draft-ietf-tls-tls13-18.txt   draft-ietf-tls-tls13-19.txt 
Network Working Group E. Rescorla Network Working Group E. Rescorla
Internet-Draft RTFM, Inc. Internet-Draft RTFM, Inc.
Obsoletes: 5077, 5246, 5746 (if October 26, 2016 Obsoletes: 5077, 5246, 5746 (if March 10, 2017
approved) approved)
Updates: 4492, 5705, 6066, 6961 (if Updates: 4492, 5705, 6066, 6961 (if
approved) approved)
Intended status: Standards Track Intended status: Standards Track
Expires: April 29, 2017 Expires: September 11, 2017
The Transport Layer Security (TLS) Protocol Version 1.3 The Transport Layer Security (TLS) Protocol Version 1.3
draft-ietf-tls-tls13-18 draft-ietf-tls-tls13-19
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 37 skipping to change at page 1, line 37
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This Internet-Draft will expire on April 29, 2017. This Internet-Draft will expire on September 11, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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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
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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 . . . . . . . . . . . . . . . . 12 1.3. Updates Affecting TLS 1.2 . . . . . . . . . . . . . . . . 13
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 13 2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 14
2.1. Incorrect DHE Share . . . . . . . . . . . . . . . . . . . 16 2.1. Incorrect DHE Share . . . . . . . . . . . . . . . . . . . 17
2.2. Resumption and Pre-Shared Key (PSK) . . . . . . . . . . . 17 2.2. Resumption and Pre-Shared Key (PSK) . . . . . . . . . . . 18
2.3. Zero-RTT Data . . . . . . . . . . . . . . . . . . . . . . 19 2.3. Zero-RTT Data . . . . . . . . . . . . . . . . . . . . . . 20
3. Presentation Language . . . . . . . . . . . . . . . . . . . . 21 3. Presentation Language . . . . . . . . . . . . . . . . . . . . 22
3.1. Basic Block Size . . . . . . . . . . . . . . . . . . . . 21 3.1. Basic Block Size . . . . . . . . . . . . . . . . . . . . 22
3.2. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 21 3.2. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 22
3.3. Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.3. Vectors . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.5. Enumerateds . . . . . . . . . . . . . . . . . . . . . . . 23 3.5. Enumerateds . . . . . . . . . . . . . . . . . . . . . . . 24
3.6. Constructed Types . . . . . . . . . . . . . . . . . . . . 24 3.6. Constructed Types . . . . . . . . . . . . . . . . . . . . 25
3.7. Constants . . . . . . . . . . . . . . . . . . . . . . . . 24 3.7. Constants . . . . . . . . . . . . . . . . . . . . . . . . 25
3.8. Variants . . . . . . . . . . . . . . . . . . . . . . . . 24 3.8. Variants . . . . . . . . . . . . . . . . . . . . . . . . 25
3.9. Decoding Errors . . . . . . . . . . . . . . . . . . . . . 26 3.9. Decoding Errors . . . . . . . . . . . . . . . . . . . . . 26
4. Handshake Protocol . . . . . . . . . . . . . . . . . . . . . 26 4. Handshake Protocol . . . . . . . . . . . . . . . . . . . . . 27
4.1. Key Exchange Messages . . . . . . . . . . . . . . . . . . 27 4.1. Key Exchange Messages . . . . . . . . . . . . . . . . . . 28
4.1.1. Cryptographic Negotiation . . . . . . . . . . . . . . 28 4.1.1. Cryptographic Negotiation . . . . . . . . . . . . . . 28
4.1.2. Client Hello . . . . . . . . . . . . . . . . . . . . 29 4.1.2. Client Hello . . . . . . . . . . . . . . . . . . . . 29
4.1.3. Server Hello . . . . . . . . . . . . . . . . . . . . 31 4.1.3. Server Hello . . . . . . . . . . . . . . . . . . . . 32
4.1.4. Hello Retry Request . . . . . . . . . . . . . . . . . 33 4.1.4. Hello Retry Request . . . . . . . . . . . . . . . . . 34
4.2. Extensions . . . . . . . . . . . . . . . . . . . . . . . 34 4.2. Extensions . . . . . . . . . . . . . . . . . . . . . . . 35
4.2.1. Supported Versions . . . . . . . . . . . . . . . . . 36 4.2.1. Supported Versions . . . . . . . . . . . . . . . . . 38
4.2.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . 36 4.2.2. Cookie . . . . . . . . . . . . . . . . . . . . . . . 39
4.2.3. Signature Algorithms . . . . . . . . . . . . . . . . 37 4.2.3. Signature Algorithms . . . . . . . . . . . . . . . . 39
4.2.4. Negotiated Groups . . . . . . . . . . . . . . . . . . 40 4.2.4. Negotiated Groups . . . . . . . . . . . . . . . . . . 42
4.2.5. Key Share . . . . . . . . . . . . . . . . . . . . . . 41 4.2.5. Key Share . . . . . . . . . . . . . . . . . . . . . . 44
4.2.6. Pre-Shared Key Extension . . . . . . . . . . . . . . 44 4.2.6. Pre-Shared Key Exchange Modes . . . . . . . . . . . . 47
4.2.7. Pre-Shared Key Exchange Modes . . . . . . . . . . . . 46 4.2.7. Early Data Indication . . . . . . . . . . . . . . . . 47
4.2.8. Early Data Indication . . . . . . . . . . . . . . . . 47 4.2.8. Pre-Shared Key Extension . . . . . . . . . . . . . . 50
4.3. Server Parameters . . . . . . . . . . . . . . . . . . . . 50 4.3. Server Parameters . . . . . . . . . . . . . . . . . . . . 54
4.3.1. Encrypted Extensions . . . . . . . . . . . . . . . . 50 4.3.1. Encrypted Extensions . . . . . . . . . . . . . . . . 54
4.3.2. Certificate Request . . . . . . . . . . . . . . . . . 50 4.3.2. Certificate Request . . . . . . . . . . . . . . . . . 54
4.4. Authentication Messages . . . . . . . . . . . . . . . . . 52 4.4. Authentication Messages . . . . . . . . . . . . . . . . . 56
4.4.1. Certificate . . . . . . . . . . . . . . . . . . . . . 53 4.4.1. The Transcript Hash . . . . . . . . . . . . . . . . . 57
4.4.2. Certificate Verify . . . . . . . . . . . . . . . . . 57 4.4.2. Certificate . . . . . . . . . . . . . . . . . . . . . 58
4.4.3. Finished . . . . . . . . . . . . . . . . . . . . . . 59 4.4.3. Certificate Verify . . . . . . . . . . . . . . . . . 62
4.5. Post-Handshake Messages . . . . . . . . . . . . . . . . . 60 4.4.4. Finished . . . . . . . . . . . . . . . . . . . . . . 64
4.5.1. New Session Ticket Message . . . . . . . . . . . . . 61 4.5. End of Early Data . . . . . . . . . . . . . . . . . . . . 65
4.5.2. Post-Handshake Authentication . . . . . . . . . . . . 62 4.6. Post-Handshake Messages . . . . . . . . . . . . . . . . . 66
4.5.3. Key and IV Update . . . . . . . . . . . . . . . . . . 63 4.6.1. New Session Ticket Message . . . . . . . . . . . . . 66
4.6. Handshake Layer and Key Changes . . . . . . . . . . . . . 64 4.6.2. Post-Handshake Authentication . . . . . . . . . . . . 67
5. Record Protocol . . . . . . . . . . . . . . . . . . . . . . . 64 4.6.3. Key and IV Update . . . . . . . . . . . . . . . . . . 68
5.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 64 5. Record Protocol . . . . . . . . . . . . . . . . . . . . . . . 69
5.2. Record Payload Protection . . . . . . . . . . . . . . . . 66 5.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 69
