, TLS uses a common set of messages for
authentication, key confirmation, and handshake integrity: authentication, key confirmation, and handshake integrity:
Certificate, CertificateVerify, and Finished. These messages are Certificate, CertificateVerify, and Finished. These messages are
always sent as the last messages in their handshake flight. The always sent as the last messages in their handshake flight. The
Certificate and CertificateVerify messages are only sent under Certificate and CertificateVerify messages are only sent under
certain circumstances, as defined below. The Finished message is certain circumstances, as defined below. The Finished message is
always sent as part of the Authentication block. always sent as part of the Authentication block.
The computations for the Authentication messages all uniformly take The computations for the Authentication messages all uniformly take
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- A base key to be used to compute a MAC key. - A base key to be used to compute a MAC key.
Based on these inputs, the messages then contain: Based on these inputs, the messages then contain:
Certificate The certificate to be used for authentication and any Certificate The certificate to be used for authentication and any
supporting certificates in the chain. Note that certificate-based supporting certificates in the chain. Note that certificate-based
client authentication is not available in the 0-RTT case. client authentication is not available in the 0-RTT case.
CertificateVerify A signature over the value Hash(Handshake Context CertificateVerify A signature over the value Hash(Handshake Context
+ Certificate) + Hash(resumption_context) See Section 4.4.1 for + Certificate) + Hash(resumption_context) See Section 4.5.1 for
the definition of resumption_context. the definition of resumption_context.
Finished A MAC over the value Hash(Handshake Context + Certificate + Finished A MAC over the value Hash(Handshake Context + Certificate +
CertificateVerify) + Hash(resumption_context) using a MAC key CertificateVerify) + Hash(resumption_context) using a MAC key
derived from the base key. derived from the base key.
Because the CertificateVerify signs the Handshake Context + Because the CertificateVerify signs the Handshake Context +
Certificate and the Finished MACs the Handshake Context + Certificate Certificate and the Finished MACs the Handshake Context + Certificate
+ CertificateVerify, this is mostly equivalent to keeping a running + CertificateVerify, this is mostly equivalent to keeping a running
hash of the handshake messages (exactly so in the pure 1-RTT cases). hash of the handshake messages (exactly so in the pure 1-RTT cases).
Note, however, that subsequent post-handshake authentications do not Note, however, that subsequent post-handshake authentications do not
include each other, just the messages through the end of the main include each other, just the messages through the end of the main
handshake. handshake.
The following table defines the Handshake Context and MAC Base Key The following table defines the Handshake Context and MAC Base Key
for each scenario: for each scenario:
+------------+--------------------------------+---------------------+ +-----------+-----------------------------+-------------------------+
| Mode | Handshake Context | Base Key | | Mode | Handshake Context | Base Key |
+------------+--------------------------------+---------------------+ +-----------+-----------------------------+-------------------------+
| 0-RTT | ClientHello | early_traffic_secre | | 0-RTT | ClientHello | client_early_traffic_se |
| | | t | | | | cret |
| | | | | | | |
| 1-RTT | ClientHello ... later of Encry | handshake_traffic_s | | 1-RTT | ClientHello ... later of En | [sender]_handshake_traf |
| (Server) | ptedExtensions/CertificateRequ | ecret | | (Server) | cryptedExtensions/Certifica | fic_secret |
| | est | | | | teRequest | |
| | | | | | | |
| 1-RTT | ClientHello ... ServerFinished | handshake_traffic_s | | 1-RTT | ClientHello ... | [sender]_handshake_traf |
| (Client) | | ecret | | (Client) | ServerFinished | fic_secret |
| | | | | | | |
| Post- | ClientHello ... ClientFinished | traffic_secret_0 | | Post- | ClientHello ... | [sender]_traffic_secret |
| Handshake | + CertificateRequest | | | Handshake | ClientFinished + | _N |
+------------+--------------------------------+---------------------+ | | CertificateRequest | |
+-----------+-----------------------------+-------------------------+
The [sender] in this table denotes the sending side.
Note: The Handshake Context for the last three rows does not include Note: The Handshake Context for the last three rows does not include
any 0-RTT handshake messages, regardless of whether 0-RTT is used. any 0-RTT handshake messages, regardless of whether 0-RTT is used.
4.3.1. Certificate 4.4.1. Certificate
When this message will be sent: When this message will be sent:
The server MUST send a Certificate message whenever the agreed- The server MUST send a Certificate message whenever the agreed-
upon key exchange method uses certificates for authentication upon key exchange method uses certificates for authentication
(this includes all key exchange methods defined in this document (this includes all key exchange methods defined in this document
except PSK). except PSK).
The client MUST send a Certificate message if and only if server The client MUST send a Certificate message if and only if server
has requested client authentication via a CertificateRequest has requested client authentication via a CertificateRequest
message (Section 4.2.9). If the server requests client message (Section 4.3.2). If the server requests client
authentication but no suitable certificate is available, the authentication but no suitable certificate is available, the
client MUST send a Certificate message containing no certificates client MUST send a Certificate message containing no certificates
(i.e., with the "certificate_list" field having length 0). (i.e., with the "certificate_list" field having length 0).
Meaning of this message: Meaning of this message:
This message conveys the endpoint's certificate chain to the peer. This message conveys the endpoint's certificate chain to the peer.
Structure of this message: Structure of this message:
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nonetheless be validated properly. For maximum compatibility, all nonetheless be validated properly. For maximum compatibility, all
implementations SHOULD be prepared to handle potentially extraneous implementations SHOULD be prepared to handle potentially extraneous
certificates and arbitrary orderings from any TLS version, with the certificates and arbitrary orderings from any TLS version, with the
exception of the end-entity certificate which MUST be first. exception of the end-entity certificate which MUST be first.
The server's certificate list MUST always be non-empty. A client The server's certificate list MUST always be non-empty. A client
will send an empty certificate list if it does not have an will send an empty certificate list if it does not have an
appropriate certificate to send in response to the server's appropriate certificate to send in response to the server's
authentication request. authentication request.
4.3.1.1. Server Certificate Selection 4.4.1.1. Server Certificate Selection
The following rules apply to the certificates sent by the server: The following rules apply to the certificates sent by the server:
- The certificate type MUST be X.509v3 [RFC5280], unless explicitly - The certificate type MUST be X.509v3 [RFC5280], unless explicitly
negotiated otherwise (e.g., [RFC5081]). negotiated otherwise (e.g., [RFC5081]).
- The server's end-entity certificate's public key (and associated - The server's end-entity certificate's public key (and associated
restrictions) MUST be compatible with the selected authentication restrictions) MUST be compatible with the selected authentication
algorithm (currently RSA or ECDSA). algorithm (currently RSA or ECDSA).
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"signature_algorithms" extension. "signature_algorithms" extension.
- The "server_name" and "trusted_ca_keys" extensions [RFC6066] are - The "server_name" and "trusted_ca_keys" extensions [RFC6066] are
used to guide certificate selection. As servers MAY require the used to guide certificate selection. As servers MAY require the
presence of the "server_name" extension, clients SHOULD send this presence of the "server_name" extension, clients SHOULD send this
extension, when applicable. extension, when applicable.
All certificates provided by the server MUST be signed by a signature All certificates provided by the server MUST be signed by a signature
algorithm that appears in the "signature_algorithms" extension algorithm that appears in the "signature_algorithms" extension
provided by the client, if they are able to provide such a chain (see provided by the client, if they are able to provide such a chain (see
Section 4.2.2). Certificates that are self-signed or certificates Section 4.2.3). Certificates that are self-signed or certificates
that are expected to be trust anchors are not validated as part of that are expected to be trust anchors are not validated as part of
the chain and therefore MAY be signed with any algorithm. the chain and therefore MAY be signed with any algorithm.
If the server cannot produce a certificate chain that is signed only If the server cannot produce a certificate chain that is signed only
via the indicated supported algorithms, then it SHOULD continue the via the indicated supported algorithms, then it SHOULD continue the
handshake by sending the client a certificate chain of its choice handshake by sending the client a certificate chain of its choice
that may include algorithms that are not known to be supported by the that may include algorithms that are not known to be supported by the
client. This fallback chain MAY use the deprecated SHA-1 hash client. This fallback chain MAY use the deprecated SHA-1 hash
algorithm only if the "signature_algorithms" extension provided by algorithm only if the "signature_algorithms" extension provided by
the client permits it. If the client cannot construct an acceptable the client permits it. If the client cannot construct an acceptable
chain using the provided certificates and decides to abort the chain using the provided certificates and decides to abort the
handshake, then it MUST send an "unsupported_certificate" alert handshake, then it MUST abort the handshake with an
message and close the connection. "unsupported_certificate" alert.
If the server has multiple certificates, it chooses one of them based If the server has multiple certificates, it chooses one of them based
on the above-mentioned criteria (in addition to other criteria, such on the above-mentioned criteria (in addition to other criteria, such
as transport layer endpoint, local configuration and preferences). as transport layer endpoint, local configuration and preferences).
4.3.1.2. Client Certificate Selection 4.4.1.2. Client Certificate Selection
The following rules apply to certificates sent by the client: The following rules apply to certificates sent by the client:
In particular: In particular:
- The certificate type MUST be X.509v3 [RFC5280], unless explicitly - The certificate type MUST be X.509v3 [RFC5280], unless explicitly
negotiated otherwise (e.g., [RFC5081]). negotiated otherwise (e.g., [RFC5081]).
- If the certificate_authorities list in the certificate request - If the certificate_authorities list in the certificate request
message was non-empty, one of the certificates in the certificate message was non-empty, one of the certificates in the certificate
chain SHOULD be issued by one of the listed CAs. chain SHOULD be issued by one of the listed CAs.
- The certificates MUST be signed using an acceptable signature - The certificates MUST be signed using an acceptable signature
algorithm, as described in Section 4.2.9. Note that this relaxes algorithm, as described in Section 4.3.2. Note that this relaxes
the constraints on certificate-signing algorithms found in prior the constraints on certificate-signing algorithms found in prior
versions of TLS. versions of TLS.
- If the certificate_extensions list in the certificate request - If the certificate_extensions list in the certificate request
message was non-empty, the end-entity certificate MUST match the message was non-empty, the end-entity certificate MUST match the
extension OIDs recognized by the client, as described in extension OIDs recognized by the client, as described in
Section 4.2.9. Section 4.3.2.
Note that, as with the server certificate, there are certificates Note that, as with the server certificate, there are certificates
that use algorithm combinations that cannot be currently used with that use algorithm combinations that cannot be currently used with
TLS. TLS.
4.3.1.3. Receiving a Certificate Message 4.4.1.3. Receiving a Certificate Message
In general, detailed certificate validation procedures are out of In general, detailed certificate validation procedures are out of
scope for TLS (see [RFC5280]). This section provides TLS-specific scope for TLS (see [RFC5280]). This section provides TLS-specific
requirements. requirements.
If the server supplies an empty Certificate message, the client MUST If the server supplies an empty Certificate message, the client MUST
terminate the handshake with a fatal "decode_error" alert. abort the handshake with a "decode_error" alert.
If the client does not send any certificates, the server MAY at its If the client does not send any certificates, the server MAY at its
discretion either continue the handshake without client discretion either continue the handshake without client
authentication, or respond with a fatal "handshake_failure" alert. authentication, or abort the handshake with a "certificate_required"
Also, if some aspect of the certificate chain was unacceptable (e.g., alert. Also, if some aspect of the certificate chain was
it was not signed by a known, trusted CA), the server MAY at its unacceptable (e.g., it was not signed by a known, trusted CA), the
discretion either continue the handshake (considering the client server MAY at its discretion either continue the handshake
unauthenticated) or send a fatal alert. (considering the client unauthenticated) or abort the handshake.
Any endpoint receiving any certificate signed using any signature Any endpoint receiving any certificate signed using any signature
algorithm using an MD5 hash MUST send a "bad_certificate" alert algorithm using an MD5 hash MUST abort the handshake with a
message and close the connection. SHA-1 is deprecated and therefore "bad_certificate" alert. SHA-1 is deprecated and it is RECOMMENDED
NOT RECOMMENDED. All endpoints are RECOMMENDED to transition to that any endpoint receiving any certificate signed using any
SHA-256 or better as soon as possible to maintain interoperability signature algorithm using a SHA-1 hash abort the handshake with a
"bad_certificate" alert. All endpoints are RECOMMENDED to transition
to SHA-256 or better as soon as possible to maintain interoperability
with implementations currently in the process of phasing out SHA-1 with implementations currently in the process of phasing out SHA-1
support. support.
Note that a certificate containing a key for one signature algorithm Note that a certificate containing a key for one signature algorithm
MAY be signed using a different signature algorithm (for instance, an MAY be signed using a different signature algorithm (for instance, an
RSA key signed with an ECDSA key). RSA key signed with an ECDSA key).
Endpoints that reject certification paths due to use of a deprecated 4.4.2. Certificate Verify
hash MUST send a fatal "bad_certificate" alert message before closing
the connection.
4.3.2. Certificate Verify
When this message will be sent: When this message will be sent:
This message is used to provide explicit proof that an endpoint This message is used to provide explicit proof that an endpoint
possesses the private key corresponding to its certificate and possesses the private key corresponding to its certificate and
also provides integrity for the handshake up to this point. also provides integrity for the handshake up to this point.
Servers MUST send this message when authenticating via a Servers MUST send this message when authenticating via a
certificate. Clients MUST send this message whenever certificate. Clients MUST send this message whenever
authenticating via a Certificate (i.e., when the Certificate authenticating via a Certificate (i.e., when the Certificate
message is non-empty). When sent, this message MUST appear message is non-empty). When sent, this message MUST appear
skipping to change at page 52, line 43 skipping to change at page 55, line 18
the Finished message. the Finished message.
Structure of this message: Structure of this message:
struct { struct {
SignatureScheme algorithm; SignatureScheme algorithm;
opaque signature<0..2^16-1>; opaque signature<0..2^16-1>;
} CertificateVerify; } CertificateVerify;
The algorithm field specifies the signature algorithm used (see The algorithm field specifies the signature algorithm used (see
Section 4.2.2 for the definition of this field). The signature is a Section 4.2.3 for the definition of this field). The signature is a
digital signature using that algorithm that covers the hash output digital signature using that algorithm that covers the hash output
described in Section 4.3 namely: described in Section 4.4 namely:
Hash(Handshake Context + Certificate) + Hash(resumption_context) Hash(Handshake Context + Certificate) + Hash(resumption_context)
In TLS 1.3, the digital signature process takes as input: In TLS 1.3, the digital signature process takes as input:
- A signing key - A signing key
- A context string - A context string
- The actual content to be signed - The actual content to be signed
The digital signature is then computed using the signing key over the The digital signature is then computed using the signing key over the
concatenation of: concatenation of:
- 64 bytes of octet 32 - 64 bytes of octet 32
- The context string - The context string
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2020202020202020202020202020202020202020202020202020202020202020 2020202020202020202020202020202020202020202020202020202020202020
544c5320312e332c207365727665722043657274696669636174655665726966 544c5320312e332c207365727665722043657274696669636174655665726966
79 79
00 00
0101010101010101010101010101010101010101010101010101010101010101 0101010101010101010101010101010101010101010101010101010101010101
0202020202020202020202020202020202020202020202020202020202020202 0202020202020202020202020202020202020202020202020202020202020202
If sent by a server, the signature algorithm MUST be one offered in If sent by a server, the signature algorithm MUST be one offered in
the client's "signature_algorithms" extension unless no valid the client's "signature_algorithms" extension unless no valid
certificate chain can be produced without unsupported algorithms (see certificate chain can be produced without unsupported algorithms (see
Section 4.2.2). Section 4.2.3).
If sent by a client, the signature algorithm used in the signature If sent by a client, the signature algorithm used in the signature
MUST be one of those present in the supported_signature_algorithms MUST be one of those present in the supported_signature_algorithms
field of the CertificateRequest message. field of the CertificateRequest message.