5.3. Per-Record Nonce . . . . . . . . . . . . . . . . . . . . 68 5.2. Record Payload Protection . . . . . . . . . . . . . . . . 71
5.4. Record Padding . . . . . . . . . . . . . . . . . . . . . 68 5.3. Per-Record Nonce . . . . . . . . . . . . . . . . . . . . 73
5.5. Limits on Key Usage . . . . . . . . . . . . . . . . . . . 69 5.4. Record Padding . . . . . . . . . . . . . . . . . . . . . 74
6. Alert Protocol . . . . . . . . . . . . . . . . . . . . . . . 70 5.5. Limits on Key Usage . . . . . . . . . . . . . . . . . . . 75
6.1. Closure Alerts . . . . . . . . . . . . . . . . . . . . . 71 6. Alert Protocol . . . . . . . . . . . . . . . . . . . . . . . 75
6.2. Error Alerts . . . . . . . . . . . . . . . . . . . . . . 73 6.1. Closure Alerts . . . . . . . . . . . . . . . . . . . . . 76
7. Cryptographic Computations . . . . . . . . . . . . . . . . . 75 6.2. Error Alerts . . . . . . . . . . . . . . . . . . . . . . 77
7.1. Key Schedule . . . . . . . . . . . . . . . . . . . . . . 75 7. Cryptographic Computations . . . . . . . . . . . . . . . . . 80
7.2. Updating Traffic Keys and IVs . . . . . . . . . . . . . . 78 7.1. Key Schedule . . . . . . . . . . . . . . . . . . . . . . 80
7.3. Traffic Key Calculation . . . . . . . . . . . . . . . . . 78 7.2. Updating Traffic Keys and IVs . . . . . . . . . . . . . . 83
7.3.1. Diffie-Hellman . . . . . . . . . . . . . . . . . . . 79 7.3. Traffic Key Calculation . . . . . . . . . . . . . . . . . 84
7.3.2. Elliptic Curve Diffie-Hellman . . . . . . . . . . . . 79 7.4. (EC)DHE Shared Secret Calculation . . . . . . . . . . . . 84
7.3.3. Exporters . . . . . . . . . . . . . . . . . . . . . . 80 7.4.1. Finite Field Diffie-Hellman . . . . . . . . . . . . . 84
8. Compliance Requirements . . . . . . . . . . . . . . . . . . . 81 7.4.2. Elliptic Curve Diffie-Hellman . . . . . . . . . . . . 85
8.1. MTI Cipher Suites . . . . . . . . . . . . . . . . . . . . 81 7.5. Exporters . . . . . . . . . . . . . . . . . . . . . . . . 85
8.2. MTI Extensions . . . . . . . . . . . . . . . . . . . . . 81 8. Compliance Requirements . . . . . . . . . . . . . . . . . . . 86
9. Security Considerations . . . . . . . . . . . . . . . . . . . 82 8.1. Mandatory-to-Implement Cipher Suites . . . . . . . . . . 86
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 82 8.2. Mandatory-to-Implement Extensions . . . . . . . . . . . . 86
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 86 9. Security Considerations . . . . . . . . . . . . . . . . . . . 88
11.1. Normative References . . . . . . . . . . . . . . . . . . 86 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 88
11.2. Informative References . . . . . . . . . . . . . . . . . 88 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 89
Appendix A. Protocol Data Structures and Constant Values . . . . 94 11.1. Normative References . . . . . . . . . . . . . . . . . . 89
A.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 94 11.2. Informative References . . . . . . . . . . . . . . . . . 91
A.2. Alert Messages . . . . . . . . . . . . . . . . . . . . . 94 Appendix A. State Machine . . . . . . . . . . . . . . . . . . . 98
A.3. Handshake Protocol . . . . . . . . . . . . . . . . . . . 96 A.1. Client . . . . . . . . . . . . . . . . . . . . . . . . . 98
A.3.1. Key Exchange Messages . . . . . . . . . . . . . . . . 96 A.2. Server . . . . . . . . . . . . . . . . . . . . . . . . . 98
A.3.2. Server Parameters Messages . . . . . . . . . . . . . 100 Appendix B. Protocol Data Structures and Constant Values . . . . 99
A.3.3. Authentication Messages . . . . . . . . . . . . . . . 101 B.1. Record Layer . . . . . . . . . . . . . . . . . . . . . . 99
A.3.4. Ticket Establishment . . . . . . . . . . . . . . . . 101 B.2. Alert Messages . . . . . . . . . . . . . . . . . . . . . 100
A.3.5. Updating Keys . . . . . . . . . . . . . . . . . . . . 102 B.3. Handshake Protocol . . . . . . . . . . . . . . . . . . . 102
B.3.1. Key Exchange Messages . . . . . . . . . . . . . . . . 102
A.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 102 B.3.2. Server Parameters Messages . . . . . . . . . . . . . 107
Appendix B. Implementation Notes . . . . . . . . . . . . . . . . 103 B.3.3. Authentication Messages . . . . . . . . . . . . . . . 108
B.1. API considerations for 0-RTT . . . . . . . . . . . . . . 103 B.3.4. Ticket Establishment . . . . . . . . . . . . . . . . 109
B.2. Random Number Generation and Seeding . . . . . . . . . . 103 B.3.5. Updating Keys . . . . . . . . . . . . . . . . . . . . 109
B.3. Certificates and Authentication . . . . . . . . . . . . . 104 B.4. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 109
B.4. Implementation Pitfalls . . . . . . . . . . . . . . . . . 104 Appendix C. Implementation Notes . . . . . . . . . . . . . . . . 110
B.5. Client Tracking Prevention . . . . . . . . . . . . . . . 105 C.1. API considerations for 0-RTT . . . . . . . . . . . . . . 110
B.6. Unauthenticated Operation . . . . . . . . . . . . . . . . 106 C.2. Random Number Generation and Seeding . . . . . . . . . . 111
Appendix C. Backward Compatibility . . . . . . . . . . . . . . . 106 C.3. Certificates and Authentication . . . . . . . . . . . . . 111
C.1. Negotiating with an older server . . . . . . . . . . . . 107 C.4. Implementation Pitfalls . . . . . . . . . . . . . . . . . 111
C.2. Negotiating with an older client . . . . . . . . . . . . 108 C.5. Client Tracking Prevention . . . . . . . . . . . . . . . 113
C.3. Zero-RTT backwards compatibility . . . . . . . . . . . . 108 C.6. Unauthenticated Operation . . . . . . . . . . . . . . . . 113
C.4. Backwards Compatibility Security Restrictions . . . . . . 108 Appendix D. Backward Compatibility . . . . . . . . . . . . . . . 113
Appendix D. Overview of Security Properties . . . . . . . . . . 109 D.1. Negotiating with an older server . . . . . . . . . . . . 114
D.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 110 D.2. Negotiating with an older client . . . . . . . . . . . . 115
D.2. Record Layer . . . . . . . . . . . . . . . . . . . . . . 112 D.3. Zero-RTT backwards compatibility . . . . . . . . . . . . 115
Appendix E. Working Group Information . . . . . . . . . . . . . 114 D.4. Backwards Compatibility Security Restrictions . . . . . . 116
Appendix F. Contributors . . . . . . . . . . . . . . . . . . . . 114 Appendix E. Overview of Security Properties . . . . . . . . . . 116
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 118 E.1. Handshake . . . . . . . . . . . . . . . . . . . . . . . . 117
E.2. Record Layer . . . . . . . . . . . . . . . . . . . . . . 120
Appendix F. Working Group Information . . . . . . . . . . . . . 121
Appendix G. Contributors . . . . . . . . . . . . . . . . . . . . 122
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 127
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 key (PSK).
- Confidentiality: Data sent over the channel is not visible to - Confidentiality: Data sent over the channel is only visible to the
attackers. endpoints. TLS does not hide the length of the data it transmits,
though endpoints are able to pad in order to obscure lengths.
- 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 E 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) that 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
skipping to change at page 6, line 6 skipping to change at page 6, line 12
The following terms are used: The following terms are used:
client: The endpoint initiating the TLS connection. client: The endpoint initiating the TLS connection.
connection: A transport-layer connection between two endpoints. connection: A transport-layer connection between two endpoints.
endpoint: Either the client or server of the connection. endpoint: Either the client or server of the connection.
handshake: An initial negotiation between client and server that handshake: An initial negotiation between client and server that
establishes the parameters of their transactions. establishes the parameters of their subsequent interactions.
peer: An endpoint. When discussing a particular endpoint, "peer" peer: An endpoint. When discussing a particular endpoint, "peer"
refers to the endpoint that is remote to the primary subject of refers to the endpoint that is not the primary subject of discussion.
discussion.
receiver: An endpoint that is receiving records. receiver: An endpoint that is receiving records.
sender: An endpoint that is transmitting records. sender: An endpoint that is transmitting records.
session: An association between a client and a server resulting from
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-19
- Hash context_value input to Exporters (*)
- Add an additional Derive-Secret stage to Exporters (*).
- Hash ClientHello1 in the transcript when HRR is used. This
reduces the state that needs to be carried in cookies. (*)
- Restructure CertificateRequest to have the selectors in
extensions. This also allowed defining a
"certificate_authorities" extension which can be used by the
client instead of trusted_ca_keys (*).
- Tighten record framing requirements and require checking of them
(*).
- Consolidate "ticket_early_data_info" and "early_data" into a
single extension (*).
- Change end_of_early_data to be a handshake message (*).
- Add pre-extract Derive-Secret stages to key schedule (*).
- Remove spurious requirement to implement "pre_shared_key".
- Clarify location of "early_data" from server (it goes in EE, as
indicated by the table in S 10).
- Require peer public key validation
- Add state machine diagram.
draft-18 draft-18
- Remove unnecessary resumption_psk which is the only thing expanded - Remove unnecessary resumption_psk which is the only thing expanded
from the resumption master secret. (*). from the resumption master secret. (*).
- Fix signature_algorithms entry in extensions table. - Fix signature_algorithms entry in extensions table.
- Restate rule from RFC 6066 that you can't resume unless SNI is the - Restate rule from RFC 6066 that you can't resume unless SNI is the
same. same.
draft-17 draft-17
- Remove the 0-RTT Finished, resumption_context, and replace with a - Remove 0-RTT Finished and resumption_context, and replace with a
psk_binder field in the PSK itself (*) psk_binder field in the PSK itself (*)
- Restructure PSK key exchange negotiation modes (*) - Restructure PSK key exchange negotiation modes (*)
- Add max_early_data_size field to TicketEarlyDataInfo (*) - Add max_early_data_size field to TicketEarlyDataInfo (*)
- Add a 0-RTT exporter and change the transcript for the regular - Add a 0-RTT exporter and change the transcript for the regular
exporter (*) exporter (*)
- Merge TicketExtensions and Extensions registry. Changes - Merge TicketExtensions and Extensions registry. Changes
skipping to change at page 7, line 17 skipping to change at page 8, line 4
you need to match KDF but for 0-RTT you need whole cipher suite. you need to match KDF but for 0-RTT you need whole cipher suite.
This allows PSKs to actually negotiate cipher suites. (*) This allows PSKs to actually negotiate cipher suites. (*)
- Move SCT and OCSP into Certificate.extensions (*) - Move SCT and OCSP into Certificate.extensions (*)
- Explicitly allow non-offered extensions in NewSessionTicket - Explicitly allow non-offered extensions in NewSessionTicket
- Explicitly allow predicting ClientFinished for NST - Explicitly allow predicting ClientFinished for NST
- Clarify conditions for allowing 0-RTT with PSK - Clarify conditions for allowing 0-RTT with PSK
draft-16
- Revise version negotiation (*) - Revise version negotiation (*)
- Change RSASSA-PSS and EdDSA SignatureScheme codepoints for better - Change RSASSA-PSS and EdDSA SignatureScheme codepoints for better
backwards compatibility (*) backwards compatibility (*)
- Move HelloRetryRequest.selected_group to an extension (*) - Move HelloRetryRequest.selected_group to an extension (*)
- Clarify the behavior of no exporter context and make it the same - Clarify the behavior of no exporter context and make it the same
as an empty context.(*) as an empty context.(*)
skipping to change at page 11, line 5 skipping to change at page 11, line 41
- Change HKDF labeling to include protocol version and value - Change HKDF labeling to include protocol version and value
lengths. lengths.
- Shift the final decision to abort a handshake due to incompatible - Shift the final decision to abort a handshake due to incompatible
certificates to the client rather than having servers abort early. certificates to the client rather than having servers abort early.
- Deprecate SHA-1 with signatures. - Deprecate SHA-1 with signatures.
- Add MTI algorithms. - Add MTI algorithms.
draft-08
- Remove support for weak and lesser used named curves. - Remove support for weak and lesser used named curves.
- Remove support for MD5 and SHA-224 hashes with signatures. - Remove support for MD5 and SHA-224 hashes with signatures.
- Update lists of available AEAD cipher suites and error alerts. - Update lists of available AEAD cipher suites and error alerts.
- Reduce maximum permitted record expansion for AEAD from 2048 to - Reduce maximum permitted record expansion for AEAD from 2048 to
256 octets. 256 octets.
- Require digital signatures even when a previous configuration is - Require digital signatures even when a previous configuration is
skipping to change at page 13, line 16 skipping to change at page 14, line 7
Section 4.1.3. Section 4.1.3.
- RSASSA-PSS signature schemes are defined in Section 4.2.3. - 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 connection state are produced by
TLS handshake protocol, which a TLS client and server use when first the TLS handshake protocol, which a TLS client and server use when
communicating to agree on a protocol version, select cryptographic first communicating to agree on a protocol version, select
algorithms, optionally authenticate each other, and establish shared cryptographic algorithms, optionally authenticate each other, and
secret keying material. Once the handshake is complete, the peers establish shared secret keying material. Once the handshake is
use the established keys to protect application layer traffic. complete, the peers use the established keys to protect application
layer traffic.
A failure of the handshake or other protocol error triggers the A failure of the handshake or other protocol error triggers the
termination of the connection, optionally preceded by an alert termination of the connection, optionally preceded by an alert
message (Section 6). message (Section 6).
TLS supports three basic key exchange modes: TLS supports three basic key exchange modes:
- Diffie-Hellman (both the finite field and elliptic curve - (EC)DHE (Diffie-Hellman both the finite field and elliptic curve
varieties), varieties),
- A pre-shared symmetric key (PSK), and - PSK-only, and
- A combination of PSK and Diffie-Hellman. - PSK with (EC)DHE
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*
| + pre_shared_key_modes* | + psk_key_exchange_modes*
v + pre_shared_key* --------> v + pre_shared_key* -------->
ServerHello ^ Key ServerHello ^ Key
+ key_share* | Exch + key_share* | Exch
+ pre_shared_key* v + pre_shared_key* v
{EncryptedExtensions} ^ Server {EncryptedExtensions} ^ Server
{CertificateRequest*} v Params {CertificateRequest*} v Params
{Certificate*} ^ {Certificate*} ^
{CertificateVerify*} | Auth {CertificateVerify*} | Auth
{Finished} v {Finished} v
<-------- [Application Data*] <-------- [Application Data*]
^ {Certificate*} ^ {Certificate*}
Auth | {CertificateVerify*} Auth | {CertificateVerify*}
v {Finished} --------> v {Finished} -------->
[Application Data] <-------> [Application Data] [Application Data] <-------> [Application Data]
+ Indicates extensions sent in the + Indicates noteworthy extensions sent in the
previously noted message. previously noted message.