In addition, the signature algorithm MUST be compatible with the key In addition, the signature algorithm MUST be compatible with the key
in the sender's end-entity certificate. RSA signatures MUST use an in the sender's end-entity certificate. RSA signatures MUST use an
RSASSA-PSS algorithm, regardless of whether RSASSA-PKCS1-v1_5 RSASSA-PSS algorithm, regardless of whether RSASSA-PKCS1-v1_5
algorithms appear in "signature_algorithms". SHA-1 MUST NOT be used algorithms appear in "signature_algorithms". SHA-1 MUST NOT be used
in any signatures in CertificateVerify. All SHA-1 signature in any signatures in CertificateVerify. All SHA-1 signature
skipping to change at page 54, line 20 skipping to change at page 56, line 45
Note: When used with non-certificate-based handshakes (e.g., PSK), Note: When used with non-certificate-based handshakes (e.g., PSK),
the client's signature does not cover the server's certificate the client's signature does not cover the server's certificate
directly, although it does cover the server's Finished message, which directly, although it does cover the server's Finished message, which
transitively includes the server's certificate when the PSK derives transitively includes the server's certificate when the PSK derives
from a certificate-authenticated handshake. [PSK-FINISHED] describes from a certificate-authenticated handshake. [PSK-FINISHED] describes
a concrete attack on this mode if the Finished is omitted from the a concrete attack on this mode if the Finished is omitted from the
signature. It is unsafe to use certificate-based client signature. It is unsafe to use certificate-based client
authentication when the client might potentially share the same PSK/ authentication when the client might potentially share the same PSK/
key-id pair with two different endpoints. In order to ensure this, key-id pair with two different endpoints. In order to ensure this,
implementations MUST NOT mix certificate-based client authentication implementations MUST NOT mix certificate-based client authentication
with pure PSK modes (i.e., those where the PSK was not derived from a with PSK.
previous non-PSK handshake).
4.3.3. Finished 4.4.3. Finished
When this message will be sent: When this message will be sent:
The Finished message is the final message in the authentication The Finished message is the final message in the authentication
block. It is essential for providing authentication of the block. It is essential for providing authentication of the
handshake and of the computed keys. handshake and of the computed keys.
Meaning of this message: Meaning of this message:
Recipients of Finished messages MUST verify that the contents are Recipients of Finished messages MUST verify that the contents are
correct. Once a side has sent its Finished message and received correct. Once a side has sent its Finished message and received
and validated the Finished message from its peer, it may begin to and validated the Finished message from its peer, it may begin to
send and receive application data over the connection. send and receive application data over the connection.
The key used to compute the finished message is computed from the The key used to compute the finished message is computed from the
Base key defined in Section 4.3 using HKDF (see Section 7.1). Base key defined in Section 4.4 using HKDF (see Section 7.1).
Specifically: Specifically:
client_finished_key = finished_key =
HKDF-Expand-Label(BaseKey, "client finished", "", Hash.Length) HKDF-Expand-Label(BaseKey, "finished", "", Hash.length)
server_finished_key =
HKDF-Expand-Label(BaseKey, "server finished", "", Hash.Length)
Structure of this message: Structure of this message:
struct { struct {
opaque verify_data[Hash.length]; opaque verify_data[Hash.length];
} Finished; } Finished;
The verify_data value is computed as follows: The verify_data value is computed as follows:
verify_data = verify_data =
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output for the Hash used for the handshake. output for the Hash used for the handshake.
Note: Alerts and any other record types are not handshake messages Note: Alerts and any other record types are not handshake messages
and are not included in the hash computations. and are not included in the hash computations.
Any records following a 1-RTT Finished message MUST be encrypted Any records following a 1-RTT Finished message MUST be encrypted
under the application traffic key. In particular, this includes any under the application traffic key. In particular, this includes any
alerts sent by the server in response to client Certificate and alerts sent by the server in response to client Certificate and
CertificateVerify messages. CertificateVerify messages.
4.4. Post-Handshake Messages 4.5. Post-Handshake Messages
TLS also allows other messages to be sent after the main handshake. TLS also allows other messages to be sent after the main handshake.
These messages use a handshake content type and are encrypted under These messages use a handshake content type and are encrypted under
the application traffic key. the application traffic key.
Handshake messages sent after the handshake MUST NOT be interleaved Handshake messages sent after the handshake MUST NOT be interleaved
with other record types. That is, if a message is split over two or with other record types. That is, if a message is split over two or
more handshake records, there MUST NOT be any other records between more handshake records, there MUST NOT be any other records between
them. them.
4.4.1. New Session Ticket Message 4.5.1. New Session Ticket Message
At any time after the server has received the client Finished At any time after the server has received the client Finished
message, it MAY send a NewSessionTicket message. This message message, it MAY send a NewSessionTicket message. This message
creates a pre-shared key (PSK) binding between the ticket value and creates a pre-shared key (PSK) binding between the ticket value and
the following two values derived from the resumption master secret: the following two values derived from the resumption master secret:
resumption_psk = HKDF-Expand-Label( resumption_psk = HKDF-Expand-Label(
resumption_secret, resumption_secret,
"resumption psk", "", Hash.Length) "resumption psk", "", Hash.length)
resumption_context = HKDF-Expand-Label( resumption_context = HKDF-Expand-Label(
resumption_secret, resumption_secret,
"resumption context", "", Hash.Length) "resumption context", "", Hash.length)
The client MAY use this PSK for future handshakes by including the The client MAY use this PSK for future handshakes by including the
ticket value in the "pre_shared_key" extension in its ClientHello ticket value in the "pre_shared_key" extension in its ClientHello
(Section 4.2.5). Servers MAY send multiple tickets on a single (Section 4.2.6). Servers MAY send multiple tickets on a single
connection, either immediately after each other or after specific connection, either immediately after each other or after specific
events. For instance, the server might send a new ticket after post- events. For instance, the server might send a new ticket after post-
handshake authentication in order to encapsulate the additional handshake authentication in order to encapsulate the additional
client authentication state. Clients SHOULD attempt to use each client authentication state. Clients SHOULD attempt to use each
ticket no more than once, with more recent tickets being used first. ticket no more than once, with more recent tickets being used first.
For handshakes that do not use a resumption_psk, the For handshakes that do not use a resumption_psk, the
resumption_context is a string of Hash.Length zeroes. [[Note: this resumption_context is a string of Hash.length zeroes. [[Note: this
will not be safe if/when we add additional server signatures with will not be safe if/when we add additional server signatures with
PSK: OPEN ISSUE https://github.com/tlswg/tls13-spec/issues/558]] PSK: OPEN ISSUE https://github.com/tlswg/tls13-spec/issues/558]]
Any ticket MUST only be resumed with a cipher suite that is identical Any ticket MUST only be resumed with a cipher suite that is identical
to that negotiated connection where the ticket was established. to that negotiated connection where the ticket was established.
enum { (65535) } TicketExtensionType; enum { ticket_early_data_info(1), (65535) } TicketExtensionType;
struct { struct {
TicketExtensionType extension_type; TicketExtensionType extension_type;
opaque extension_data<1..2^16-1>; opaque extension_data<1..2^16-1>;
} TicketExtension; } TicketExtension;
struct { struct {
uint32 ticket_lifetime; uint32 ticket_lifetime;
PskKeMode ke_modes<1..255>; PskKeyExchangeMode ke_modes<1..255>;
PskAuthMode auth_modes<1..255>; PskAuthenticationMode auth_modes<1..255>;
opaque ticket<1..2^16-1>; opaque ticket<1..2^16-1>;
TicketExtension extensions<0..2^16-2>; TicketExtension extensions<0..2^16-2>;
} NewSessionTicket; } NewSessionTicket;
ke_modes The key exchange modes with which this ticket can be used ke_modes The key exchange modes with which this ticket can be used
in descending order of server preference. in descending order of server preference.
auth_modes The authentication modes with which this ticket can be auth_modes The authentication modes with which this ticket can be
used in descending order of server preference. used in descending order of server preference.
ticket_lifetime Indicates the lifetime in seconds as a 32-bit ticket_lifetime Indicates the lifetime in seconds as a 32-bit
unsigned integer in network byte order from the time of ticket unsigned integer in network byte order from the time of ticket
issuance. Servers MUST NOT use any value more than 604800 seconds issuance. Servers MUST NOT use any value more than 604800 seconds
skipping to change at page 57, line 34 skipping to change at page 59, line 52
ticket_extensions A set of extension values for the ticket. Clients ticket_extensions A set of extension values for the ticket. Clients
MUST ignore unrecognized extensions. MUST ignore unrecognized extensions.
This document defines one ticket extension, "ticket_early_data_info" This document defines one ticket extension, "ticket_early_data_info"
struct { struct {
uint32 ticket_age_add; uint32 ticket_age_add;
} TicketEarlyDataInfo; } TicketEarlyDataInfo;
This extension indicates that the ticket may be used to send 0-RTT This extension indicates that the ticket may be used to send 0-RTT
data (Section 4.2.6)). It contains one value: data (Section 4.2.7)). It contains one value:
ticket_age_add A randomly generated 32-bit value that is used to ticket_age_add A randomly generated 32-bit value that is used to
obscure the age of the ticket that the client includes in the obscure the age of the ticket that the client includes in the
"early_data" extension. The client-side ticket age is added to "early_data" extension. The client-side ticket age is added to
this value modulo 2^32 to obtain the value that is transmitted by this value modulo 2^32 to obtain the value that is transmitted by
the client. the client.
4.4.2. Post-Handshake Authentication 4.5.2. Post-Handshake Authentication
The server is permitted to request client authentication at any time The server is permitted to request client authentication at any time
after the handshake has completed by sending a CertificateRequest after the handshake has completed by sending a CertificateRequest
message. The client SHOULD respond with the appropriate message. The client SHOULD respond with the appropriate
Authentication messages. If the client chooses to authenticate, it Authentication messages. If the client chooses to authenticate, it
MUST send Certificate, CertificateVerify, and Finished. If it MUST send Certificate, CertificateVerify, and Finished. If it
declines, it MUST send a Certificate message containing no declines, it MUST send a Certificate message containing no
certificates followed by Finished. certificates followed by Finished.
Note: Because client authentication may require prompting the user, Note: Because client authentication may require prompting the user,
servers MUST be prepared for some delay, including receiving an servers MUST be prepared for some delay, including receiving an
arbitrary number of other messages between sending the arbitrary number of other messages between sending the
CertificateRequest and receiving a response. In addition, clients CertificateRequest and receiving a response. In addition, clients
which receive multiple CertificateRequests in close succession MAY which receive multiple CertificateRequests in close succession MAY
respond to them in a different order than they were received (the respond to them in a different order than they were received (the
certificate_request_context value allows the server to disambiguate certificate_request_context value allows the server to disambiguate
the responses). the responses).
4.4.3. Key and IV Update 4.5.3. Key and IV Update
struct {} KeyUpdate; enum { update_not_requested(0), update_requested(1), (255)
} KeyUpdateRequest;
struct {
KeyUpdateRequest request_update;
} KeyUpdate;
request_update Indicates that the recipient of the KeyUpdate should
respond with its own KeyUpdate. If an implementation receives any
other value, it MUST terminate the connection with an
"illegal_parameter" alert.
The KeyUpdate handshake message is used to indicate that the sender The KeyUpdate handshake message is used to indicate that the sender
is updating its sending cryptographic keys. This message can be sent is updating its sending cryptographic keys. This message can be sent
by the server after sending its first flight and the client after by the server after sending its first flight and the client after
sending its second flight. Implementations that receive a KeyUpdate sending its second flight. Implementations that receive a KeyUpdate
message prior to receiving a Finished message as part of the 1-RTT message prior to receiving a Finished message as part of the 1-RTT
handshake MUST generate a fatal "unexpected_message" alert. After handshake MUST terminate the connection with an "unexpected_message"
sending a KeyUpdate message, the sender SHALL send all its traffic alert. After sending a KeyUpdate message, the sender SHALL send all
using the next generation of keys, computed as described in its traffic using the next generation of keys, computed as described
Section 7.2. Upon receiving a KeyUpdate, the receiver MUST update in Section 7.2. Upon receiving a KeyUpdate, the receiver MUST update
their receiving keys and if they have not already updated their its receiving keys.
sending state up to or past the then current receiving generation
MUST send their own KeyUpdate prior to sending any other messages.
This mechanism allows either side to force an update to the entire
connection. Note that implementations may receive an arbitrary
number of messages between sending a KeyUpdate and receiving the
peer's KeyUpdate because those messages may already be in flight.
Note that if implementations independently send their own KeyUpdates If the request_udate field is set to "update_requested" then the
and they cross in flight, this only results in an update of one receiver MUST send a KeyUpdate of its own with request_update set to
generation; when each side receives the other side's update it just "update_not_requested" prior to sending its next application data
updates its receive keys and notes that the generations match and record. This mechanism allows either side to force an update to the
thus no send update is needed. entire connection, but causes an implementation which receives
multiple KeyUpdates while it is silent to respond with a single
update. Note that implementations may receive an arbitrary number of
messages between sending a KeyUpdate and receiving the peer's
KeyUpdate because those messages may already be in flight. However,
because send and receive keys are derived from independent traffic
secrets, retaining the receive traffic secret does not threaten the
forward secrecy of data sent before the sender changed keys.
Note that the side which sends its KeyUpdate first needs to retain If implementations independently send their own KeyUpdates with
its receive traffic keys (though not the traffic secret) for the request_update set to "update_requested", and they cross in flight,
previous generation of keys until it receives the KeyUpdate from the then each side will also send a response, with the result that each
other side. side increments by two generations.
Both sender and receiver MUST encrypt their KeyUpdate messages with Both sender and receiver MUST encrypt their KeyUpdate messages with
the old keys. Additionally, both sides MUST enforce that a KeyUpdate the old keys. Additionally, both sides MUST enforce that a KeyUpdate
with the old key is received before accepting any messages encrypted with the old key is received before accepting any messages encrypted
with the new key. Failure to do so may allow message truncation with the new key. Failure to do so may allow message truncation
attacks. attacks.
4.5. Handshake Layer and Key Changes 4.6. Handshake Layer and Key Changes
Handshake messages MUST NOT span key changes. Because the Handshake messages MUST NOT span key changes. Because the
ServerHello, Finished, and KeyUpdate messages signal a key change, ServerHello, Finished, and KeyUpdate messages signal a key change,
upon receiving these messages a receiver MUST verify that the end of upon receiving these messages a receiver MUST verify that the end of
these messages aligns with a record boundary; if not, then it MUST these messages aligns with a record boundary; if not, then it MUST
send a fatal "unexpected_message" alert. terminate the connection with an "unexpected_message" alert.
5. Record Protocol 5. Record Protocol
The TLS record protocol takes messages to be transmitted, fragments The TLS record protocol takes messages to be transmitted, fragments
the data into manageable blocks, protects the records, and transmits the data into manageable blocks, protects the records, and transmits
the result. Received data is decrypted and verified, reassembled, the result. Received data is decrypted and verified, reassembled,
and then delivered to higher-level clients. and then delivered to higher-level clients.
TLS records are typed, which allows multiple higher level protocols TLS records are typed, which allows multiple higher level protocols
to be multiplexed over the same record layer. This document to be multiplexed over the same record layer. This document
specifies three content types: handshake, application data, and specifies three content types: handshake, application data, and
alert. Implementations MUST NOT send record types not defined in alert. Implementations MUST NOT send record types not defined in
this document unless negotiated by some extension. If a TLS this document unless negotiated by some extension. If a TLS
implementation receives an unexpected record type, it MUST send an implementation receives an unexpected record type, it MUST terminate
"unexpected_message" alert. New record content type values are the connection with an "unexpected_message" alert. New record
assigned by IANA in the TLS Content Type Registry as described in content type values are assigned by IANA in the TLS Content Type
Section 10. Registry as described in Section 10.
Application data messages are carried by the record layer and are Application data messages are carried by the record layer and are
fragmented and encrypted as described below. The messages are fragmented and encrypted as described below. The messages are
treated as transparent data to the record layer. treated as transparent data to the record layer.
5.1. Record Layer 5.1. 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.
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records carrying data in chunks of 2^14 bytes or less. Message records carrying data in chunks of 2^14 bytes or less. Message
boundaries are not preserved in the record layer (i.e., multiple boundaries are not preserved in the record layer (i.e., multiple
messages of the same ContentType MAY be coalesced into a single messages of the same ContentType MAY be coalesced into a single
TLSPlaintext record, or a single message MAY be fragmented across TLSPlaintext record, or a single message MAY be fragmented across
several records). Alert messages (Section 6) MUST NOT be fragmented several records). Alert messages (Section 6) MUST NOT be fragmented
across records. across records.
enum { enum {
alert(21), alert(21),
handshake(22), handshake(22),
application_data(23) application_data(23),
(255) (255)
} ContentType; } ContentType;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */ ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */
uint16 length; uint16 length;
opaque fragment[TLSPlaintext.length]; opaque fragment[TLSPlaintext.length];
} TLSPlaintext; } TLSPlaintext;
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plaintext header followed by an encrypted body, which itself contains plaintext header followed by an encrypted body, which itself contains
a type and optional padding. a type and optional padding.
struct { struct {
opaque content[TLSPlaintext.length]; opaque content[TLSPlaintext.length];
ContentType type; ContentType type;
uint8 zeros[length_of_padding]; uint8 zeros[length_of_padding];
} TLSInnerPlaintext; } TLSInnerPlaintext;
struct { struct {
ContentType opaque_type = application_data(23); /* see fragment.type */ ContentType opaque_type = application_data(23); /* see TLSInnerPlaintext.type */
ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */ ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */
uint16 length; uint16 length;
opaque encrypted_record[length]; opaque encrypted_record[length];
} TLSCiphertext; } TLSCiphertext;
content The cleartext of TLSPlaintext.fragment. content The cleartext of TLSPlaintext.fragment.
type The content type of the record. type The content type of the record.
zeros An arbitrary-length run of zero-valued bytes may appear in the zeros An arbitrary-length run of zero-valued bytes may appear in the
cleartext after the type field. This provides an opportunity for cleartext after the type field. This provides an opportunity for
senders to pad any TLS record by a chosen amount as long as the senders to pad any TLS record by a chosen amount as long as the
total stays within record size limits. See Section 5.4 for more total stays within record size limits. See Section 5.4 for more
details. details.
opaque_type The outer opaque_type field of a TLSCiphertext record is opaque_type The outer opaque_type field of a TLSCiphertext record is
always set to the value 23 (application_data) for outward always set to the value 23 (application_data) for outward
compatibility with middleboxes accustomed to parsing previous compatibility with middleboxes accustomed to parsing previous
versions of TLS. The actual content type of the record is found versions of TLS. The actual content type of the record is found
in fragment.type after decryption. in TLSInnerPlaintext.type after decryption.
legacy_record_version The legacy_record_version field is identical legacy_record_version The legacy_record_version field is identical
to TLSPlaintext.legacy_record_version and is always { 3, 1 }. to TLSPlaintext.legacy_record_version and is always { 3, 1 }.