* Indicates optional or situation-dependent * Indicates optional or situation-dependent
messages/extensions that are not always sent. messages/extensions that are not always sent.
{} Indicates messages protected using keys {} Indicates messages protected using keys
derived from handshake_traffic_secret. derived from a [sender]_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
skipping to change at page 15, line 10 skipping to change at page 16, line 10
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 versions; 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 4.2.5), a set of pre- shares (in the "key_share" extension Section 4.2.5), a set of pre-
shared key labels (in the "pre_shared_key" extension Section 4.2.6) shared key labels (in the "pre_shared_key" extension Section 4.2.8)
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 (Section 4.1.3), which indicates the negotiated
parameters. [Section 4.1.3]. The combination of the ClientHello and connection parameters. The combination of the ClientHello and the
the ServerHello determines the shared keys. If (EC)DHE key ServerHello determines the shared keys. If (EC)DHE key establishment
establishment is in use, then the ServerHello contains a "key_share" is in use, then the ServerHello contains a "key_share" extension with
extension with the server's ephemeral Diffie-Hellman share which MUST the server's ephemeral Diffie-Hellman share which MUST be in the same
be in the same group as one of the client's shares. If PSK key group as one of the client's shares. If PSK key establishment is in
establishment is in use, then the ServerHello contains a use, then the ServerHello contains a "pre_shared_key" extension
"pre_shared_key" extension indicating which of the client's offered indicating which of the client's offered PSKs was selected. Note
PSKs was selected. Note that implementations can use (EC)DHE and PSK that implementations can use (EC)DHE and PSK together, in which case
together, in which case both extensions will be supplied. 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 that are not EncryptedExtensions: responses to any extensions that are not
required to determine the cryptographic parameters, other than required to determine the cryptographic parameters, other than
those that are specific to individual certificates. those that are specific to individual certificates.
[Section 4.3.1] [Section 4.3.1]
CertificateRequest: if certificate-based client authentication is CertificateRequest: if certificate-based client authentication is
skipping to change at page 15, line 51 skipping to change at page 16, line 51
needed. Specifically: needed. Specifically:
Certificate: the certificate of the endpoint and any per-certificate Certificate: the certificate of the endpoint and any per-certificate
extensions. This message is omitted by the server if not extensions. This message is omitted by the server if not
authenticating with a certificate and by the client if the server authenticating with a certificate and by the client if the server
did not send CertificateRequest (thus indicating that the client did not send CertificateRequest (thus indicating that the client
should not authenticate with a certificate). Note that if raw should not authenticate with a certificate). Note that if raw
public keys [RFC7250] or the cached information extension public keys [RFC7250] or the cached information extension
[RFC7924] are in use, then this message will not contain a [RFC7924] are in use, then this message will not contain a
certificate but rather some other value corresponding to the certificate but rather some other value corresponding to the
server's long-term key. [Section 4.4.1] server's long-term key. [Section 4.4.2]
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 private key corresponding to the public key in the Certificate
the endpoint is not authenticating via a certificate. message. This message is omitted if the endpoint is not
[Section 4.4.2] authenticating via a certificate. [Section 4.4.3]
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 4.4.3] authenticates the handshake. [Section 4.4.4]
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 to 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 needs to restart the handshake with HelloRetryRequest and the client needs to restart the handshake with
an appropriate "key_share" extension, as shown in Figure 2. If no an appropriate "key_share" extension, as shown in Figure 2. If no
common cryptographic parameters can be negotiated, the server MUST common cryptographic parameters can be negotiated, the server MUST
abort the handshake with an appropriate alert. abort the handshake with an appropriate alert.
Client Server Client Server
ClientHello ClientHello
+ key_share --------> + key_share -------->
<-------- HelloRetryRequest <-------- HelloRetryRequest
+ key_share + key_share
ClientHello ClientHello
+ key_share --------> + key_share -------->
ServerHello ServerHello
+ key_share + key_share
{EncryptedExtensions} {EncryptedExtensions}
{CertificateRequest*} {CertificateRequest*}
{Certificate*} {Certificate*}
{CertificateVerify*} {CertificateVerify*}
{Finished} {Finished}
<-------- [Application Data*] <-------- [Application Data*]
{Certificate*} {Certificate*}
{CertificateVerify*} {CertificateVerify*}
{Finished} --------> {Finished} -------->
[Application Data] <-------> [Application Data] [Application Data] <-------> [Application Data]
Figure 2: Message flow for a full handshake with mismatched Figure 2: Message flow for a full handshake with mismatched
parameters parameters
Note: The handshake transcript includes the initial ClientHello/ Note: The handshake transcript includes the initial ClientHello/
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 connection 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 that corresponds to a key derived from the the client a PSK identity that corresponds to a key derived from the
initial handshake (see Section 4.5.1). The client can then use that initial handshake (see Section 4.6.1). 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 and the key derived
this functionality was provided by "session IDs" and "session from the initial handshake is used to bootstrap the cryptographic
tickets" [RFC5077]. Both mechanisms are obsoleted in TLS 1.3. state instead of a full handshake. In TLS 1.2 and below, this
functionality was provided by "session IDs" and "session 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 key exchange in order to provide
secrecy in combination with shared keys, or can be used alone, at the forward secrecy in combination with shared keys, or can be used
cost of losing forward secrecy. alone, at the cost of losing forward secrecy.
Figure 3 shows a pair of handshakes in which the first establishes a Figure 3 shows a pair of handshakes in which the first establishes a
PSK and the second uses it: PSK and the second uses it:
Client Server Client Server
Initial Handshake: Initial Handshake:
ClientHello ClientHello
+ key_share --------> + key_share -------->
ServerHello ServerHello
skipping to change at page 18, line 31 skipping to change at page 19, line 35
{Certificate*} {Certificate*}
{CertificateVerify*} {CertificateVerify*}
{Finished} --------> {Finished} -------->
<-------- [NewSessionTicket] <-------- [NewSessionTicket]
[Application Data] <-------> [Application Data] [Application Data] <-------> [Application Data]
Subsequent Handshake: Subsequent Handshake:
ClientHello ClientHello
+ key_share* + key_share*
+ psk_key_exchange_modes + psk_key_exchange_modes
+ pre_shared_key --------> + pre_shared_key -------->
ServerHello ServerHello
+ pre_shared_key + pre_shared_key
+ 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 message. When a client offers Certificate or a CertificateVerify message. When a client offers
resumption via PSK, it SHOULD also supply a "key_share" extension to resumption via PSK, it SHOULD also supply a "key_share" extension to
the server as well to allow the server to decline resumption and fall the server to allow the server to decline resumption and fall back to
back to a full handshake, if needed. The server responds with a 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.
When PSKs are provisioned out of band, the PSK identity and the KDF When PSKs are provisioned out of band, the PSK identity and the KDF
to be used with the PSK MUST also be provisioned. to be used with the PSK MUST also be provisioned.
2.3. Zero-RTT Data 2.3. Zero-RTT Data
When clients and servers share a PSK (either obtained out-of-band or When clients and servers share a PSK (either obtained externally or
via a previous handshake), TLS 1.3 allows clients to send data on the via a previous handshake), TLS 1.3 allows clients to send data on the
first flight ("early data"). The client uses the PSK to authenticate first flight ("early data"). The client uses the PSK to authenticate
the server and to encrypt the early data. the server and to encrypt the early data.