Note that the handshake protocol including the ClientHello and Note that the handshake protocol including the ClientHello and
ServerHello messages authenticates the protocol version, so this ServerHello messages authenticates the protocol version, so this
value is redundant. value is redundant.
length The length (in bytes) of the following length The length (in bytes) of the following
TLSCiphertext.fragment, which is the sum of the lengths of the TLSCiphertext.fragment, which is the sum of the lengths of the
content and the padding, plus one for the inner content type. The content and the padding, plus one for the inner content type. The
length MUST NOT exceed 2^14 + 256. An endpoint that receives a length MUST NOT exceed 2^14 + 256. An endpoint that receives a
record that exceeds this length MUST generate a fatal record that exceeds this length MUST terminate the connection with
"record_overflow" alert. a "record_overflow" alert.
encrypted_record The AEAD encrypted form of the serialized encrypted_record The AEAD encrypted form of the serialized
TLSInnerPlaintext structure. TLSInnerPlaintext structure.
AEAD ciphers take as input a single key, a nonce, a plaintext, and AEAD algorithms take as input a single key, a nonce, a plaintext, and
"additional data" to be included in the authentication check, as "additional data" to be included in the authentication check, as
described in Section 2.1 of [RFC5116]. The key is either the described in Section 2.1 of [RFC5116]. The key is either the
client_write_key or the server_write_key, the nonce is derived from client_write_key or the server_write_key, the nonce is derived from
the sequence number (see Section 5.3) and the client_write_iv or the sequence number (see Section 5.3) and the client_write_iv or
server_write_iv, and the additional data input is empty (zero server_write_iv, and the additional data input is empty (zero
length). Derivation of traffic keys is defined in Section 7.3. length). Derivation of traffic keys is defined in Section 7.3.
The plaintext is the concatenation of TLSPlaintext.fragment, The plaintext is the concatenation of TLSPlaintext.fragment,
TLSPlaintext.type, and any padding bytes (zeros). TLSPlaintext.type, and any padding bytes (zeros).
The AEAD output consists of the ciphertext output by the AEAD The AEAD output consists of the ciphertext output by the AEAD
encryption operation. The length of the plaintext is greater than encryption operation. The length of the plaintext is greater than
TLSPlaintext.length due to the inclusion of TLSPlaintext.type and TLSPlaintext.length due to the inclusion of TLSPlaintext.type and
however much padding is supplied by the sender. The length of the however much padding is supplied by the sender. The length of the
AEAD output will generally be larger than the plaintext, but by an AEAD output will generally be larger than the plaintext, but by an
amount that varies with the AEAD cipher. Since the ciphers might amount that varies with the AEAD algorithm. Since the ciphers might
incorporate padding, the amount of overhead could vary with different incorporate padding, the amount of overhead could vary with different
lengths of plaintext. Symbolically, lengths of plaintext. Symbolically,
AEADEncrypted = AEADEncrypted =
AEAD-Encrypt(write_key, nonce, plaintext of fragment) AEAD-Encrypt(write_key, nonce, plaintext of fragment)
In order to decrypt and verify, the cipher takes as input the key, In order to decrypt and verify, the cipher takes as input the key,
nonce, and the AEADEncrypted value. The output is either the nonce, and the AEADEncrypted value. The output is either the
plaintext or an error indicating that the decryption failed. There plaintext or an error indicating that the decryption failed. There
is no separate integrity check. That is: is no separate integrity check. That is:
plaintext of fragment = plaintext of fragment =
AEAD-Decrypt(write_key, nonce, AEADEncrypted) AEAD-Decrypt(write_key, nonce, AEADEncrypted)
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AEAD-Encrypt(write_key, nonce, plaintext of fragment) AEAD-Encrypt(write_key, nonce, plaintext of fragment)
In order to decrypt and verify, the cipher takes as input the key, In order to decrypt and verify, the cipher takes as input the key,
nonce, and the AEADEncrypted value. The output is either the nonce, and the AEADEncrypted value. The output is either the
plaintext or an error indicating that the decryption failed. There plaintext or an error indicating that the decryption failed. There
is no separate integrity check. That is: is no separate integrity check. That is:
plaintext of fragment = plaintext of fragment =
AEAD-Decrypt(write_key, nonce, AEADEncrypted) AEAD-Decrypt(write_key, nonce, AEADEncrypted)
If the decryption fails, a fatal "bad_record_mac" alert MUST be If the decryption fails, the receiver MUST terminate the connection
generated. with a "bad_record_mac" alert.
An AEAD cipher MUST NOT produce an expansion of greater than 255 An AEAD algorithm used in TLS 1.3 MUST NOT produce an expansion of
bytes. An endpoint that receives a record from its peer with greater than 255 bytes. An endpoint that receives a record from its
TLSCipherText.length larger than 2^14 + 256 octets MUST generate a peer with TLSCipherText.length larger than 2^14 + 256 octets MUST
fatal "record_overflow" alert. This limit is derived from the terminate the connection with a "record_overflow" alert. This limit
maximum TLSPlaintext length of 2^14 octets + 1 octet for ContentType is derived from the maximum TLSPlaintext length of 2^14 octets + 1
+ the maximum AEAD expansion of 255 octets. octet for ContentType + the maximum AEAD expansion of 255 octets.
5.3. Per-Record Nonce 5.3. Per-Record Nonce
A 64-bit sequence number is maintained separately for reading and A 64-bit sequence number is maintained separately for reading and
writing records. Each sequence number is set to zero at the writing records. Each sequence number is set to zero at the
beginning of a connection and whenever the key is changed. beginning of a connection and whenever the key is changed.
The sequence number is incremented after reading or writing each The sequence number is incremented after reading or writing each
record. The first record transmitted under a particular set of record. The first record transmitted under a particular set of
traffic keys record key MUST use sequence number 0. traffic keys record key MUST use sequence number 0.
Sequence numbers do not wrap. If a TLS implementation would need to Sequence numbers do not wrap. If a TLS implementation would need to
wrap a sequence number, it MUST either rekey (Section 4.4.3) or wrap a sequence number, it MUST either rekey (Section 4.5.3) or
terminate the connection. terminate the connection.
The length of the per-record nonce (iv_length) is set to max(8 bytes, The length of the per-record nonce (iv_length) is set to max(8 bytes,
N_MIN) for the AEAD algorithm (see [RFC5116] Section 4). An AEAD N_MIN) for the AEAD algorithm (see [RFC5116] Section 4). An AEAD
algorithm where N_MAX is less than 8 bytes MUST NOT be used with TLS. algorithm where N_MAX is less than 8 bytes MUST NOT be used with TLS.
The per-record nonce for the AEAD construction is formed as follows: The per-record nonce for the AEAD construction is formed as follows:
1. The 64-bit record sequence number is padded to the left with 1. The 64-bit record sequence number is padded to the left with
zeroes to iv_length. zeroes to iv_length.
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All encrypted TLS records can be padded to inflate the size of the All encrypted TLS records can be padded to inflate the size of the
TLSCipherText. This allows the sender to hide the size of the TLSCipherText. This allows the sender to hide the size of the
traffic from an observer. traffic from an observer.
When generating a TLSCiphertext record, implementations MAY choose to When generating a TLSCiphertext record, implementations MAY choose to
pad. An unpadded record is just a record with a padding length of pad. An unpadded record is just a record with a padding length of
zero. Padding is a string of zero-valued bytes appended to the zero. Padding is a string of zero-valued bytes appended to the
ContentType field before encryption. Implementations MUST set the ContentType field before encryption. Implementations MUST set the
padding octets to all zeros before encrypting. padding octets to all zeros before encrypting.
Application Data records may contain a zero-length fragment.content Application Data records may contain a zero-length
if the sender desires. This permits generation of plausibly-sized TLSInnerPlaintext.content if the sender desires. This permits
cover traffic in contexts where the presence or absence of activity generation of plausibly-sized cover traffic in contexts where the
may be sensitive. Implementations MUST NOT send Handshake or Alert presence or absence of activity may be sensitive. Implementations
records that have a zero-length fragment.content. MUST NOT send Handshake or Alert records that have a zero-length
TLSInnerPlaintext.content.
The padding sent is automatically verified by the record protection The padding sent is automatically verified by the record protection
mechanism: Upon successful decryption of a TLSCiphertext.fragment, mechanism: Upon successful decryption of a TLSCiphertext.fragment,
the receiving implementation scans the field from the end toward the the receiving implementation scans the field from the end toward the
beginning until it finds a non-zero octet. This non-zero octet is beginning until it finds a non-zero octet. This non-zero octet is
the content type of the message. This padding scheme was selected the content type of the message. This padding scheme was selected
because it allows padding of any encrypted TLS record by an arbitrary because it allows padding of any encrypted TLS record by an arbitrary
size (from zero up to TLS record size limits) without introducing new size (from zero up to TLS record size limits) without introducing new
content types. The design also enforces all-zero padding octets, content types. The design also enforces all-zero padding octets,
which allows for quick detection of padding errors. which allows for quick detection of padding errors.
Implementations MUST limit their scanning to the cleartext returned Implementations MUST limit their scanning to the cleartext returned
from the AEAD decryption. If a receiving implementation does not from the AEAD decryption. If a receiving implementation does not
find a non-zero octet in the cleartext, it should treat the record as find a non-zero octet in the cleartext, it MUST terminate the
having an unexpected ContentType, sending an "unexpected_message" connection with an "unexpected_message" alert.
alert.
The presence of padding does not change the overall record size The presence of padding does not change the overall record size
limitations - the full fragment plaintext may not exceed 2^14 octets. limitations - the full fragment plaintext may not exceed 2^14 octets.
Selecting a padding policy that suggests when and how much to pad is Selecting a padding policy that suggests when and how much to pad is
a complex topic, and is beyond the scope of this specification. If a complex topic, and is beyond the scope of this specification. If
the application layer protocol atop TLS has its own padding padding, the application layer protocol atop TLS has its own padding, it may
it may be preferable to pad application_data TLS records within the be preferable to pad application_data TLS records within the
application layer. Padding for encrypted handshake and alert TLS application layer. Padding for encrypted handshake and alert TLS
records must still be handled at the TLS layer, though. Later records must still be handled at the TLS layer, though. Later
documents may define padding selection algorithms, or define a documents may define padding selection algorithms, or define a
padding policy request mechanism through TLS extensions or some other padding policy request mechanism through TLS extensions or some other
means. means.
5.5. Limits on Key Usage 5.5. Limits on Key Usage
There are cryptographic limits on the amount of plaintext which can There are cryptographic limits on the amount of plaintext which can
be safely encrypted under a given set of keys. [AEAD-LIMITS] be safely encrypted under a given set of keys. [AEAD-LIMITS]
provides an analysis of these limits under the assumption that the provides an analysis of these limits under the assumption that the
underlying primitive (AES or ChaCha20) has no weaknesses. underlying primitive (AES or ChaCha20) has no weaknesses.
Implementations SHOULD do a key update Section 4.4.3 prior to Implementations SHOULD do a key update Section 4.5.3 prior to
reaching these limits. reaching these limits.
For AES-GCM, up to 2^24.5 full-size records may be encrypted on a For AES-GCM, up to 2^24.5 full-size records (about 24 million) may be
given connection while keeping a safety margin of approximately 2^-57 encrypted on a given connection while keeping a safety margin of
for Authenticated Encryption (AE) security. For ChaCha20/Poly1305, approximately 2^-57 for Authenticated Encryption (AE) security. For
the record sequence number will wrap before the safety limit is ChaCha20/Poly1305, the record sequence number would wrap before the
reached. safety limit is reached.
6. Alert Protocol 6. Alert Protocol
One of the content types supported by the TLS record layer is the One of the content types supported by the TLS record layer is the
alert type. Like other messages, alert messages are encrypted as alert type. Like other messages, alert messages are encrypted as
specified by the current connection state. specified by the current connection state.
Alert messages convey the severity of the message (warning or fatal) Alert messages convey the severity of the message (warning or fatal)
and a description of the alert. Warning-level messages are used to and a description of the alert. Warning-level messages are used to
indicate orderly closure of the connection (see Section 6.1). Upon indicate orderly closure of the connection (see Section 6.1). Upon
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internal_error(80), internal_error(80),
inappropriate_fallback(86), inappropriate_fallback(86),
user_canceled(90), user_canceled(90),
missing_extension(109), missing_extension(109),
unsupported_extension(110), unsupported_extension(110),
certificate_unobtainable(111), certificate_unobtainable(111),
unrecognized_name(112), unrecognized_name(112),
bad_certificate_status_response(113), bad_certificate_status_response(113),
bad_certificate_hash_value(114), bad_certificate_hash_value(114),
unknown_psk_identity(115), unknown_psk_identity(115),
certificate_required(116),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
6.1. Closure Alerts 6.1. Closure Alerts
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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.
6.2. Error Alerts 6.2. 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 its peer. error is detected, the detecting party sends a message to its peer.
Upon transmission or receipt of a fatal alert message, both parties Upon transmission or receipt of a fatal alert message, both parties
immediately close the connection. Whenever an implementation immediately close the connection.
encounters a condition which is defined as a fatal alert, it MUST
send the appropriate alert prior to closing the connection. All Whenever an implementation encounters a fatal error condition, it
alerts defined in this section below, as well as all unknown alerts SHOULD send an appropriate fatal alert and MUST close the connection
are universally considered fatal as of TLS 1.3 (see Section 6). without sending or receiving any additional data. In the rest of
this specification, the phrase "{terminate the connection, abort the
handshake}" is used without a specific alert means that the
implementation SHOULD send the alert indicated by the descriptions
below. The phrase "{terminate the connection, abort the handshake}
with a X alert" MUST send alert X if it sends any alert. All alerts
defined in this section below, as well as all unknown alerts are
universally considered fatal as of TLS 1.3 (see Section 6).