When clients use a PSK obtained out-of-band then the following When clients use a PSK obtained externally then the following
additional information MUST be provisioned to both parties: additional information MUST be provisioned to both parties:
- The cipher suite for use with this PSK - The cipher suite for use with this PSK
- The Application-Layer Protocol Negotiation (ALPN) protocol, if any - The Application-Layer Protocol Negotiation (ALPN) protocol, if any
is to be used is to be used
- The Server Name Indication (SNI), if any is to be used - The Server Name Indication (SNI), if any is to be used
As shown in Figure 4, the Zero-RTT data is just added to the 1-RTT As shown in Figure 4, the 0-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 as with a 1-RTT handshake with PSK resumption. same messages as with a 1-RTT handshake with PSK resumption.
Client Server Client Server
ClientHello ClientHello
+ early_data + early_data
+ key_share* + key_share*
+ pre_shared_key_modes + psk_key_exchange_modes
+ pre_shared_key + pre_shared_key
(Application Data*) (Application Data*) -------->
(end_of_early_data) -------->
ServerHello ServerHello
+ early_data
+ pre_shared_key + pre_shared_key
+ key_share* + key_share*
{EncryptedExtensions} {EncryptedExtensions}
{Finished} {Finished}
<-------- [Application Data*] <-------- [Application Data*]
{Finished} --------> (EndOfEarlyData)
{Finished} -------->
[Application Data] <-------> [Application Data] [Application Data] <-------> [Application Data]
* Indicates optional or situation-dependent * Indicates optional or situation-dependent
messages/extensions that are not always sent. messages/extensions that are not always sent.
() Indicates messages protected using keys () Indicates messages protected using keys
derived from client_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 a [sender]_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
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, as it is encrypted solely under 1. This data is not forward secret, as it is encrypted solely under
keys derived using the offered PSK. keys derived using the offered 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 4.2.8.2 for more details). This is especially relevant Section 4.2.8.3 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.)
Protocols MUST NOT use 0-RTT data without a profile that defines its Protocols MUST NOT use 0-RTT data without a profile that defines its
use. That profile needs to identify which messages or interactions use. That profile needs to identify which messages or interactions
are safe to use with 0-RTT. In addition, to avoid accidental misuse, are safe to use with 0-RTT. In addition, to avoid accidental misuse,
implementations SHOULD NOT enable 0-RTT unless specifically implementations SHOULD NOT enable 0-RTT unless specifically
requested. Special functions for 0-RTT data are RECOMMENDED to requested. Implementations SHOULD provide special functions for
ensure that an application is always aware that it is sending or 0-RTT data to ensure that an application is always aware that it is
receiving data that might be replayed. sending or receiving data that might be replayed.
The same warnings apply to any use of the early exporter secret. The same warnings apply to any use of the early_exporter_secret.
The remainder of this document provides a detailed description of The remainder of this document provides a detailed description of
TLS. TLS.
3. Presentation Language 3. Presentation Language
This document deals with the formatting of data in an external This document deals with the formatting of data in an external
representation. The following very basic and somewhat casually representation. The following very basic and somewhat casually
defined presentation syntax will be used. defined presentation syntax will be used.
skipping to change at page 22, line 25 skipping to change at page 23, line 25
Here, T' occupies n bytes in the data stream, where n is a multiple Here, T' occupies n bytes in the data stream, where n is a multiple
of the size of T. The length of the vector is not included in the of the size of T. The length of the vector is not included in the
encoded stream. encoded stream.
In the following example, Datum is defined to be three consecutive In the following example, Datum is defined to be three consecutive
bytes that the protocol does not interpret, while Data is three bytes that the protocol does not interpret, while Data is three
consecutive Datum, consuming a total of nine bytes. consecutive Datum, consuming a total of nine bytes.
opaque Datum[3]; /* three uninterpreted bytes */ opaque Datum[3]; /* three uninterpreted bytes */
Datum Data[9]; /* 3 consecutive 3 byte vectors */ Datum Data[9]; /* 3 consecutive 3-byte vectors */
Variable-length vectors are defined by specifying a subrange of legal Variable-length vectors are defined by specifying a subrange of legal
lengths, inclusively, using the notation <floor..ceiling>. When lengths, inclusively, using the notation <floor..ceiling>. When
these are encoded, the actual length precedes the vector's contents these are encoded, the actual length precedes the vector's contents
in the byte stream. The length will be in the form of a number in the byte stream. The length will be in the form of a number
consuming as many bytes as required to hold the vector's specified consuming as many bytes as required to hold the vector's specified
maximum (ceiling) length. A variable-length vector with an actual maximum (ceiling) length. A variable-length vector with an actual
length field of zero is referred to as an empty vector. length field of zero is referred to as an empty vector.
T T'<floor..ceiling>; T T'<floor..ceiling>;
skipping to change at page 23, line 32 skipping to change at page 24, line 32
An additional sparse data type is available called enum. Each An additional sparse data type is available called enum. Each
definition is a different type. Only enumerateds of the same type definition is a different type. Only enumerateds of the same type
may be assigned or compared. Every element of an enumerated must be may be assigned or compared. Every element of an enumerated must be
assigned a value, as demonstrated in the following example. Since assigned a value, as demonstrated in the following example. Since
the elements of the enumerated are not ordered, they can be assigned the elements of the enumerated are not ordered, they can be assigned
any unique value, in any order. any unique value, in any order.
enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te; enum { e1(v1), e2(v2), ... , en(vn) [[, (n)]] } Te;
Future extension or additions to the protocol may define new values. Future extensions or additions to the protocol may define new values.
Implementations need to be able to parse and ignore unknown values Implementations need to be able to parse and ignore unknown values
unless the definition of the field states otherwise. unless the definition of the field states otherwise.
An enumerated occupies as much space in the byte stream as would its An enumerated occupies as much space in the byte stream as would its
maximal defined ordinal value. The following definition would cause maximal defined ordinal value. The following definition would cause
one byte to be used to carry fields of type Color. one byte to be used to carry fields of type Color.
enum { red(3), blue(5), white(7) } Color; enum { red(3), blue(5), white(7) } Color;
One may optionally specify a value without its associated tag to One may optionally specify a value without its associated tag to
force the width definition without defining a superfluous element. force the width definition without defining a superfluous element.
In the following example, Taste will consume two bytes in the data In the following example, Taste will consume two bytes in the data
stream but can only assume the values 1, 2, or 4 in current version stream but can only assume the values 1, 2, or 4 in the current
of protocol. version of the protocol.
enum { sweet(1), sour(2), bitter(4), (32000) } Taste; enum { sweet(1), sour(2), bitter(4), (32000) } Taste;
The names of the elements of an enumeration are scoped within the The names of the elements of an enumeration are scoped within the
defined type. In the first example, a fully qualified reference to defined type. In the first example, a fully qualified reference to
the second element of the enumeration would be Color.blue. Such the second element of the enumeration would be Color.blue. Such
qualification is not required if the target of the assignment is well qualification is not required if the target of the assignment is well
specified. specified.
Color color = Color.blue; /* overspecified, legal */ Color color = Color.blue; /* overspecified, legal */
skipping to change at page 24, line 51 skipping to change at page 25, line 51
struct { struct {
T1 f1 = 8; /* T.f1 must always be 8 */ T1 f1 = 8; /* T.f1 must always be 8 */
T2 f2; T2 f2;
} T; } T;
3.8. Variants 3.8. 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. The
must be a case arm for every element of the enumeration declared in body of the variant structure may be given a label for reference.
the select. Case arms have limited fall-through: if two case arms
follow in immediate succession with no fields in between, then they
both contain the same fields. Thus, in the example below, "orange"
and "banana" both contain V2. Note that this piece of syntax was
added in TLS 1.2 [RFC5246]. Each case arm can have one or more
fields.