The following error alerts are defined: The following error alerts are defined:
unexpected_message An inappropriate message was received. This unexpected_message An inappropriate message (e.g., the wrong
alert should never be observed in communication between proper handshake message, premature application data, etc.) was received.
implementations. This alert should never be observed in communication between
proper implementations.
bad_record_mac This alert is returned if a record is received which bad_record_mac This alert is returned if a record is received which
cannot be deprotected. Because AEAD algorithms combine decryption cannot be deprotected. Because AEAD algorithms combine decryption
and verification, this alert is used for all deprotection and verification, this alert is used for all deprotection
failures. This alert should never be observed in communication failures. This alert should never be observed in communication
between proper implementations, except when messages were between proper implementations, except when messages were
corrupted in the network. corrupted in the network.
record_overflow A TLSCiphertext record was received that had a record_overflow A TLSCiphertext record was received that had a
length more than 2^14 + 256 bytes, or a record decrypted to a length more than 2^14 + 256 bytes, or a record decrypted to a
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unsupported_certificate A certificate was of an unsupported type. unsupported_certificate A certificate was of an unsupported type.
certificate_revoked A certificate was revoked by its signer. certificate_revoked A certificate was revoked by its signer.
certificate_expired A certificate has expired or is not currently certificate_expired A certificate has expired or is not currently
valid. valid.
certificate_unknown Some other (unspecified) issue arose in certificate_unknown Some other (unspecified) issue arose in
processing the certificate, rendering it unacceptable. processing the certificate, rendering it unacceptable.
illegal_parameter A field in the handshake was out of range or illegal_parameter A field in the handshake was incorrect or
inconsistent with other fields. inconsistent with other fields. This alert is used for errors
which conform to the formal protocol syntax but are otherwise
incorrect.
unknown_ca A valid certificate chain or partial chain was received, unknown_ca A valid certificate chain or partial chain was received,
but the certificate was not accepted because the CA certificate but the certificate was not accepted because the CA certificate
could not be located or couldn't be matched with a known, trusted could not be located or couldn't be matched with a known, trusted
CA. CA.
access_denied A valid certificate or PSK was received, but when access_denied A valid certificate or PSK was received, but when
access control was applied, the sender decided not to proceed with access control was applied, the sender decided not to proceed with
negotiation. negotiation.
decode_error A message could not be decoded because some field was decode_error A message could not be decoded because some field was
out of the specified range or the length of the message was out of the specified range or the length of the message was
incorrect. This alert should never be observed in communication incorrect. This alert is used for errors where the message does
between proper implementations, except when messages were not conform to the formal protocol syntax. This alert should
corrupted in the network. never be observed in communication between proper implementations,
except when messages were corrupted in the network.
decrypt_error A handshake cryptographic operation failed, including decrypt_error A handshake cryptographic operation failed, including
being unable to correctly verify a signature or validate a being unable to correctly verify a signature or validate a
Finished message. Finished message.
protocol_version The protocol version the peer has attempted to protocol_version The protocol version the peer has attempted to
negotiate is recognized but not supported. (see Appendix C) negotiate is recognized but not supported. (see Appendix C)
insufficient_security Returned instead of "handshake_failure" when a insufficient_security Returned instead of "handshake_failure" when a
negotiation has failed specifically because the server requires negotiation has failed specifically because the server requires
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internal_error An internal error unrelated to the peer or the internal_error An internal error unrelated to the peer or the
correctness of the protocol (such as a memory allocation failure) correctness of the protocol (such as a memory allocation failure)
makes it impossible to continue. makes it impossible to continue.
inappropriate_fallback Sent by a server in response to an invalid inappropriate_fallback Sent by a server in response to an invalid
connection retry attempt from a client. (see [RFC7507]) connection retry attempt from a client. (see [RFC7507])
missing_extension Sent by endpoints that receive a hello message not missing_extension Sent by endpoints that receive a hello message not
containing an extension that is mandatory to send for the offered containing an extension that is mandatory to send for the offered
TLS version. [[TODO: IANA Considerations.]] TLS version or other negotiated parameters. [[TODO: IANA
Considerations.]]
unsupported_extension Sent by endpoints receiving any hello message unsupported_extension Sent by endpoints receiving any hello message
containing an extension known to be prohibited for inclusion in containing an extension known to be prohibited for inclusion in
the given hello message, including any extensions in a ServerHello the given hello message, including any extensions in a ServerHello
not first offered in the corresponding ClientHello. not first offered in the corresponding ClientHello.
certificate_unobtainable Sent by servers when unable to obtain a certificate_unobtainable Sent by servers when unable to obtain a
certificate from a URL provided by the client via the certificate from a URL provided by the client via the
"client_certificate_url" extension [RFC6066]. "client_certificate_url" extension [RFC6066].
unrecognized_name Sent by servers when no server exists identified unrecognized_name Sent by servers when no server exists identified
by the name provided by the client via the "server_name" extension by the name provided by the client via the "server_name" extension
[RFC6066]. [RFC6066].
bad_certificate_status_response Sent by clients when an invalid or bad_certificate_status_response Sent by clients when an invalid or
unacceptable OCSP response is provided by the server via the unacceptable OCSP response is provided by the server via the
"status_request" extension [RFC6066]. This alert is always fatal. "status_request" extension [RFC6066].
bad_certificate_hash_value Sent by servers when a retrieved object bad_certificate_hash_value Sent by servers when a retrieved object
does not have the correct hash provided by the client via the does not have the correct hash provided by the client via the
"client_certificate_url" extension [RFC6066]. "client_certificate_url" extension [RFC6066].
unknown_psk_identity Sent by servers when PSK key establishment is unknown_psk_identity Sent by servers when PSK key establishment is
desired but no acceptable PSK identity is provided by the client. desired but no acceptable PSK identity is provided by the client.
Sending this alert is OPTIONAL; servers MAY instead choose to send Sending this alert is OPTIONAL; servers MAY instead choose to send
a "decrypt_error" alert to merely indicate an invalid PSK a "decrypt_error" alert to merely indicate an invalid PSK
identity. identity.
certificate_required Sent by servers when a client certificate is
desired but none was provided by the client.
[[TODO: IANA Considerations for new alert values.]]
New Alert values are assigned by IANA as described in Section 10. New Alert values are assigned by IANA as described in Section 10.
7. Cryptographic Computations 7. 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 client and server random values.
7.1. Key Schedule 7.1. Key Schedule
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combined to create the actual working keying material, as detailed combined to create the actual working keying material, as detailed
below. The key derivation process makes use of the HKDF-Extract and below. The key derivation process makes use of the HKDF-Extract and
HKDF-Expand functions as defined for HKDF [RFC5869], as well as the HKDF-Expand functions as defined for HKDF [RFC5869], as well as the
functions defined below: functions defined below:
HKDF-Expand-Label(Secret, Label, HashValue, Length) = HKDF-Expand-Label(Secret, Label, HashValue, Length) =
HKDF-Expand(Secret, HkdfLabel, Length) HKDF-Expand(Secret, HkdfLabel, Length)
Where HkdfLabel is specified as: Where HkdfLabel is specified as:
struct HkdfLabel struct {
{ uint16 length = Length;
uint16 length = Length; opaque label<9..255> = "TLS 1.3, " + Label;
opaque label<9..255> = "TLS 1.3, " + Label; opaque hash_value<0..255> = HashValue;
opaque hash_value<0..255> = HashValue; } HkdfLabel;
};
Derive-Secret(Secret, Label, Messages) = Derive-Secret(Secret, Label, Messages) =
HKDF-Expand-Label(Secret, Label, HKDF-Expand-Label(Secret, Label,
Hash(Messages) + Hash(Messages) +
Hash(resumption_context), Hash.Length) Hash(resumption_context), Hash.length)
The Hash function and the HKDF hash are the cipher suite hash The Hash function and the HKDF hash are the cipher suite hash
function. Hash.Length is its output length. algorithm. Hash.length is its output length.
Given a set of n InputSecrets, the final "master secret" is computed Given a set of n InputSecrets, the final "master secret" is computed
by iteratively invoking HKDF-Extract with InputSecret_1, by iteratively invoking HKDF-Extract with InputSecret_1,
InputSecret_2, etc. The initial secret is simply a string of zeroes InputSecret_2, etc. The initial secret is simply a string of zeroes
as long as the size of the Hash that is the basis for the HKDF. as long as the size of the Hash that is the basis for the HKDF.
Concretely, for the present version of TLS 1.3, secrets are added in Concretely, for the present version of TLS 1.3, secrets are added in
the following order: the following order:
- PSK - PSK
- (EC)DHE shared secret - (EC)DHE shared secret
This produces a full key derivation schedule shown in the diagram This produces a full key derivation schedule shown in the diagram
below. In this diagram, the following formatting conventions apply: below. In this diagram, the following formatting conventions apply:
- HKDF-Extract is drawn as taking the Salt argument from the top and - HKDF-Extract is drawn as taking the Salt argument from the top and
the IKM argument from the left. the IKM argument from the left.
- Derive-Secret's Secret argument is indicated by the arrow coming - Derive-Secret's Secret argument is indicated by the arrow coming
in from the left. For instance, the Early Secret is the Secret in from the left. For instance, the Early Secret is the Secret
for generating the early_traffic_secret. for generating the client_early_traffic_secret.
Note that the 0-RTT Finished message is not included in the Derive- Note that the 0-RTT Finished message is not included in the Derive-
Secret operation. Secret operation.
0 0
| |
v v
PSK -> HKDF-Extract PSK -> HKDF-Extract
| |
v v
Early Secret ---> Derive-Secret(., "early traffic secret", Early Secret ---> Derive-Secret(., "client early traffic secret",
| ClientHello) | ClientHello)
| = early_traffic_secret | = client_early_traffic_secret
v v
(EC)DHE -> HKDF-Extract (EC)DHE -> HKDF-Extract
| |
v v
Handshake Handshake Secret
Secret -----> Derive-Secret(., "handshake traffic secret", |
+---------> Derive-Secret(., "client handshake traffic secret",
| ClientHello...ServerHello) | ClientHello...ServerHello)
| = handshake_traffic_secret | = client_handshake_traffic_secret
|
+---------> Derive-Secret(., "server handshake traffic secret",
| ClientHello...ServerHello)
| = server_handshake_traffic_secret
|
v v
0 -> HKDF-Extract 0 -> HKDF-Extract
| |
v v
Master Secret Master Secret
| |
+---------> Derive-Secret(., "application traffic secret", +---------> Derive-Secret(., "client application traffic secret",
| ClientHello...Server Finished) | ClientHello...Server Finished)
| = traffic_secret_0 | = client_traffic_secret_0
|
+---------> Derive-Secret(., "server application traffic secret",
| ClientHello...Server Finished)
| = server_traffic_secret_0
| |
+---------> Derive-Secret(., "exporter master secret", +---------> Derive-Secret(., "exporter master secret",
| ClientHello...Client Finished) | ClientHello...Client Finished)
| = exporter_secret | = exporter_secret
| |
+---------> Derive-Secret(., "resumption master secret", +---------> Derive-Secret(., "resumption master secret",
ClientHello...Client Finished) ClientHello...Client Finished)
= resumption_secret = resumption_secret
The general pattern here is that the secrets shown down the left side The general pattern here is that the secrets shown down the left side
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If a given secret is not available, then the 0-value consisting of a If a given secret is not available, then the 0-value consisting of a
string of Hash.length zeroes is used. Note that this does not mean string of Hash.length zeroes is used. Note that this does not mean
skipping rounds, so if PSK is not in use Early Secret will still be skipping rounds, so if PSK is not in use Early Secret will still be
HKDF-Extract(0, 0). HKDF-Extract(0, 0).
7.2. Updating Traffic Keys and IVs 7.2. Updating Traffic Keys and IVs
Once the handshake is complete, it is possible for either side to Once the handshake is complete, it is possible for either side to
update its sending traffic keys using the KeyUpdate handshake message update its sending traffic keys using the KeyUpdate handshake message
defined in Section 4.4.3. The next generation of traffic keys is defined in Section 4.5.3. The next generation of traffic keys is
computed by generating traffic_secret_N+1 from traffic_secret_N as computed by generating client_/server_traffic_secret_N+1 from
described in this section then re-deriving the traffic keys as client_/server_traffic_secret_N as described in this section then re-
described in Section 7.3. deriving the traffic keys as described in Section 7.3.
The next-generation traffic_secret is computed as: The next-generation traffic_secret is computed as:
traffic_secret_N+1 = HKDF-Expand-Label( traffic_secret_N+1 = HKDF-Expand-Label(
traffic_secret_N, traffic_secret_N,
"application traffic secret", "", Hash.Length) "application traffic secret", "", Hash.length)
Once traffic_secret_N+1 and its associated traffic keys have been Once client/server_traffic_secret_N+1 and its associated traffic keys
computed, implementations SHOULD delete traffic_secret_N. Once the have been computed, implementations SHOULD delete client_/
directional keys are no longer needed, they SHOULD be deleted as server_traffic_secret_N and its associated traffic keys.
well.
7.3. Traffic Key Calculation 7.3. Traffic Key Calculation
The traffic keying material is generated from the following input The traffic keying material is generated from the following input
values: values:
- A secret value - A secret value
- A phase value indicating the phase of the protocol the keys are - A phase value indicating the phase of the protocol the keys are
being generated for being generated for
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The keying material is computed using: The keying material is computed using:
key = HKDF-Expand-Label(Secret, key = HKDF-Expand-Label(Secret,
phase + ", " + purpose, phase + ", " + purpose,
"", "",
key_length) key_length)
The following table describes the inputs to the key calculation for The following table describes the inputs to the key calculation for
each class of traffic keys: each class of traffic keys:
+-------------+--------------------------+--------------------------+ +-------------+-----------------------------------+-----------------+
| Record Type | Secret | Phase | | Record Type | Secret | Phase |
+-------------+--------------------------+--------------------------+ +-------------+-----------------------------------+-----------------+
| 0-RTT | early_traffic_secret | "early handshake key | | 0-RTT | client_early_traffic_secret | "early |
| Handshake | | expansion" | | Handshake | | handshake key |
| | | | | | | expansion" |
| 0-RTT | early_traffic_secret | "early application data | | | | |
| Application | | key expansion" | | 0-RTT | client_early_traffic_secret | "early |
| | | | | Application | | application |
| Handshake | handshake_traffic_secret | "handshake key | | | | data key |
| | | expansion" | | | | expansion" |
| | | | | | | |
| Application | traffic_secret_N | "application data key | | Handshake | [sender]_handshake_traffic_secret | "handshake key |
| Data | | expansion" | | | | expansion" |
+-------------+--------------------------+--------------------------+ | | | |
| Application | [sender]_traffic_secret_N | "application |
| Data | | data key |
| | | expansion" |
+-------------+-----------------------------------+-----------------+
The following table indicates the purpose values for each type of The [sender] in this table denotes the sending side. The following
key: table indicates the purpose values for each type of key:
+------------------+--------------------+ +----------+---------+
| Key Type | Purpose | | Key Type | Purpose |
+------------------+--------------------+ +----------+---------+
| client_write_key | "client write key" | | key | "key" |
| | | | | |
| server_write_key | "server write key" | | iv | "iv" |
| | | +----------+---------+
| client_write_iv | "client write iv" |
| | |
| server_write_iv | "server write iv" |
+------------------+--------------------+
All the traffic keying material is recomputed whenever the underlying All the traffic keying material is recomputed whenever the underlying
Secret changes (e.g., when changing from the handshake to application Secret changes (e.g., when changing from the handshake to application
data keys or upon a key update). data keys or upon a key update).
7.3.1. Diffie-Hellman 7.3.1. Diffie-Hellman
A conventional Diffie-Hellman computation is performed. The A conventional Diffie-Hellman computation is performed. The
negotiated key (Z) is converted to byte string by encoding in big- negotiated key (Z) is converted to byte string by encoding in big-
endian, padded with zeros up to the size of the prime. This byte endian, padded with zeros up to the size of the prime. This byte
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the secret key (into scalar input) and the peer's public key (into the secret key (into scalar input) and the peer's public key (into
u-coordinate point input). The output is used raw, with no u-coordinate point input). The output is used raw, with no
processing. processing.
For X25519 and X448, see [RFC7748]. For X25519 and X448, see [RFC7748].
7.3.3. Exporters 7.3.3. Exporters
[RFC5705] defines keying material exporters for TLS in terms of the [RFC5705] defines keying material exporters for TLS in terms of the
TLS PRF. This document replaces the PRF with HKDF, thus requiring a TLS PRF. This document replaces the PRF with HKDF, thus requiring a
new construction. The exporter interface remains the same, however new construction. The exporter interface remains the same. If
the value is computed as: context is provided, the value is computed as:
HKDF-Expand-Label(exporter_secret, HKDF-Expand-Label(exporter_secret, label, context_value, key_length)
label, context_value, key_length)
If no context is provided, the value is computed as:
HKDF-Expand-Label(exporter_secret, label, "", key_length)
Note that providing no context computes the same value as providing
an empty context. As of this document's publication, no allocated
exporter label is used with both modes. Future specifications MUST
NOT provide an empty context and no context with the same label and
SHOULD provide a context, possibly empty, in all exporter
computations.
8. Compliance Requirements 8. Compliance Requirements
8.1. MTI Cipher Suites 8.1. MTI 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 otherwise, a TLS-compliant application MUST implement the
TLS_AES_128_GCM_SHA256 cipher suite and SHOULD implement the TLS_AES_128_GCM_SHA256 cipher suite and SHOULD implement the
TLS_AES_256_GCM_SHA384 and TLS_CHACHA20_POLY1305_SHA256 cipher TLS_AES_256_GCM_SHA384 and TLS_CHACHA20_POLY1305_SHA256 cipher
suites. suites.
A TLS-compliant application MUST support digital signatures with A TLS-compliant application MUST support digital signatures with
rsa_pkcs1_sha256 (for certificates), rsa_pss_sha256 (for rsa_pkcs1_sha256 (for certificates), rsa_pss_sha256 (for
skipping to change at page 76, line 24 skipping to change at page 78, line 36
CertificateVerify and certificates), and ecdsa_secp256r1_sha256. A CertificateVerify and certificates), and ecdsa_secp256r1_sha256. A
TLS-compliant application MUST support key exchange with secp256r1 TLS-compliant application MUST support key exchange with secp256r1
(NIST P-256) and SHOULD support key exchange with X25519 [RFC7748]. (NIST P-256) and SHOULD support key exchange with X25519 [RFC7748].