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: Te21; case e2: Te2;
Te22;
case e3: case e4: Te3;
.... ....
case en: Ten; case en: Ten;
} [[fv]]; } [[fv]];
} [[Tv]]; } [[Tv]];
For example: For example:
enum { apple(0), orange(1), banana(2) } VariantTag; enum { apple(0), orange(1) } VariantTag;
struct { struct {
uint16 number; uint16 number;
opaque string<0..10>; /* variable length */ opaque string<0..10>; /* variable length */
} V1; } V1;
struct { struct {
uint32 number; uint32 number;
opaque string[10]; /* fixed length */ opaque string[10]; /* fixed length */
} V2; } V2;
struct { struct {
select (VariantTag) { VariantTag type;
case apple: select (VariantRecord.type) {
V1; /* VariantBody, tag = apple */ case apple: V1;
case orange: case orange: V2;
case banana: };
V2; /* VariantBody, tag = orange or banana */
} variant_body; /* optional label on variant */
} VariantRecord; } VariantRecord;
3.9. Decoding Errors 3.9. Decoding Errors
TLS defines two generic alerts (see Section 6) to use upon failure to TLS defines two generic alerts (see Section 6) to use upon failure to
parse a message. Peers which receive a message which cannot be parse a message. Peers which receive a message which cannot be
parsed according to the syntax (e.g., have a length extending beyond parsed according to the syntax (e.g., have a length extending beyond
the message boundary or contain an out-of-range length) MUST the message boundary or contain an out-of-range length) MUST
terminate the connection with a "decode_error" alert. Peers which terminate the connection with a "decode_error" alert. Peers which
receive a message which is syntactically correct but semantically receive a message which is syntactically correct but semantically
invalid (e.g., a DHE share of p - 1, or an invalid enum) MUST invalid (e.g., a DHE share of p - 1, or an invalid enum) MUST
terminate the connection with an "illegal_parameter" alert. 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 connection. Handshake messages are supplied to the TLS record
where they are encapsulated within one or more TLSPlaintext or layer, 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 connection state.
enum { enum {
client_hello(1), client_hello(1),
server_hello(2), server_hello(2),
new_session_ticket(4), new_session_ticket(4),
end_of_early_data(5),
hello_retry_request(6), hello_retry_request(6),
encrypted_extensions(8), encrypted_extensions(8),
certificate(11), certificate(11),
certificate_request(13), certificate_request(13),
certificate_verify(15), certificate_verify(15),
finished(20), finished(20),
key_update(24), key_update(24),
message_hash(254),
(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 (Handshake.msg_type) { select (Handshake.msg_type) {
case client_hello: ClientHello; case client_hello: ClientHello;
case server_hello: ServerHello; case server_hello: ServerHello;
case end_of_early_data: EndOfEarlyData;
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;
skipping to change at page 28, line 21 skipping to change at page 28, line 32
hash pairs which the client supports. hash pairs which the client supports.
- A "supported_groups" (Section 4.2.4) extension which indicates the - A "supported_groups" (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 4.2.5) 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 4.2.3) 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 4.2.6) extension which contains a list - A "pre_shared_key" (Section 4.2.8) extension which contains a list
of symmetric key identities known to the client and a of symmetric key identities known to the client and a
"psk_key_exchange_modes" (Section 4.2.7) extension which indicates "psk_key_exchange_modes" (Section 4.2.6) extension which indicates
the key exchange modes that may be used with PSKs. the key exchange modes that may be used with PSKs.
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 there is overlap in the "supported_groups" extension the client. If there is no overlap in "supported_groups" then the
but the client did not offer a compatible "key_share" extension, then
the server will respond with a HelloRetryRequest (Section 4.1.4)
message. If there is no overlap in "supported_groups" then the
server MUST abort the handshake. server MUST abort the handshake.
If the server selects a PSK, then it MUST also select a key If the server selects a PSK, then it MUST also select a key
establishment mode from the set indicated by client's establishment mode from the set indicated by client's
"psk_key_exchange_modes extension (PSK alone or with (EC)DHE). Note "psk_key_exchange_modes" extension (PSK alone or with (EC)DHE). Note
that if the PSK can be used without (EC)DHE then non-overlap in the that if the PSK can be used without (EC)DHE then non-overlap in the
"supported_groups" parameters need not be fatal. "supported_groups" parameters need not be fatal, as it is in the non-
PSK case discussed in the previous paragraph.
The server indicates its selected parameters in the ServerHello as If the server selects an (EC)DHE group and the client did not offer a
follows: compatible "key_share" extension in the initial ClientHello, the
server MUST respond with a HelloRetryRequest (Section 4.1.4) message.
- If PSK is being used then the server will send a "pre_shared_key" If the server successfully selects parameters and does not require a
HelloRetryRequest, it indicates the selected parameters in the
ServerHello as follows:
- If PSK is being used, then the server will send a "pre_shared_key"
extension indicating the selected key. extension indicating the selected key.
- If PSK is not being used, then (EC)DHE and certificate-based - If PSK is not being used, then (EC)DHE and certificate-based
authentication are always used. authentication are always used.
- When (EC)DHE is in use, the server will also provide a "key_share" - When (EC)DHE is in use, the server will also provide a "key_share"
extension. extension.
- When authenticating via a certificate (i.e., when a PSK is not in - When authenticating via a certificate, the server will send the
use), the server will send the Certificate (Section 4.4.1) and Certificate (Section 4.4.2) and CertificateVerify (Section 4.4.3)
CertificateVerify (Section 4.4.2) messages. messages. In TLS 1.3 as defined by this document, either a PSK or
a certificate is always used, but not both. Future documents may
define how to use them together.
If the server is unable to negotiate a supported set of parameters If the server is unable to negotiate a supported set of parameters
(i.e., there is no overlap between the client and server parameters), (i.e., there is no overlap between the client and server parameters),
it MUST abort the handshake with either a "handshake_failure" or it MUST abort the handshake with either a "handshake_failure" or
"insufficient_security" fatal alert (see Section 6). "insufficient_security" fatal alert (see Section 6).
4.1.2. Client Hello 4.1.2. Client Hello
When a client first connects to a server, it is REQUIRED to send the 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 ClientHello as its first message. The client will also send a
ClientHello when the server has responded to its ClientHello with a ClientHello when the server has responded to its ClientHello with a
HelloRetryRequest. In that case, the client MUST send the same HelloRetryRequest. In that case, the client MUST send the same
ClientHello (without modification) except: ClientHello (without modification) except:
- If a "key_share" extension was supplied in the HelloRetryRequest, - If a "key_share" extension was supplied in the HelloRetryRequest,
replacing the list of shares with a list containing a single replacing the list of shares with a list containing a single
KeyShareEntry from the indicated group. KeyShareEntry from the indicated group.
- Removing the "early_data" extension (Section 4.2.8) if one was - Removing the "early_data" extension (Section 4.2.7) if one was
present. Early data is not permitted after HelloRetryRequest. present. Early data is not permitted after HelloRetryRequest.
- Including a "cookie" extension if one was provided in the - Including a "cookie" extension if one was provided in the
HelloRetryRequest. HelloRetryRequest.
- Updating the "pre_shared_key" extension if present by recomputing
the "obfuscated_ticket_age" and binder values and (optionally)
removing any PSKs which are incompatible with the server's
indicated cipher suite.
Because TLS 1.3 forbids renegotiation, if a server receives a Because TLS 1.3 forbids renegotiation, if a server receives a
ClientHello at any other time, it MUST terminate the connection. ClientHello at any other time, it MUST terminate the connection.
If a server established a TLS connection with a previous version of 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 TLS and receives a TLS 1.3 ClientHello in a renegotiation, it MUST
retain the previous protocol version. In particular, it MUST NOT retain the previous protocol version. In particular, it MUST NOT
negotiate TLS 1.3. A client that receives a TLS 1.3 ServerHello negotiate TLS 1.3.
during renegotiation MUST abort the handshake with a
"protocol_version" alert.
Structure of this message: Structure of this message:
uint16 ProtocolVersion; uint16 ProtocolVersion;
opaque Random[32]; opaque Random[32];
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
struct { struct {
ProtocolVersion legacy_version = 0x0303; /* TLS v1.2 */ ProtocolVersion legacy_version = 0x0303; /* 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<8..2^16-1>;
} ClientHello; } ClientHello;
TLS allows extensions to follow the compression_methods field in an All versions of TLS allow extensions to optionally follow the
extensions block. The presence of extensions can be detected by compression_methods field as an extensions field. TLS 1.3
determining whether there are bytes following the compression_methods ClientHellos will contain at least two extensions,
at the end of the ClientHello. Note that this method of detecting "supported_versions" and either "key_share" or "pre_shared_key". The
optional data differs from the normal TLS method of having a presence of extensions can be detected by determining whether there
variable-length field, but it is used for compatibility with TLS are bytes following the compression_methods at the end of the
before extensions were defined. As of TLS 1.3, all clients and ClientHello. Note that this method of detecting optional data
servers will send at least one extension (at least "key_share" or differs from the normal TLS method of having a variable-length field,
"pre_shared_key"). but it is used for compatibility with TLS before extensions were
defined. TLS 1.3 servers will need to perform this check first and
only attempt to negotiate TLS 1.3 if a "supported_version" extension
is present.
legacy_version In previous versions of TLS, this field was used for legacy_version In previous versions of TLS, this field was used for
version negotiation and represented the highest version number version negotiation and represented the highest version number
supported by the client. Experience has shown that many servers supported by the client. Experience has shown that many servers
do not properly implement version negotiation, leading to "version do not properly implement version negotiation, leading to "version
intolerance" in which the server rejects an otherwise acceptable intolerance" in which the server rejects an otherwise acceptable
ClientHello with a version number higher than it supports. In TLS ClientHello with a version number higher than it supports. In TLS
1.3, the client indicates its version preferences in the 1.3, the client indicates its version preferences in the
"supported_versions" extension (Section 4.2.1) and this field MUST "supported_versions" extension (Section 4.2.1) and the
be set to 0x0303, which was the version number for TLS 1.2. (See legacy_version field MUST be set to 0x0303, which was the version
Appendix C for details about backward compatibility.) number for TLS 1.2. (See Appendix D 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 C 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
resumption feature which has been merged with Pre-Shared Keys in "session resumption" feature which has been merged with Pre-Shared
this version (see Section 2.2). This field MUST be ignored by a Keys in this version (see Section 2.2). This field MUST be
server negotiating TLS 1.3 and MUST be set as a zero length vector ignored by a server negotiating TLS 1.3 and MUST be set as a zero
(i.e., a single zero byte length field) by clients which do not length vector (i.e., a single zero byte length field) by clients
have a cached session ID set by a pre-TLS 1.3 server. which do not have a cached session ID set by a pre-TLS 1.3 server.
cipher_suites This is a list of the symmetric cipher options cipher_suites This is a list of the symmetric cipher options
supported by the client, specifically the record protection supported by the client, specifically the record protection
algorithm (including secret key length) and a hash to be used with algorithm (including secret key length) and a hash to be used with
HKDF, in descending order of client preference. If the list HKDF, in descending order of client preference. If the list
contains cipher suites the server does not recognize, support, or contains cipher suites the server does not recognize, support, or
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 B.4. If the client is attempting a PSK key
establishment, it SHOULD advertise at least one cipher suite
containing a Hash associated with the PSK.
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 abort the handshake with an "illegal_parameter" the server MUST abort the handshake with an "illegal_parameter"
alert. Note that TLS 1.3 servers might receive TLS 1.2 or prior alert. Note that TLS 1.3 servers might receive TLS 1.2 or prior
ClientHellos which contain other compression methods and MUST ClientHellos which contain other compression methods and MUST
follow the 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 TLS 1.3, use of certain
extensions is mandatory, as functionality is moved into extensions
to preserve ClientHello compatibility with previous versions of
TLS. Servers MUST ignore unrecognized extensions.
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 always contain extensions (minimally they must contain messages always contain extensions (minimally they must contain
"supported_versions" or they will be interpreted as TLS 1.2 "supported_versions" or they will be interpreted as TLS 1.2
ClientHello messages). TLS 1.3 servers may receive TLS 1.2 ClientHello messages). TLS 1.3 servers might receive ClientHello
ClientHello messages without extensions. If negotiating TLS 1.2, a messages from versions of TLS prior to 1.3 that do not contain
server MUST check that the message either contains no data after extensions. If negotiating a version of TLS prior to 1.3, a server
MUST check that the message either contains no data after
legacy_compression_methods or that it contains a valid extensions legacy_compression_methods or that it contains a valid extensions
block with no data following. If not, then it MUST abort the block with no data following. If not, then it MUST abort the
handshake with a "decode_error" alert. 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
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 and message if it is able to find an acceptable set of parameters and the
the client's "key_share" extension was acceptable. If it is not able ClientHello contains sufficient information to proceed with the
to find an acceptable set of parameters, the server will respond with handshake.
a "handshake_failure" fatal alert.
Structure of this message: Structure of this message:
struct { struct {
ProtocolVersion version; ProtocolVersion version;
Random random; Random random;
CipherSuite cipher_suite; CipherSuite cipher_suite;
Extension extensions<0..2^16-1>; Extension extensions<6..2^16-1>;
} ServerHello; } ServerHello;
version This field contains the version of TLS negotiated for this version This field contains the version of TLS negotiated for this
session. Servers MUST select a version from the list in connection. Servers MUST select a version from the list in
ClientHello.supported_versions extension. A client which receives ClientHello.supported_versions extension. A client which receives
a version that was not offered MUST abort the handshake. For this a version that was not offered MUST abort the handshake. For this
version of the specification, the version is 0x0304. (See version of the specification, the version is 0x0304. (See
Appendix C for details about backward compatibility.) Appendix D for details about backward compatibility.)
random This structure is generated by the server and MUST be random 32 bytes generated by a secure random number generator. See
Appendix C for additional information. The last eight bytes MUST
be overwritten as described below if negotiating TLS 1.2 or TLS
1.1. 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. A client which receives a list in ClientHello.cipher_suites. A client which receives a
cipher suite that was not offered MUST abort the handshake. cipher suite that was not offered MUST abort the handshake.
extensions A list of extensions. The ServerHello MUST only include extensions A list of extensions. 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" and context. Currently the only such extensions are "key_share" and
"pre_shared_key". "pre_shared_key". All current TLS 1.3 ServerHello messages will
contain one of these two extensions, or both when using a PSK with
(EC)DHE key establishment.
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 servers which negotiate TLS 1.2 or below in
ClientHello indicating only support for TLS 1.2 or below MUST set the response to a ClientHello MUST set the last eight bytes of their
last eight bytes of their Random value to the bytes: Random value specially.