8.2. MTI Extensions 8.2. MTI Extensions
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 following otherwise, a TLS-compliant application MUST implement the following
TLS extensions: TLS extensions:
- Signature Algorithms ("signature_algorithms"; Section 4.2.2) - Supported Versions ("supported_versions"; Section 4.2.1)
- Negotiated Groups ("supported_groups"; Section 4.2.3) - Signature Algorithms ("signature_algorithms"; Section 4.2.3)
- Key Share ("key_share"; Section 4.2.4) - Negotiated Groups ("supported_groups"; Section 4.2.4)
- Pre-Shared Key ("pre_shared_key"; Section 4.2.5) - Key Share ("key_share"; Section 4.2.5)
- Pre-Shared Key ("pre_shared_key"; Section 4.2.6)
- Server Name Indication ("server_name"; Section 3 of [RFC6066]) - Server Name Indication ("server_name"; Section 3 of [RFC6066])
- Cookie ("cookie"; Section 4.2.1) - Cookie ("cookie"; Section 4.2.2)
All implementations MUST send and use these extensions when offering All implementations MUST send and use these extensions when offering
applicable cipher suites: applicable cipher suites:
- "supported_versions" is REQUIRED for all ClientHello messages.
- "signature_algorithms" is REQUIRED for certificate authenticated - "signature_algorithms" is REQUIRED for certificate authenticated
cipher suites. cipher suites.
- "supported_groups" and "key_share" are REQUIRED for DHE or ECDHE - "supported_groups" and "key_share" are REQUIRED for DHE or ECDHE
cipher suites. cipher suites.
- "pre_shared_key" is REQUIRED for PSK cipher suites. - "pre_shared_key" is REQUIRED for PSK cipher suites.
- "cookie" is REQUIRED for all cipher suites. - "cookie" is REQUIRED for all cipher suites.
When negotiating use of applicable cipher suites, endpoints MUST When negotiating use of applicable cipher suites, endpoints MUST
abort the connection with a "missing_extension" alert if the required abort the handshake with a "missing_extension" alert if the required
extension was not provided. Any endpoint that receives any invalid extension was not provided. Any endpoint that receives any invalid
combination of cipher suites and extensions MAY abort the connection combination of cipher suites and extensions MAY abort the connection
with a "missing_extension" alert, regardless of negotiated with a "missing_extension" alert, regardless of negotiated
parameters. parameters.
Additionally, all implementations MUST support use of the Additionally, all implementations MUST support use of the
"server_name" extension with applications capable of using it. "server_name" extension with applications capable of using it.
Servers MAY require clients to send a valid "server_name" extension. Servers MAY require clients to send a valid "server_name" extension.
Servers requiring this extension SHOULD respond to a ClientHello Servers requiring this extension SHOULD respond to a ClientHello
lacking a "server_name" extension with a fatal "missing_extension" lacking a "server_name" extension by terminating the connection with
alert. a "missing_extension" alert.
Servers MUST NOT send the "signature_algorithms" extension; if a
client receives this extension it MUST respond with a fatal
"unsupported_extension" alert and close the connection.
9. Security Considerations 9. Security Considerations
Security issues are discussed throughout this memo, especially in Security issues are discussed throughout this memo, especially in
Appendices B, C, and D. Appendices B, C, and D.
10. IANA Considerations 10. IANA Considerations
This document uses several registries that were originally created in This document uses several registries that were originally created in
[RFC4346]. IANA has updated these to reference this document. The [RFC4346]. IANA has updated these to reference this document. The
registries and their allocation policies are below: registries and their allocation policies are below:
- TLS Cipher Suite Registry: Values with the first byte in the range - TLS Cipher Suite Registry: Values with the first byte in the range
0-254 (decimal) are assigned via Specification Required [RFC2434]. 0-254 (decimal) are assigned via Specification Required [RFC2434].
Values with the first byte 255 (decimal) are reserved for Private Values with the first byte 255 (decimal) are reserved for Private
Use [RFC2434]. IANA [SHALL add/has added] a "Recommended" column Use [RFC2434].
to the cipher suite registry. All cipher suites listed in
Appendix A.4 are marked as "Yes". All other cipher suites are
marked as "No". IANA [SHALL add/has added] add a note to this
column reading:
Cipher suites marked as "Yes" are those allocated via Standards IANA [SHALL add/has added] the cipher suites listed in
Track RFCs. Cipher suites marked as "No" are not; cipher Appendix A.4 to the registry. The "Value" and "Description"
suites marked "No" range from "good" to "bad" from a columns are taken from the table. The "DTLS-OK" and "Recommended"
cryptographic standpoint. columns are both marked as "Yes" for each new cipher suite.
[[This assumes [I-D.sandj-tls-iana-registry-updates] has been
applied.]]
- TLS ContentType Registry: Future values are allocated via - TLS ContentType Registry: Future values are allocated via
Standards Action [RFC2434]. Standards Action [RFC2434].
- TLS Alert Registry: Future values are allocated via Standards - TLS Alert Registry: Future values are allocated via Standards
Action [RFC2434]. Action [RFC2434].
- TLS HandshakeType Registry: Future values are allocated via - TLS HandshakeType Registry: Future values are allocated via
Standards Action [RFC2434]. IANA [SHALL update/has updated] this Standards Action [RFC2434]. IANA [SHALL update/has updated] this
registry to rename item 4 from "NewSessionTicket" to registry to rename item 4 from "NewSessionTicket" to
skipping to change at page 78, line 18 skipping to change at page 80, line 27
IANA has updated it to reference this document. The registry and its IANA has updated it to reference this document. The registry and its
allocation policy is listed below: allocation policy is listed below:
- TLS ExtensionType Registry: Values with the first byte in the - TLS ExtensionType Registry: Values with the first byte in the
range 0-254 (decimal) are assigned via Specification Required range 0-254 (decimal) are assigned via Specification Required
[RFC2434]. Values with the first byte 255 (decimal) are reserved [RFC2434]. Values with the first byte 255 (decimal) are reserved
for Private Use [RFC2434]. IANA [SHALL update/has updated] this for Private Use [RFC2434]. IANA [SHALL update/has updated] this
registry to include the "key_share", "pre_shared_key", and registry to include the "key_share", "pre_shared_key", and
"early_data" extensions as defined in this document. "early_data" extensions as defined in this document.
IANA [shall update/has updated] this registry to add a
"Recommended" column. IANA [shall/has] initially populated this
column with the values in the table below. This table has been
generated by marking Standards Track RFCs as "Yes" and all others
as "No".
IANA [shall update/has updated] this registry to include a "TLS IANA [shall update/has updated] this registry to include a "TLS
1.3" column with the following four values: "Client", indicating 1.3" column with the following four values: "Client", indicating
that the server shall not send them. "Clear", indicating that that the server shall not send them. "Clear", indicating that
they shall be in the ServerHello. "Encrypted", indicating that they shall be in the ServerHello. "Encrypted", indicating that
they shall be in the EncryptedExtensions block, and "No" they shall be in the EncryptedExtensions block, and "No"
indicating that they are not used in TLS 1.3. This column [shall indicating that they are not used in TLS 1.3. This column [shall
be/has been] initially populated with the values in this document. be/has been] initially populated with the values in this document.
IANA [shall update/has updated] this registry to add a
"Recommended" column. IANA [shall/has] initially populated this
column with the values in the table below. This table has been
generated by marking Standards Track RFCs as "Yes" and all others
as "No".
+-------------------------------+-----------+-----------------------+ IANA [shall update/has updated] this registry to include a
| Extension | Recommend | TLS 1.3 | "HelloRetryRequest" column with the following two values: "Yes",
| | ed | | indicating it may be sent in HelloRetryRequest, and "No",
+-------------------------------+-----------+-----------------------+ indicating it may not be sent in HelloRetryRequest. This column
| server_name [RFC6066] | Yes | Encrypted | [shall be/has been] initially populated with the values in this
| | | | document.
| max_fragment_length [RFC6066] | Yes | Encrypted |
| | | | +------------------------------+----------+---------+---------------+
| client_certificate_url | Yes | Encrypted | | Extension | Recommen | TLS 1.3 | HelloRetryReq |
| [RFC6066] | | | | | ded | | uest |
| | | | +------------------------------+----------+---------+---------------+
| trusted_ca_keys [RFC6066] | Yes | Encrypted | | server_name [RFC6066] | Yes | Encrypt | No |
| | | | | | | ed | |
| truncated_hmac [RFC6066] | Yes | No | | | | | |
| | | | | max_fragment_length | Yes | Encrypt | No |
| status_request [RFC6066] | Yes | Encrypted | | [RFC6066] | | ed | |
| | | | | | | | |
| user_mapping [RFC4681] | Yes | Encrypted | | client_certificate_url | Yes | Encrypt | No |
| | | | | [RFC6066] | | ed | |
| client_authz [RFC5878] | No | Encrypted | | | | | |
| | | | | trusted_ca_keys [RFC6066] | Yes | Encrypt | No |
| server_authz [RFC5878] | No | Encrypted | | | | ed | |
| | | | | | | | |
| cert_type [RFC6091] | Yes | Encrypted | | truncated_hmac [RFC6066] | Yes | No | No |
| | | | | | | | |
| supported_groups [RFC-ietf- | Yes | Encrypted | | status_request [RFC6066] | Yes | Encrypt | No |
| tls-negotiated-ff-dhe] | | | | | | ed | |
| | | | | | | | |
| ec_point_formats [RFC4492] | Yes | No | | user_mapping [RFC4681] | Yes | Encrypt | No |
| | | | | | | ed | |
| srp [RFC5054] | No | No | | | | | |
| | | | | client_authz [RFC5878] | No | No | No |
| signature_algorithms | Yes | Client | | | | | |
| [RFC5246] | | | | server_authz [RFC5878] | No | No | No |
| | | | | | | | |
| use_srtp [RFC5764] | Yes | Encrypted | | cert_type [RFC6091] | Yes | Encrypt | No |
| | | | | | | ed | |
| heartbeat [RFC6520] | Yes | Encrypted | | | | | |
| | | | | supported_groups [RFC7919] | Yes | Encrypt | No |
| application_layer_protocol_ne | Yes | Encrypted | | | | ed | |
| gotiation [RFC7301] | | | | | | | |
| | | | | ec_point_formats [RFC4492] | Yes | No | No |
| status_request_v2 [RFC6961] | Yes | Encrypted | | | | | |
| | | | | srp [RFC5054] | No | No | No |
| signed_certificate_timestamp | No | Encrypted | | | | | |
| [RFC6962] | | | | signature_algorithms | Yes | Clear | No |
| | | | | [RFC5246] | | | |
| client_certificate_type | Yes | Encrypted | | | | | |
| [RFC7250] | | | | use_srtp [RFC5764] | Yes | Encrypt | No |
| | | | | | | ed | |
| server_certificate_type | Yes | Encrypted | | | | | |
| [RFC7250] | | | | heartbeat [RFC6520] | Yes | Encrypt | No |
| | | | | | | ed | |
| padding [RFC7685] | Yes | Client | | | | | |
| | | | | application_layer_protocol_n | Yes | Encrypt | No |
| encrypt_then_mac [RFC7366] | Yes | No | | egotiation [RFC7301] | | ed | |
| | | | | | | | |
| extended_master_secret | Yes | No | | status_request_v2 [RFC6961] | Yes | Encrypt | No |
| [RFC7627] | | | | | | ed | |
| | | | | | | | |
| SessionTicket TLS [RFC4507] | Yes | No | | signed_certificate_timestamp | No | Encrypt | No |
| | | | | [RFC6962] | | ed | |
| renegotiation_info [RFC5746] | Yes | No | | | | | |
| | | | | client_certificate_type | Yes | Encrypt | No |
| key_share [[this document]] | Yes | Clear | | [RFC7250] | | ed | |
| | | | | | | | |
| pre_shared_key [[this | Yes | Clear | | server_certificate_type | Yes | Encrypt | No |
| document]] | | | | [RFC7250] | | ed | |
| | | | | | | | |
| early_data [[this document]] | Yes | Encrypted | | padding [RFC7685] | Yes | Client | No |
| | | | | | | | |
| cookie [[this document]] | Yes | Encrypted/HelloRetryR | | encrypt_then_mac [RFC7366] | Yes | No | No |
| | | equest | | | | | |
+-------------------------------+-----------+-----------------------+ | extended_master_secret | Yes | No | No |
| [RFC7627] | | | |
| | | | |
| SessionTicket TLS [RFC4507] | Yes | No | No |
| | | | |
| renegotiation_info [RFC5746] | Yes | No | No |
| | | | |
| key_share [[this document]] | Yes | Clear | Yes |
| | | | |
| pre_shared_key [[this | Yes | Clear | No |
| document]] | | | |
| | | | |
| early_data [[this document]] | Yes | Encrypt | No |
| | | ed | |
| | | | |
| cookie [[this document]] | Yes | Client | Yes |
| | | | |
| supported_versions [[this | Yes | Client | No |
| document]] | | | |
+------------------------------+----------+---------+---------------+
In addition, this document defines two new registries to be In addition, this document defines two new registries to be
maintained by IANA maintained by IANA
- TLS SignatureScheme Registry: Values with the first byte in the - TLS SignatureScheme Registry: Values with the first byte in the
range 0-254 (decimal) are assigned via Specification Required range 0-254 (decimal) are assigned via Specification Required
[RFC2434]. Values with the first byte 255 (decimal) are reserved [RFC2434]. Values with the first byte 255 (decimal) are reserved
for Private Use [RFC2434]. This registry SHALL have a for Private Use [RFC2434]. Values with the first byte in the
"Recommended" column. The registry [shall be/ has been] initially range 0-6 or with the second byte in the range 0-3 that are not
populated with the values described in Section 4.2.2. The currently allocated are reserved for backwards compatibility.
following values SHALL be marked as "Recommended": This registry SHALL have a "Recommended" column. The registry
ecdsa_secp256r1_sha256, ecdsa_secp384r1_sha384, rsa_pss_sha256, [shall be/ has been] initially populated with the values described
rsa_pss_sha384, rsa_pss_sha512, ed25519. in Section 4.2.3. The following values SHALL be marked as
"Recommended": ecdsa_secp256r1_sha256, ecdsa_secp384r1_sha384,
rsa_pss_sha256, rsa_pss_sha384, rsa_pss_sha512, ed25519.
Finally, this document obsoletes the TLS HashAlgorithm Registry and
the TLS SignatureAlgorithm Registry, both originally created in
[RFC5246]. IANA [SHALL update/has updated] the TLS HashAlgorithm
Registry to list values 7-223 as "Reserved" and the TLS
SignatureAlgorithm Registry to list values 4-233 as "Reserved".
11. References 11. References
11.1. Normative References 11.1. Normative References
[AES] National Institute of Standards and Technology, [AES] National Institute of Standards and Technology,
"Specification for the Advanced Encryption Standard "Specification for the Advanced Encryption Standard
(AES)", NIST FIPS 197, November 2001. (AES)", NIST FIPS 197, November 2001.
[DH] Diffie, W. and M. Hellman, "New Directions in [DH] Diffie, W. and M. Hellman, "New Directions in
Cryptography", IEEE Transactions on Information Theory, Cryptography", IEEE Transactions on Information Theory,
V.IT-22 n.6 , June 1977. V.IT-22 n.6 , June 1977.
[I-D.irtf-cfrg-eddsa] [I-D.irtf-cfrg-eddsa]
Josefsson, S. and I. Liusvaara, "Edwards-curve Digital Josefsson, S. and I. Liusvaara, "Edwards-curve Digital
Signature Algorithm (EdDSA)", draft-irtf-cfrg-eddsa-06 Signature Algorithm (EdDSA)", draft-irtf-cfrg-eddsa-08
(work in progress), August 2016. (work in progress), August 2016.
[I-D.mattsson-tls-ecdhe-psk-aead]
Mattsson, J. and D. Migault, "ECDHE_PSK with AES-GCM and
AES-CCM Cipher Suites for Transport Layer Security (TLS)",
draft-mattsson-tls-ecdhe-psk-aead-05 (work in progress),
April 2016.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997, DOI 10.17487/RFC2104, February 1997,
<http://www.rfc-editor.org/info/rfc2104>. <http://www.rfc-editor.org/info/rfc2104>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 82, line 46 skipping to change at page 85, line 21
CCM Elliptic Curve Cryptography (ECC) Cipher Suites for CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014, TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014,
<http://www.rfc-editor.org/info/rfc7251>. <http://www.rfc-editor.org/info/rfc7251>.
[RFC7443] Patil, P., Reddy, T., Salgueiro, G., and M. Petit- [RFC7443] Patil, P., Reddy, T., Salgueiro, G., and M. Petit-
Huguenin, "Application-Layer Protocol Negotiation (ALPN) Huguenin, "Application-Layer Protocol Negotiation (ALPN)
Labels for Session Traversal Utilities for NAT (STUN) Labels for Session Traversal Utilities for NAT (STUN)
Usages", RFC 7443, DOI 10.17487/RFC7443, January 2015, Usages", RFC 7443, DOI 10.17487/RFC7443, January 2015,
<http://www.rfc-editor.org/info/rfc7443>. <http://www.rfc-editor.org/info/rfc7443>.
[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<http://www.rfc-editor.org/info/rfc7539>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <http://www.rfc-editor.org/info/rfc7748>. 2016, <http://www.rfc-editor.org/info/rfc7748>.
[RFC7905] Langley, A., Chang, W., Mavrogiannopoulos, N., [RFC7905] Langley, A., Chang, W., Mavrogiannopoulos, N.,
Strombergson, J., and S. Josefsson, "ChaCha20-Poly1305 Strombergson, J., and S. Josefsson, "ChaCha20-Poly1305
Cipher Suites for Transport Layer Security (TLS)", Cipher Suites for Transport Layer Security (TLS)",
RFC 7905, DOI 10.17487/RFC7905, June 2016, RFC 7905, DOI 10.17487/RFC7905, June 2016,
<http://www.rfc-editor.org/info/rfc7905>. <http://www.rfc-editor.org/info/rfc7905>.
skipping to change at page 84, line 28 skipping to change at page 87, line 5
[FI06] Finney, H., "Bleichenbacher's RSA signature forgery based [FI06] Finney, H., "Bleichenbacher's RSA signature forgery based
on implementation error", August 2006, on implementation error", August 2006,
<https://www.ietf.org/mail-archive/web/openpgp/current/ <https://www.ietf.org/mail-archive/web/openpgp/current/
msg00999.html>. msg00999.html>.
[GCM] Dworkin, M., "Recommendation for Block Cipher Modes of [GCM] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Galois/Counter Mode (GCM) and GMAC", Operation: Galois/Counter Mode (GCM) and GMAC",
NIST Special Publication 800-38D, November 2007. NIST Special Publication 800-38D, November 2007.
[I-D.ietf-tls-negotiated-ff-dhe] [I-D.sandj-tls-iana-registry-updates]
Gillmor, D., "Negotiated Finite Field Diffie-Hellman Salowey, J. and S. Turner, "D/TLS IANA Registry Updates",
Ephemeral Parameters for TLS", draft-ietf-tls-negotiated- draft-sandj-tls-iana-registry-updates-00 (work in
ff-dhe-10 (work in progress), June 2015. progress), September 2016.
[IEEE1363] [IEEE1363]
IEEE, "Standard Specifications for Public Key IEEE, "Standard Specifications for Public Key
Cryptography", IEEE 1363 , 2000. Cryptography", IEEE 1363 , 2000.
[LXZFH16] Li, X., Xu, J., Feng, D., Zhang, Z., and H. Hu, "Multiple [LXZFH16] Li, X., Xu, J., Feng, D., Zhang, Z., and H. Hu, "Multiple
Handshakes Security of TLS 1.3 Candidates", Proceedings of Handshakes Security of TLS 1.3 Candidates", Proceedings of
IEEE Symposium on Security and Privacy (Oakland) 2016 , IEEE Symposium on Security and Privacy (Oakland) 2016 ,
2016. 2016.
skipping to change at page 88, line 34 skipping to change at page 91, line 15
[RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
Langley, A., and M. Ray, "Transport Layer Security (TLS) Langley, A., and M. Ray, "Transport Layer Security (TLS)
Session Hash and Extended Master Secret Extension", Session Hash and Extended Master Secret Extension",
RFC 7627, DOI 10.17487/RFC7627, September 2015, RFC 7627, DOI 10.17487/RFC7627, September 2015,
<http://www.rfc-editor.org/info/rfc7627>. <http://www.rfc-editor.org/info/rfc7627>.
[RFC7685] Langley, A., "A Transport Layer Security (TLS) ClientHello [RFC7685] Langley, A., "A Transport Layer Security (TLS) ClientHello
Padding Extension", RFC 7685, DOI 10.17487/RFC7685, Padding Extension", RFC 7685, DOI 10.17487/RFC7685,
October 2015, <http://www.rfc-editor.org/info/rfc7685>. October 2015, <http://www.rfc-editor.org/info/rfc7685>.
[RFC7919] Gillmor, D., "Negotiated Finite Field Diffie-Hellman
Ephemeral Parameters for Transport Layer Security (TLS)",
RFC 7919, DOI 10.17487/RFC7919, August 2016,
<http://www.rfc-editor.org/info/rfc7919>.
[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security [RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924, (TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016, DOI 10.17487/RFC7924, July 2016,
<http://www.rfc-editor.org/info/rfc7924>. <http://www.rfc-editor.org/info/rfc7924>.
[RSA] Rivest, R., Shamir, A., and L. Adleman, "A Method for [RSA] Rivest, R., Shamir, A., and L. Adleman, "A Method for
Obtaining Digital Signatures and Public-Key Obtaining Digital Signatures and Public-Key
Cryptosystems", Communications of the ACM v. 21, n. 2, pp. Cryptosystems", Communications of the ACM v. 21, n. 2, pp.
120-126., February 1978. 120-126., February 1978.
skipping to change at page 90, line 19 skipping to change at page 93, line 19
here for completeness. TLS 1.3 implementations MUST NOT send them here for completeness. TLS 1.3 implementations MUST NOT send them
but might receive them from older TLS implementations. but might receive them from older TLS implementations.
A.1. Record Layer A.1. Record Layer
enum { enum {
invalid_RESERVED(0), invalid_RESERVED(0),
change_cipher_spec_RESERVED(20), change_cipher_spec_RESERVED(20),
alert(21), alert(21),
handshake(22), handshake(22),
application_data(23) application_data(23),
(255) (255)
} ContentType; } ContentType;
struct { struct {
ContentType type; ContentType type;
ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */ ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */
uint16 length; uint16 length;
opaque fragment[TLSPlaintext.length]; opaque fragment[TLSPlaintext.length];
} TLSPlaintext; } TLSPlaintext;
struct { struct {
opaque content[TLSPlaintext.length]; opaque content[TLSPlaintext.length];
ContentType type; ContentType type;
uint8 zeros[length_of_padding]; uint8 zeros[length_of_padding];
} TLSInnerPlaintext; } TLSInnerPlaintext;
struct { struct {
ContentType opaque_type = application_data(23); /* see fragment.type */ ContentType opaque_type = application_data(23); /* see TLSInnerPlaintext.type */
ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */ ProtocolVersion legacy_record_version = { 3, 1 }; /* TLS v1.x */
uint16 length; uint16 length;
opaque encrypted_record[length]; opaque encrypted_record[length];
} TLSCiphertext; } TLSCiphertext;
A.2. Alert Messages A.2. Alert Messages
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
skipping to change at page 91, line 40 skipping to change at page 94, line 40
inappropriate_fallback(86), inappropriate_fallback(86),
user_canceled(90), user_canceled(90),
no_renegotiation_RESERVED(100), no_renegotiation_RESERVED(100),
missing_extension(109), missing_extension(109),
unsupported_extension(110), unsupported_extension(110),
certificate_unobtainable(111), certificate_unobtainable(111),
unrecognized_name(112), unrecognized_name(112),
bad_certificate_status_response(113), bad_certificate_status_response(113),
bad_certificate_hash_value(114), bad_certificate_hash_value(114),
unknown_psk_identity(115), unknown_psk_identity(115),
certificate_required(116),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
A.3. Handshake Protocol A.3. Handshake Protocol
skipping to change at page 92, line 28 skipping to change at page 95, line 28
certificate_verify(15), certificate_verify(15),
client_key_exchange_RESERVED(16), client_key_exchange_RESERVED(16),
finished(20), finished(20),
key_update(24), key_update(24),
(255) (255)
} HandshakeType; } HandshakeType;
struct { struct {
HandshakeType msg_type; /* handshake type */ HandshakeType msg_type; /* handshake type */
uint24 length; /* bytes in message */ uint24 length; /* bytes in message */
select (HandshakeType) { select (Handshake.msg_type) {
case client_hello: ClientHello; case client_hello: ClientHello;
case server_hello: ServerHello; case server_hello: ServerHello;
case hello_retry_request: HelloRetryRequest; case hello_retry_request: HelloRetryRequest;
case encrypted_extensions: EncryptedExtensions; case encrypted_extensions: EncryptedExtensions;
case certificate_request: CertificateRequest; case certificate_request: CertificateRequest;
case certificate: Certificate; case certificate: Certificate;
case certificate_verify: CertificateVerify; case certificate_verify: CertificateVerify;
case finished: Finished; case finished: Finished;
case new_session_ticket: NewSessionTicket; case new_session_ticket: NewSessionTicket;
case key_update: KeyUpdate; case key_update: KeyUpdate;
} body; } body;
} Handshake; } Handshake;
A.3.1. Key Exchange Messages A.3.1. Key Exchange Messages
struct { struct {
uint8 major; uint8 major;
uint8 minor; uint8 minor;
} ProtocolVersion; } ProtocolVersion;
struct { struct {
opaque random_bytes[32]; opaque random_bytes[32];
} Random; } Random;
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
struct { struct {
ProtocolVersion max_supported_version = { 3, 4 }; /* TLS v1.3 */ ProtocolVersion legacy_version = { 3, 3 }; /* TLS v1.2 */
Random random; Random random;
opaque legacy_session_id<0..32>; opaque legacy_session_id<0..32>;
CipherSuite cipher_suites<2..2^16-2>; CipherSuite cipher_suites<2..2^16-2>;
opaque legacy_compression_methods<1..2^8-1>; opaque legacy_compression_methods<1..2^8-1>;
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} ClientHello; } ClientHello;
struct { struct {
ProtocolVersion version; ProtocolVersion version;
Random random; Random random;
CipherSuite cipher_suite; CipherSuite cipher_suite;
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} ServerHello; } ServerHello;
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
NamedGroup selected_group; Extension extensions<2..2^16-1>;
Extension extensions<0..2^16-1>; } HelloRetryRequest;
} HelloRetryRequest;
struct { struct {
ExtensionType extension_type; ExtensionType extension_type;
opaque extension_data<0..2^16-1>; opaque extension_data<0..2^16-1>;
} Extension; } Extension;
enum { enum {
supported_groups(10), supported_groups(10),
signature_algorithms(13), signature_algorithms(13),
key_share(40), key_share(40),
pre_shared_key(41), pre_shared_key(41),
early_data(42), early_data(42),
cookie(44), supported_versions(43),
(65535) cookie(44),
} ExtensionType; (65535)
} ExtensionType;
struct { struct {
NamedGroup group; NamedGroup group;
opaque key_exchange<1..2^16-1>; opaque key_exchange<1..2^16-1>;
} KeyShareEntry; } KeyShareEntry;
struct { struct {
select (role) { select (Handshake.msg_type) {
case client: case client_hello:
KeyShareEntry client_shares<0..2^16-1>; KeyShareEntry client_shares<0..2^16-1>;
case server: case hello_retry_request:
KeyShareEntry server_share; NamedGroup selected_group;
}
} KeyShare;
enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeModes; case server_hello:
enum { psk_auth(0), psk_sign_auth(1), (255) } PskAuthenticationModes; KeyShareEntry server_share;
};
} KeyShare;
opaque psk_identity<0..2^16-1>; enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeMode;
enum { psk_auth(0), psk_sign_auth(1), (255) } PskAuthenticationMode;
struct { struct {
PskKeMode ke_modes<1..255>; PskKeyExchangeMode ke_modes<1..255>;
PskAuthMode auth_modes<1..255>; PskAuthenticationMode auth_modes<1..255>;
opaque identity<0..2^16-1>; opaque identity<0..2^16-1>;
} PskIdentity; } PskIdentity;
struct { struct {
select (Role) { select (Handshake.msg_type) {
case client: case client_hello:
psk_identity identities<2..2^16-1>; PskIdentity identities<6..2^16-1>;
case server: case server_hello:
uint16 selected_identity; uint16 selected_identity;
} };
} PreSharedKeyExtension; } PreSharedKeyExtension;
struct { struct {
select (Role) { select (Handshake.msg_type) {
case client: case client_hello:
uint32 obfuscated_ticket_age; uint32 obfuscated_ticket_age;
case server: case server_hello:
struct {}; struct {};
} };
} EarlyDataIndication; } EarlyDataIndication;
A.3.1.1. Cookie Extension A.3.1.1. Version Extension
struct {
ProtocolVersion versions<2..254>;
} SupportedVersions;
A.3.1.2. Cookie Extension
struct { struct {
opaque cookie<0..2^16-1>; opaque cookie<0..2^16-1>;
} Cookie; } Cookie;
A.3.1.2. Signature Algorithm Extension A.3.1.3. Signature Algorithm Extension
enum { enum {
/* RSASSA-PKCS1-v1_5 algorithms */ /* RSASSA-PKCS1-v1_5 algorithms */
rsa_pkcs1_sha1 (0x0201), rsa_pkcs1_sha1 (0x0201),
rsa_pkcs1_sha256 (0x0401), rsa_pkcs1_sha256 (0x0401),
rsa_pkcs1_sha384 (0x0501), rsa_pkcs1_sha384 (0x0501),
rsa_pkcs1_sha512 (0x0601), rsa_pkcs1_sha512 (0x0601),
/* ECDSA algorithms */ /* ECDSA algorithms */
ecdsa_secp256r1_sha256 (0x0403), ecdsa_secp256r1_sha256 (0x0403),
ecdsa_secp384r1_sha384 (0x0503), ecdsa_secp384r1_sha384 (0x0503),
ecdsa_secp521r1_sha512 (0x0603), ecdsa_secp521r1_sha512 (0x0603),
/* RSASSA-PSS algorithms */ /* RSASSA-PSS algorithms */
rsa_pss_sha256 (0x0700), rsa_pss_sha256 (0x0804),
rsa_pss_sha384 (0x0701), rsa_pss_sha384 (0x0805),
rsa_pss_sha512 (0x0702), rsa_pss_sha512 (0x0806),
/* EdDSA algorithms */ /* EdDSA algorithms */
ed25519 (0x0703), ed25519 (0x0807),
ed448 (0x0704), ed448 (0x0808),
/* Reserved Code Points */ /* Reserved Code Points */
dsa_sha1_RESERVED (0x0202), dsa_sha1_RESERVED (0x0202),
dsa_sha256_RESERVED (0x0402), dsa_sha256_RESERVED (0x0402),
dsa_sha384_RESERVED (0x0502), dsa_sha384_RESERVED (0x0502),
dsa_sha512_RESERVED (0x0602), dsa_sha512_RESERVED (0x0602),
ecdsa_sha1_RESERVED (0x0203), ecdsa_sha1_RESERVED (0x0203),
obsolete_RESERVED (0x0000..0x0200), obsolete_RESERVED (0x0000..0x0200),
obsolete_RESERVED (0x0204..0x0400), obsolete_RESERVED (0x0204..0x0400),
obsolete_RESERVED (0x0404..0x0500), obsolete_RESERVED (0x0404..0x0500),
obsolete_RESERVED (0x0504..0x0600), obsolete_RESERVED (0x0504..0x0600),
obsolete_RESERVED (0x0604..0x06FF), obsolete_RESERVED (0x0604..0x06FF),
private_use (0xFE00..0xFFFF), private_use (0xFE00..0xFFFF),
(0xFFFF) (0xFFFF)
} SignatureScheme; } SignatureScheme;
SignatureScheme supported_signature_algorithms<2..2^16-2>; SignatureScheme supported_signature_algorithms<2..2^16-2>;
A.3.1.3. Supported Groups Extension A.3.1.4. Supported Groups Extension
enum { enum {
/* Elliptic Curve Groups (ECDHE) */ /* Elliptic Curve Groups (ECDHE) */
obsolete_RESERVED (1..22), obsolete_RESERVED (1..22),
secp256r1 (23), secp384r1 (24), secp521r1 (25), secp256r1 (23), secp384r1 (24), secp521r1 (25),
obsolete_RESERVED (26..28), obsolete_RESERVED (26..28),
x25519 (29), x448 (30), x25519 (29), x448 (30),
/* Finite Field Groups (DHE) */ /* Finite Field Groups (DHE) */
ffdhe2048 (256), ffdhe3072 (257), ffdhe4096 (258), ffdhe2048 (256), ffdhe3072 (257), ffdhe4096 (258),
ffdhe6144 (259), ffdhe8192 (260), ffdhe6144 (259), ffdhe8192 (260),
/* Reserved Code Points */ /* Reserved Code Points */
ffdhe_private_use (0x01FC..0x01FF), ffdhe_private_use (0x01FC..0x01FF),
ecdhe_private_use (0xFE00..0xFEFF), ecdhe_private_use (0xFE00..0xFEFF),
obsolete_RESERVED (0xFF01..0xFF02), obsolete_RESERVED (0xFF01..0xFF02),
(0xFFFF) (0xFFFF)
} NamedGroup; } NamedGroup;
struct { struct {
NamedGroup named_group_list<1..2^16-1>; NamedGroup named_group_list<2..2^16-1>;
} NamedGroupList; } NamedGroupList;
Values within "obsolete_RESERVED" ranges were used in previous Values within "obsolete_RESERVED" ranges were used in previous
versions of TLS and MUST NOT be offered or negotiated by TLS 1.3 versions of TLS and MUST NOT be offered or negotiated by TLS 1.3
implementations. The obsolete curves have various known/theoretical implementations. The obsolete curves have various known/theoretical
weaknesses or have had very little usage, in some cases only due to weaknesses or have had very little usage, in some cases only due to
unintentional server configuration issues. They are no longer unintentional server configuration issues. They are no longer
considered appropriate for general use and should be assumed to be considered appropriate for general use and should be assumed to be
potentially unsafe. The set of curves specified here is sufficient potentially unsafe. The set of curves specified here is sufficient
for interoperability with all currently deployed and properly for interoperability with all currently deployed and properly
configured TLS implementations. configured TLS implementations.
A.3.1.4. Deprecated Extensions A.3.1.5. Deprecated Extensions
The following extensions are no longer applicable to TLS 1.3, The following extensions are no longer applicable to TLS 1.3,
although TLS 1.3 clients MAY send them if they are willing to although TLS 1.3 clients MAY send them if they are willing to
negotiate them with prior versions of TLS. TLS 1.3 servers MUST negotiate them with prior versions of TLS. TLS 1.3 servers MUST
ignore these extensions if they are negotiating TLS 1.3: ignore these extensions if they are negotiating TLS 1.3:
truncated_hmac [RFC6066], srp [RFC5054], encrypt_then_mac [RFC7366], truncated_hmac [RFC6066], srp [RFC5054], encrypt_then_mac [RFC7366],
extended_master_secret [RFC7627], SessionTicket [RFC5077], and extended_master_secret [RFC7627], SessionTicket [RFC5077], and
renegotiation_info [RFC5746]. renegotiation_info [RFC5746].
A.3.2. Server Parameters Messages A.3.2. Server Parameters Messages
skipping to change at page 98, line 4 skipping to change at page 101, line 4
struct { struct {
SignatureScheme algorithm; SignatureScheme algorithm;
opaque signature<0..2^16-1>; opaque signature<0..2^16-1>;
} CertificateVerify; } CertificateVerify;
struct { struct {
opaque verify_data[Hash.length]; opaque verify_data[Hash.length];
} Finished; } Finished;
A.3.4. Ticket Establishment A.3.4. Ticket Establishment
enum { (65535) } TicketExtensionType; enum { ticket_early_data_info(1), (65535) } TicketExtensionType;
struct { struct {
TicketExtensionType extension_type; TicketExtensionType extension_type;
opaque extension_data<1..2^16-1>; opaque extension_data<1..2^16-1>;
} TicketExtension; } TicketExtension;
struct {
uint32 ticket_lifetime;
PskKeyExchangeMode ke_modes<1..255>;
PskAuthenticationMode auth_modes<1..255>;
opaque ticket<1..2^16-1>;
TicketExtension extensions<0..2^16-2>;
} NewSessionTicket;
A.3.5. Updating Keys
enum { update_not_requested(0), update_requested(1), (255)
} KeyUpdateRequest;
struct { struct {
uint32 ticket_lifetime; KeyUpdateRequest request_update;
PskKeMode ke_modes<1..255>; } KeyUpdate;
PskAuthMode auth_modes<1..255>;
opaque ticket<1..2^16-1>;
TicketExtension extensions<0..2^16-2>;
} NewSessionTicket;
A.4. Cipher Suites A.4. Cipher Suites
A symmetric cipher suite defines the pair of the AEAD cipher and hash A symmetric cipher suite defines the pair of the AEAD algorithm and
function to be used with HKDF. Cipher suites follow the naming hash algorithm to be used with HKDF. Cipher suite names follow the
convention: Cipher suite names follow the naming convention: naming convention:
CipherSuite TLS13_CIPHER_HASH = VALUE; CipherSuite TLS_AEAD_HASH = VALUE;
+-----------+-------------------------------------------------+ +-----------+------------------------------------------------+
| Component | Contents | | Component | Contents |
+-----------+-------------------------------------------------+ +-----------+------------------------------------------------+
| TLS | The string "TLS" | | TLS | The string "TLS" |
| | | | | |
| CIPHER | The symmetric cipher used for record protection | | AEAD | The AEAD algorithm used for record protection |
| | | | | |
| HASH | The hash algorithm used with HKDF | | HASH | The hash algorithm used with HKDF |
| | | | | |
| VALUE | The two byte ID assigned for this cipher suite | | VALUE | The two byte ID assigned for this cipher suite |
+-----------+-------------------------------------------------+ +-----------+------------------------------------------------+
The "CIPHER" component commonly has sub-components used to designate This specification defines the following cipher suites for use with
the cipher name, bits, and mode, if applicable. For example, TLS 1.3.
"AES_256_GCM" represents 256-bit AES in the GCM mode of operation.
+------------------------------+-------------+---------------+ +------------------------------+-------------+
| Cipher Suite Name | Value | Specification | | Description | Value |
+------------------------------+-------------+---------------+ +------------------------------+-------------+
| TLS_AES_128_GCM_SHA256 | {0x13,0x01} | [This RFC] | | TLS_AES_128_GCM_SHA256 | {0x13,0x01} |
| | | | | | |
| TLS_AES_256_GCM_SHA384 | {0x13,0x02} | [This RFC] | | TLS_AES_256_GCM_SHA384 | {0x13,0x02} |
| | | | | | |
| TLS_CHACHA20_POLY1305_SHA256 | {0x13,0x03} | [This RFC] | | TLS_CHACHA20_POLY1305_SHA256 | {0x13,0x03} |
| | | | | | |
| TLS_AES_128_CCM_SHA256 | {0x13,0x04} | [This RFC] | | TLS_AES_128_CCM_SHA256 | {0x13,0x04} |
| | | | | | |
| TLS_AES_128_CCM_8_SHA256 | {0x13,0x05} | [This RFC] | | TLS_AES_128_CCM_8_SHA256 | {0x13,0x05} |
+------------------------------+-------------+---------------+ +------------------------------+-------------+
The corresponding AEAD algorithms AEAD_AES_128_GCM, AEAD_AES_256_GCM,
and AEAD_AES_128_CCM are defined in [RFC5116].
AEAD_CHACHA20_POLY1305 is defined in [RFC7539]. AEAD_AES_128_CCM_8
is defined in [RFC6655]. The corresponding hash algorithms are
defined in [SHS].
Although TLS 1.3 uses the same cipher suite space as previous Although TLS 1.3 uses the same cipher suite space as previous
versions of TLS, TLS 1.3 cipher suites are defined differently, only versions of TLS, TLS 1.3 cipher suites are defined differently, only
specifying the symmetric ciphers, and cannot it be used for TLS 1.2. specifying the symmetric ciphers, and cannot it be used for TLS 1.2.
Similarly, TLS 1.2 and lower cipher suites cannot be used with TLS Similarly, TLS 1.2 and lower cipher suites cannot be used with TLS
1.3. 1.3.
New cipher suite values are assigned by IANA as described in New cipher suite values are assigned by IANA as described in
Section 10. Section 10.
A.4.1. Unauthenticated Operation
Previous versions of TLS offered explicitly unauthenticated cipher
suites based on anonymous Diffie-Hellman. These cipher suites have
been deprecated in TLS 1.3. However, it is still possible to
negotiate cipher suites that do not provide verifiable server
authentication by several methods, including:
- Raw public keys [RFC7250].
- Using a public key contained in a certificate but without
validation of the certificate chain or any of its contents.
Either technique used alone is are vulnerable to man-in-the-middle
attacks and therefore unsafe for general use. However, it is also
possible to bind such connections to an external authentication
mechanism via out-of-band validation of the server's public key,
trust on first use, or channel bindings [RFC5929]. [[NOTE: TLS 1.3
needs a new channel binding definition that has not yet been
defined.]] If no such mechanism is used, then the connection has no
protection against active man-in-the-middle attack; applications MUST
NOT use TLS in such a way absent explicit configuration or a specific
application profile.
Appendix B. Implementation Notes Appendix B. 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.
B.1. API considerations for 0-RTT B.1. API considerations for 0-RTT
0-RTT data has very different security properties from data 0-RTT data has very different security properties from data
transmitted after a completed handshake: it can be replayed. transmitted after a completed handshake: it can be replayed.
Implementations SHOULD provide different functions for reading and Implementations SHOULD provide different functions for reading and
writing 0-RTT data and data transmitted after the handshake, and writing 0-RTT data and data transmitted after the handshake, and
SHOULD NOT automatically resend 0-RTT data if it is rejected by the SHOULD NOT automatically resend 0-RTT data if it is rejected by the
server. server.
B.2. Random Number Generation and Seeding B.2. Random Number Generation and Seeding
TLS requires a cryptographically secure pseudorandom number generator TLS requires a cryptographically secure pseudorandom number generator
(PRNG). In most cases, the operating system provides an appropriate (PRNG). In most cases, the operating system provides an appropriate
facility such as /dev/urandom, which should be used absent other facility such as /dev/urandom, which should be used absent other
(performance) concerns. It is generally preferrable to use an (performance) concerns. It is generally preferable to use an
existing PRNG implementation in preference to crafting a new one, and existing PRNG implementation in preference to crafting a new one, and
many adequate cryptographic libraries are already available under many adequate cryptographic libraries are already available under
favorable license terms. Should those prove unsatisfactory, favorable license terms. Should those prove unsatisfactory,
[RFC4086] provides guidance on the generation of random values. [RFC4086] provides guidance on the generation of random values.
B.3. Certificates and Authentication B.3. 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
skipping to change at page 101, line 33 skipping to change at page 104, line 9
- Do you ignore the TLS record layer version number in all TLS - Do you ignore the TLS record layer version number in all TLS
records? (see Appendix C) records? (see Appendix C)
- Have you ensured that all support for SSL, RC4, EXPORT ciphers, - Have you ensured that all support for SSL, RC4, EXPORT ciphers,
and MD5 (via the "signature_algorithm" extension) is completely and MD5 (via the "signature_algorithm" extension) is completely
removed from all possible configurations that support TLS 1.3 or removed from all possible configurations that support TLS 1.3 or
later, and that attempts to use these obsolete capabilities fail later, and that attempts to use these obsolete capabilities fail
correctly? (see Appendix C) correctly? (see Appendix C)
- Do you handle TLS extensions in ClientHello correctly, including - Do you handle TLS extensions in ClientHello correctly, including
unknown extensions or omitting the extensions field completely? unknown extensions.
- When the server has requested a client certificate, but no - When the server has requested a client certificate, but no
suitable certificate is available, do you correctly send an empty suitable certificate is available, do you correctly send an empty
Certificate message, instead of omitting the whole message (see Certificate message, instead of omitting the whole message (see
Section 4.3.1.2)? Section 4.4.1.2)?
- When processing the plaintext fragment produced by AEAD-Decrypt - When processing the plaintext fragment produced by AEAD-Decrypt
and scanning from the end for the ContentType, do you avoid and scanning from the end for the ContentType, do you avoid
scanning past the start of the cleartext in the event that the scanning past the start of the cleartext in the event that the
peer has sent a malformed plaintext of all-zeros? peer has sent a malformed plaintext of all-zeros?
- When processing a ClientHello containing a version of { 3, 5 } or - When processing a ClientHello containing a version of { 3, 5 } or
higher, do you respond with the highest common version of TLS higher, do you respond with the highest common version of TLS
rather than requiring an exact match? Have you ensured this rather than requiring an exact match? Have you ensured this
continues to be true with arbitrarily higher version numbers? continues to be true with arbitrarily higher version numbers?
(e.g. { 4, 0 }, { 9, 9 }, { 255, 255 }) (e.g. { 4, 0 }, { 9, 9 }, { 255, 255 })
- Do you properly ignore unrecognized cipher suites (Section 4.1.2), - Do you properly ignore unrecognized cipher suites (Section 4.1.2),
hello extensions (Section 4.2), named groups (Section 4.2.3), and hello extensions (Section 4.2), named groups (Section 4.2.4), and
signature algorithms (Section 4.2.2)? signature algorithms (Section 4.2.3)?
Cryptographic details: Cryptographic details:
- What countermeasures do you use to prevent timing attacks against - What countermeasures do you use to prevent timing attacks
RSA signing operations [TIMING]? [TIMING]?
- When verifying RSA signatures, do you accept both NULL and missing - When verifying RSA signatures, do you accept both NULL and missing
parameters? Do you verify that the RSA padding doesn't have parameters? Do you verify that the RSA padding doesn't have
additional data after the hash value? [FI06] additional data after the hash value? [FI06]
- When using Diffie-Hellman key exchange, do you correctly preserve - When using Diffie-Hellman key exchange, do you correctly preserve
leading zero bytes in the negotiated key (see Section 7.3.1)? leading zero bytes in the negotiated key (see Section 7.3.1)?
- Does your TLS client check that the Diffie-Hellman parameters sent - Does your TLS client check that the Diffie-Hellman parameters sent
by the server are acceptable, (see Section 4.2.4.1)? by the server are acceptable, (see Section 4.2.5.1)?
- Do you use a strong and, most importantly, properly seeded random - Do you use a strong and, most importantly, properly seeded random
number generator (see Appendix B.2) when generating Diffie-Hellman number generator (see Appendix B.2) when generating Diffie-Hellman
private values, the ECDSA "k" parameter, and other security- private values, the ECDSA "k" parameter, and other security-
critical values? It is RECOMMENDED that implementations implement critical values? It is RECOMMENDED that implementations implement
"deterministic ECDSA" as specified in [RFC6979]. "deterministic ECDSA" as specified in [RFC6979].
- Do you zero-pad Diffie-Hellman public key values to the group size - Do you zero-pad Diffie-Hellman public key values to the group size
(see Section 4.2.4.1)? (see Section 4.2.5.1)?
B.6. Client Tracking Prevention B.6. Client Tracking Prevention
Clients SHOULD NOT reuse a session ticket for multiple connections. Clients SHOULD NOT reuse a session ticket for multiple connections.
Reuse of a session ticket allows passive observers to correlate Reuse of a session ticket allows passive observers to correlate
different connections. Servers that issue session tickets SHOULD different connections. Servers that issue session tickets SHOULD
offer at least as many session tickets as the number of connections offer at least as many session tickets as the number of connections
that a client might use; for example, a web browser using HTTP/1.1 that a client might use; for example, a web browser using HTTP/1.1
[RFC7230] might open six connections to a server. Servers SHOULD [RFC7230] might open six connections to a server. Servers SHOULD
issue new session tickets with every connection. This ensures that issue new session tickets with every connection. This ensures that
clients are always able to use a new session ticket when creating a clients are always able to use a new session ticket when creating a
new connection. new connection.
B.7. Unauthenticated Operation
Previous versions of TLS offered explicitly unauthenticated cipher
suites based on anonymous Diffie-Hellman. These modes have been
deprecated in TLS 1.3. However, it is still possible to negotiate
parameters that do not provide verifiable server authentication by
several methods, including:
- Raw public keys [RFC7250].
- Using a public key contained in a certificate but without
validation of the certificate chain or any of its contents.
Either technique used alone is vulnerable to man-in-the-middle
attacks and therefore unsafe for general use. However, it is also
possible to bind such connections to an external authentication
mechanism via out-of-band validation of the server's public key,
trust on first use, or channel bindings [RFC5929]. [[NOTE: TLS 1.3
needs a new channel binding definition that has not yet been
defined.]] If no such mechanism is used, then the connection has no
protection against active man-in-the-middle attack; applications MUST
NOT use TLS in such a way absent explicit configuration or a specific
application profile.
Appendix C. Backward Compatibility Appendix C. Backward Compatibility
The TLS protocol provides a built-in mechanism for version The TLS protocol provides a built-in mechanism for version
negotiation between endpoints potentially supporting different negotiation between endpoints potentially supporting different
versions of TLS. versions of TLS.
TLS 1.x and SSL 3.0 use compatible ClientHello messages. Servers can TLS 1.x and SSL 3.0 use compatible ClientHello messages. Servers can
also handle clients trying to use future versions of TLS as long as also handle clients trying to use future versions of TLS as long as
the ClientHello format remains compatible and the client supports the the ClientHello format remains compatible and the client supports the
highest protocol version available in the server. highest protocol version available in the server.
Prior versions of TLS used the record layer version number for Prior versions of TLS used the record layer version number for
various purposes. (TLSPlaintext.legacy_record_version & various purposes. (TLSPlaintext.legacy_record_version &
TLSCiphertext.legacy_record_version) As of TLS 1.3, this field is TLSCiphertext.legacy_record_version) As of TLS 1.3, this field is
deprecated and its value MUST be ignored by all implementations. deprecated and its value MUST be ignored by all implementations.
Version negotiation is performed using only the handshake versions. Version negotiation is performed using only the handshake versions.
(ClientHello.max_supported_version & ServerHello.version) In order to (ClientHello.legacy_version, ClientHello "supported_versions"
maximize interoperability with older endpoints, implementations that extension & ServerHello.version) In order to maximize
negotiate the use of TLS 1.0-1.2 SHOULD set the record layer version interoperability with older endpoints, implementations that negotiate
number to the negotiated version for the ServerHello and all records the use of TLS 1.0-1.2 SHOULD set the record layer version number to
the negotiated version for the ServerHello and all records
thereafter. thereafter.
For maximum compatibility with previously non-standard behavior and For maximum compatibility with previously non-standard behavior and
misconfigured deployments, all implementations SHOULD support misconfigured deployments, all implementations SHOULD support
validation of certification paths based on the expectations in this validation of certification paths based on the expectations in this
document, even when handling prior TLS versions' handshakes. (see document, even when handling prior TLS versions' handshakes. (see
Section 4.3.1.1) Section 4.4.1.1)
TLS 1.2 and prior supported an "Extended Master Secret" [RFC7627] TLS 1.2 and prior supported an "Extended Master Secret" [RFC7627]
extension which digested large parts of the handshake transcript into extension which digested large parts of the handshake transcript into
the master secret. Because TLS 1.3 always hashes in the transcript the master secret. Because TLS 1.3 always hashes in the transcript
up to the server CertificateVerify, implementations which support up to the server CertificateVerify, implementations which support
both TLS 1.3 and earlier versions SHOULD indicate the use of the both TLS 1.3 and earlier versions SHOULD indicate the use of the
Extended Master Secret extension in their APIs whenever TLS 1.3 is Extended Master Secret extension in their APIs whenever TLS 1.3 is
used. used.
C.1. Negotiating with an older server C.1. Negotiating with an older server
A TLS 1.3 client who wishes to negotiate with such older servers will A TLS 1.3 client who wishes to negotiate with such older servers will
send a normal TLS 1.3 ClientHello containing { 3, 4 } (TLS 1.3) in send a normal TLS 1.3 ClientHello containing { 3, 3 } (TLS 1.2) in
ClientHello.max_supported_version. If the server does not support ClientHello.legacy_version but with the correct version in the
this version it will respond with a ServerHello containing an older "supported_versions" extension. If the server does not support TLS
version number. If the client agrees to use this version, the 1.3 it will respond with a ServerHello containing an older version
negotiation will proceed as appropriate for the negotiated protocol. number. If the client agrees to use this version, the negotiation
A client resuming a session SHOULD initiate the connection using the will proceed as appropriate for the negotiated protocol. A client
version that was previously negotiated. resuming a session SHOULD initiate the connection using the version
that was previously negotiated.
Note that 0-RTT data is not compatible with older servers. See Note that 0-RTT data is not compatible with older servers. See
Appendix C.3. Appendix C.3.
If the version chosen by the server is not supported by the client If the version chosen by the server is not supported by the client
(or not acceptable), the client MUST send a "protocol_version" alert (or not acceptable), the client MUST abort the handshake with a
message and close the connection. "protocol_version" alert.
If a TLS server receives a ClientHello containing a version number If a TLS server receives a ClientHello containing a version number
greater than the highest version supported by the server, it MUST greater than the highest version supported by the server, it MUST
reply according to the highest version supported by the server. reply according to the highest version supported by the server.
Some legacy server implementations are known to not implement the TLS Some legacy server implementations are known to not implement the TLS
specification properly and might abort connections upon encountering specification properly and might abort connections upon encountering
TLS extensions or versions which it is not aware of. TLS extensions or versions which it is not aware of.
Interoperability with buggy servers is a complex topic beyond the Interoperability with buggy servers is a complex topic beyond the
scope of this document. Multiple connection attempts may be required scope of this document. Multiple connection attempts may be required
in order to negotiate a backwards compatible connection, however this in order to negotiate a backwards compatible connection, however this
practice is vulnerable to downgrade attacks and is NOT RECOMMENDED. practice is vulnerable to downgrade attacks and is NOT RECOMMENDED.
C.2. Negotiating with an older client C.2. Negotiating with an older client
A TLS server can also receive a ClientHello containing a version A TLS server can also receive a ClientHello indicating a version
number smaller than the highest supported version. If the server number smaller than its highest supported version. If the
wishes to negotiate with old clients, it will proceed as appropriate "supported_versions" extension is present, the server MUST negotiate
for the highest version supported by the server that is not greater the highest server-supported version found in that extension. If the
than ClientHello.max_supported_version. For example, if the server "supported_versions" extension is not present, the server MUST
supports TLS 1.0, 1.1, and 1.2, and max_supported_version is TLS 1.0, negotiate the minimum of ClientHello.legacy_version and TLS 1.2.For
the server will proceed with a TLS 1.0 ServerHello. If the server example, if the server supports TLS 1.0, 1.1, and 1.2, and
only supports versions greater than max_supported_version, it MUST legacy_version is TLS 1.0, the server will proceed with a TLS 1.0
send a "protocol_version" alert message and close the connection. ServerHello. If the server only supports versions greater than
ClientHello.legacy_version, it MUST abort the handshake with a
"protocol_version" alert.
Note that earlier versions of TLS did not clearly specify the record Note that earlier versions of TLS did not clearly specify the record
layer version number value in all cases layer version number value in all cases
(TLSPlaintext.legacy_record_version). Servers will receive various (TLSPlaintext.legacy_record_version). Servers will receive various
TLS 1.x versions in this field, however its value MUST always be TLS 1.x versions in this field, however its value MUST always be
ignored. ignored.
C.3. Zero-RTT backwards compatibility C.3. Zero-RTT backwards compatibility
0-RTT data is not compatible with older servers. An older server 0-RTT data is not compatible with older servers. An older server
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RECOMMENDED to accept an SSL version 2.0 compatible CLIENT-HELLO in RECOMMENDED to accept an SSL version 2.0 compatible CLIENT-HELLO in
order to negotiate older versions of TLS. order to negotiate older versions of TLS.
Implementations MUST NOT send or accept any records with a version Implementations MUST NOT send or accept any records with a version
less than { 3, 0 }. less than { 3, 0 }.
The security of SSL 3.0 [SSL3] is considered insufficient for the The security of SSL 3.0 [SSL3] is considered insufficient for the
reasons enumerated in [RFC7568], and MUST NOT be negotiated for any reasons enumerated in [RFC7568], and MUST NOT be negotiated for any
reason. reason.
Implementations MUST NOT send a ClientHello.max_supported_version or Implementations MUST NOT send a ClientHello.legacy_version or
ServerHello.version set to { 3, 0 } or less. Any endpoint receiving ServerHello.version set to { 3, 0 } or less. Any endpoint receiving
a Hello message with ClientHello.max_supported_version or a Hello message with ClientHello.legacy_version or
ServerHello.version set to { 3, 0 } MUST respond with a ServerHello.version set to { 3, 0 } MUST abort the handshake with a
"protocol_version" alert message and close the connection. "protocol_version" alert.
Implementations MUST NOT use the Truncated HMAC extension, defined in Implementations MUST NOT use the Truncated HMAC extension, defined in
Section 7 of [RFC6066], as it is not applicable to AEAD ciphers and Section 7 of [RFC6066], as it is not applicable to AEAD algorithms
has been shown to be insecure in some scenarios. and has been shown to be insecure in some scenarios.
Appendix D. Overview of Security Properties Appendix D. Overview of Security Properties
[[TODO: This section is still a WIP and needs a bunch more work.]] [[TODO: This section is still a WIP and needs a bunch more work.]]
A complete security analysis of TLS is outside the scope of this A complete security analysis of TLS is outside the scope of this
document. In this section, we provide an informal description the document. In this section, we provide an informal description the
desired properties as well as references to more detailed work in the desired properties as well as references to more detailed work in the
research literature which provides more formal definitions. research literature which provides more formal definitions.
skipping to change at page 107, line 45 skipping to change at page 110, line 45
The PSK and resumption-PSK modes bootstrap from a long-term shared The PSK and resumption-PSK modes bootstrap from a long-term shared
secret into a unique per-connection short-term session key. This secret into a unique per-connection short-term session key. This
secret may have been established in a previous handshake. If secret may have been established in a previous handshake. If
PSK-(EC)DHE modes are used, this session key will also be forward PSK-(EC)DHE modes are used, this session key will also be forward
secret. The resumption-PSK mode has been designed so that the secret. The resumption-PSK mode has been designed so that the
resumption master secret computed by connection N and needed to form resumption master secret computed by connection N and needed to form
connection N+1 is separate from the traffic keys used by connection connection N+1 is separate from the traffic keys used by connection
N, thus providing forward secrecy between the connections. N, thus providing forward secrecy between the connections.
If an exporter is used, then it produces values which are unique and
secret (because they are generated from a unique session key).
Exporters computed with different labels and contexts are
computationally independent, so it is not feasible to compute one
from another or the session secret from the exported value. Note:
exporters can produce arbitrary-length values. If exporters are to
be used as channel bindings, the exported value MUST be large enough
to provide collision resistance.
For all handshake modes, the Finished MAC (and where present, the For all handshake modes, the Finished MAC (and where present, the
signature), prevents downgrade attacks. In addition, the use of signature), prevents downgrade attacks. In addition, the use of
certain bytes in the random nonces as described in Section 4.1.3 certain bytes in the random nonces as described in Section 4.1.3
allows the detection of downgrade to previous TLS versions. allows the detection of downgrade to previous TLS versions.
As soon as the client and the server have exchanged enough As soon as the client and the server have exchanged enough
information to establish shared keys, the remainder of the handshake information to establish shared keys, the remainder of the handshake
is encrypted, thus providing protection against passive attackers. is encrypted, thus providing protection against passive attackers.
Because the server authenticates before the client, the client can Because the server authenticates before the client, the client can
ensure that it only reveals its identity to an authenticated server. ensure that it only reveals its identity to an authenticated server.
Note that implementations must use the provided record padding Note that implementations must use the provided record padding
mechanism during the handshake to avoid leaking information about the mechanism during the handshake to avoid leaking information about the
identities due to length. identities due to length.
The 0-RTT mode of operation generally provides the same security The 0-RTT mode of operation generally provides the same security
properties as 1-RTT data, with the two exceptions that the 0-RTT properties as 1-RTT data, with the two exceptions that the 0-RTT
encryption keys do not provide full forward secrecy and that the the encryption keys do not provide full forward secrecy and that the the
server is not able to guarantee full uniqueness of the handshake server is not able to guarantee full uniqueness of the handshake
(non-replayability) without keeping potentially undue amounts of (non-replayability) without keeping potentially undue amounts of
state. See Section 4.2.6 for one mechanism to limit the exposure to state. See Section 4.2.7 for one mechanism to limit the exposure to
replay. replay.
The reader should refer to the following references for analysis of The reader should refer to the following references for analysis of
the TLS handshake [CHSV16] [FGSW16] [LXZFH16]. the TLS handshake [CHSV16] [FGSW16] [LXZFH16].
D.2. Record Layer D.2. Record Layer
The record layer depends on the handshake producing a strong session The record layer depends on the handshake producing a strong session
key which can be used to derive bidirectional traffic keys and key which can be used to derive bidirectional traffic keys and
nonces. Assuming that is true, and the keys are used for no more nonces. Assuming that is true, and the keys are used for no more
skipping to change at page 108, line 48 skipping to change at page 112, line 10
cause the receiver to accept a record which it has already cause the receiver to accept a record which it has already
accepted or cause the receiver to accept record N+1 without having accepted or cause the receiver to accept record N+1 without having
first processed record N. [[TODO: If we merge in DTLS to this first processed record N. [[TODO: If we merge in DTLS to this
document, we will need to update this guarantee.]] document, we will need to update this guarantee.]]
Length concealment. Given a record with a given external length, the Length concealment. Given a record with a given external length, the
attacker should not be able to determine the amount of the record attacker should not be able to determine the amount of the record
that is content versus padding. that is content versus padding.
Forward security after key change. If the traffic key update Forward security after key change. If the traffic key update
mechanism described in Section 4.4.3 has been used and the mechanism described in Section 4.5.3 has been used and the
previous generation key is deleted, an attacker who compromises previous generation key is deleted, an attacker who compromises
the endpoint should not be able to decrypt traffic encrypted with the endpoint should not be able to decrypt traffic encrypted with
the old key. the old key.
Informally, TLS 1.3 provides these properties by AEAD-protecting the Informally, TLS 1.3 provides these properties by AEAD-protecting the
plaintext with a strong key. AEAD encryption [RFC5116] provides plaintext with a strong key. AEAD encryption [RFC5116] provides
confidentiality and integrity for the data. Non-replayability is confidentiality and integrity for the data. Non-replayability is
provided by using a separate nonce for each record, with the nonce provided by using a separate nonce for each record, with the nonce
being derived from the record sequence number (Section 5.3), with the being derived from the record sequence number (Section 5.3), with the
sequence number being maintained independently at both sides thus sequence number being maintained independently at both sides thus
skipping to change at page 111, line 38 skipping to change at page 114, line 48
david.hopwood@blueyonder.co.uk david.hopwood@blueyonder.co.uk
- Subodh Iyengar - Subodh Iyengar
Facebook Facebook
subodh@fb.com subodh@fb.com
- Daniel Kahn Gillmor - Daniel Kahn Gillmor
ACLU ACLU
dkg@fifthhorseman.net dkg@fifthhorseman.net
- Hubert Kario
Red Hat Inc.
hkario@redhat.com
- Phil Karlton (co-author of SSL 3.0) - Phil Karlton (co-author of SSL 3.0)
- Paul Kocher (co-author of SSL 3.0) - Paul Kocher (co-author of SSL 3.0)
Cryptography Research Cryptography Research
paul@cryptography.com paul@cryptography.com
- Hugo Krawczyk - Hugo Krawczyk
IBM IBM
hugo@ee.technion.ac.il hugo@ee.technion.ac.il
- Adam Langley (co-author of [RFC7627]) - Adam Langley (co-author of [RFC7627])
Google Google
agl@google.com agl@google.com
- Xiaoyin Liu
University of North Carolina at Chapel Hill
xiaoyin.l@outlook.com
- Ilari Liusvaara - Ilari Liusvaara
Independent Independent
ilariliusvaara@welho.com ilariliusvaara@welho.com
- Jan Mikkelsen - Jan Mikkelsen
Transactionware Transactionware
janm@transactionware.com janm@transactionware.com
- Bodo Moeller (co-author of [RFC4492]) - Bodo Moeller (co-author of [RFC4492])
Google Google
bodo@openssl.org bodo@openssl.org
- Erik Nygren - Erik Nygren
Akamai Technologies Akamai Technologies
erik+ietf@nygren.org erik+ietf@nygren.org
- Magnus Nystrom - Magnus Nystrom
RSA Security Microsoft
magnus@rsasecurity.com mnystrom@microsoft.com
- Alfredo Pironti (co-author of [RFC7627]) - Alfredo Pironti (co-author of [RFC7627])
INRIA INRIA
alfredo.pironti@inria.fr alfredo.pironti@inria.fr
- Andrei Popov - Andrei Popov
Microsoft Microsoft
andrei.popov@microsoft.com andrei.popov@microsoft.com
- Marsh Ray (co-author of [RFC7627]) - Marsh Ray (co-author of [RFC7627])
skipping to change at page 113, line 31 skipping to change at page 116, line 50
- Tom Weinstein - Tom Weinstein
- Hoeteck Wee - Hoeteck Wee
Ecole Normale Superieure, Paris Ecole Normale Superieure, Paris
hoeteck@alum.mit.edu hoeteck@alum.mit.edu
- Tim Wright - Tim Wright
Vodafone Vodafone
timothy.wright@vodafone.com timothy.wright@vodafone.com
- Kazu Yamamoto
Internet Initiative Japan Inc.
kazu@iij.ad.jp
Author's Address Author's Address
Eric Rescorla Eric Rescorla
RTFM, Inc. RTFM, Inc.
EMail: ekr@rtfm.com EMail: ekr@rtfm.com
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