If negotiating TLS 1.2, TLS 1.3 servers MUST set the 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 1.3 server implementations which respond to a ClientHello If negotiating TLS 1.1, TLS 1.3 servers MUST and TLS 1.2 servers
indicating only support for TLS 1.1 or below SHOULD set the last 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 bytes 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 check that the last eight bytes are not
indicates TLS 1.1 or below. If a match is found, the client MUST equal to the second value if the ServerHello indicates TLS 1.1 or
abort the handshake with an "illegal_parameter" alert. This below. If a match is found, the client MUST abort the handshake with
mechanism provides limited protection against downgrade attacks over an "illegal_parameter" alert. This mechanism provides limited
and above that provided by the Finished exchange: because the protection against downgrade attacks over and above that provided by
ServerKeyExchange includes a signature over both random values, it is the Finished exchange: because the ServerKeyExchange, a message
not possible for an active attacker to modify the randoms without present in TLS 1.2 and below, includes a signature over both random
detection as long as ephemeral ciphers are used. It does not provide values, it is not possible for an active attacker to modify the
downgrade protection when static RSA is used. random values without detection as long as ephemeral ciphers are
used. It does not provide 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 a change from [RFC5246], 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.
A client that receives a TLS 1.3 ServerHello during renegotiation
MUST abort the handshake with a "protocol_version" alert.
RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH Implementations of RFC EDITOR: PLEASE REMOVE THE FOLLOWING PARAGRAPH Implementations of
draft versions (see Section 4.2.1.1) of this specification SHOULD NOT draft versions (see Section 4.2.1.1) of this specification SHOULD NOT
implement this mechanism on either client and server. A pre-RFC implement this mechanism on either client and server. A pre-RFC
client connecting to RFC servers, or vice versa, will appear to client connecting to RFC servers, or vice versa, will appear to
downgrade to TLS 1.2. With the mechanism enabled, this will cause an downgrade to TLS 1.2. With the mechanism enabled, this will cause an
interoperability failure. interoperability failure.
4.1.4. Hello Retry Request 4.1.4. Hello Retry Request
Servers send this message in response to a ClientHello message if The server will send this message in response to a ClientHello
they were able to find an acceptable set of algorithms and groups message if it is able to find an acceptable set of parameters but the
that are mutually supported, but the client's ClientHello did not ClientHello does not contain sufficient information to proceed with
contain sufficient information to proceed with the handshake. If a the handshake.
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;
CipherSuite cipher_suite;
Extension extensions<2..2^16-1>; Extension extensions<2..2^16-1>;
} HelloRetryRequest; } HelloRetryRequest;
The version and extensions fields have the same meanings as their The version, cipher_suite, and extensions fields have the same
corresponding values in the ServerHello. The server SHOULD send only meanings as their corresponding values in the ServerHello. The
the extensions necessary for the client to generate a correct server SHOULD send only the extensions necessary for the client to
ClientHello pair. As with ServerHello, a HelloRetryRequest MUST NOT generate a correct ClientHello pair. As with ServerHello, a
contain any extensions that were not first offered by the client in HelloRetryRequest MUST NOT contain any extensions that were not first
its ClientHello, with the exception of optionally the "cookie" (see offered by the client in its ClientHello, with the exception of
Section 4.2.2) extension. optionally the "cookie" (see Section 4.2.2) extension.
Upon receipt of a HelloRetryRequest, the client MUST verify that the Upon receipt of a HelloRetryRequest, the client MUST verify that the
extensions block is not empty and otherwise MUST abort the handshake extensions block is not empty and otherwise MUST abort the handshake
with a "decode_error" alert. Clients MUST abort the handshake with with a "decode_error" alert. Clients MUST abort the handshake with
an "illegal_parameter" alert if the HelloRetryRequest would not an "illegal_parameter" alert if the HelloRetryRequest would not
result in any change in the ClientHello. If a client receives a result in any change in the ClientHello. If a client receives a
second HelloRetryRequest in the same connection (i.e., where the second HelloRetryRequest in the same connection (i.e., where the
ClientHello was itself in response to a HelloRetryRequest), it MUST ClientHello was itself in response to a HelloRetryRequest), it MUST
abort the handshake with an "unexpected_message" alert. abort the handshake with an "unexpected_message" alert.
Otherwise, the client MUST process all extensions in the Otherwise, the client MUST process all extensions in the
HelloRetryRequest and send a second updated ClientHello. The HelloRetryRequest and send a second updated ClientHello. The
HelloRetryRequest extensions defined in this specification are: HelloRetryRequest extensions defined in this specification are:
- cookie (see Section 4.2.2) - cookie (see Section 4.2.2)
- key_share (see Section 4.2.5) - key_share (see Section 4.2.5)
In addition, in its updated ClientHello, the client SHOULD NOT offer
any pre-shared keys associated with a hash other than that of the
selected cipher suite. This allows the client to avoid having to
compute partial hash transcripts for multiple hashes in the second
ClientHello. A client which receives a cipher suite that was not
offered MUST abort the handshake. Servers MUST ensure that they
negotiate the same cipher suite when receiving a conformant updated
ClientHello (if the server selects the cipher suite as the first step
in the negotiation, then this will happen automatically). Upon
receiving the ServerHello, clients MUST check that the cipher suite
supplied in the ServerHello is the same as that in the
HelloRetryRequest and otherwise abort the handshake with an
"illegal_parameter" alert.
4.2. Extensions 4.2. Extensions
A number of TLS messages contain tag-length-value encoded extensions A number of TLS messages contain tag-length-value encoded extensions
structures. structures.
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), supported_versions(43),
cookie(44), cookie(44),
psk_key_exchange_modes(45), psk_key_exchange_modes(45),
ticket_early_data_info(46), certificate_authorities(47),
oid_filters(48),
(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.
The list of extension types is maintained by IANA as described in The list of extension types is maintained by IANA as described in
Section 10. Section 10.
The client sends its extensions in the ClientHello. The server MAY Extensions are generally structured in a request/response fashion,
send extensions in the ServerHello, EncryptedExtensions, Certificate, though some extensions are just indications with no corresponding
and HelloRetryRequest messages. The NewSessionTicket also allows the response. The client sends its extension requests in the ClientHello
server to send extensions to the client though these are not directly message and the server sends its extension responses in the
associated with the extensions in the ClientHello. The table in ServerHello, EncryptedExtensions and HelloRetryRequest messages. The
Section 10 indicates where a given extension may appear. If the server sends extension requests in the CertificateRequest message
client receives an extension which is not specified for a given which a client MAY respond to with a Certificate message. The server
message it MUST abort the handshake with an "illegal_parameter" MAY also send unsolicited extensions in the NewSessionTicket, though
alert. the client does not respond directly to these.
The server MUST NOT send any extensions which did not appear in the Implementations MUST NOT send extension responses if the remote
corresponding ClientHello, with the exception of the NewSessionTicket endpoint did not send the corresponding extension requests, with the
message and the "cookie" extension in the HelloRetryRequest message. exception of the "cookie" extension in HelloRetryRequest. Upon
Upon receiving an unexpected extension, it MUST abort the handshake receiving such an extension, an endpoint MUST abort the handshake
with an "unsupported_extension" alert. Server-oriented extensions with an "unsupported_extension" alert.
are supported by having the client send an extension with zero-length
extension_data indicating support for that extension type. The table below indicates the messages where a given extension may
appear, using the following notation: CH (ClientHello), SH
(ServerHello), EE (EncryptedExtensions), CT (Certificate), CR
(CertificateRequest), NST (NewSessionTicket) and HRR
(HelloRetryRequest). If an implementation receives an extension
which it recognizes and which is not specified for the message in
which it appears it MUST abort the handshake with an
"illegal_parameter" alert.
+--------------------------------------------------+-------------+
| Extension | TLS 1.3 |
+--------------------------------------------------+-------------+
| server_name [RFC6066] | CH, EE |
| | |
| max_fragment_length [RFC6066] | CH, EE |
| | |
| client_certificate_url [RFC6066] | CH, EE |
| | |
| status_request [RFC6066] | CH, CR, CT |
| | |
| user_mapping [RFC4681] | CH, EE |
| | |
| cert_type [RFC6091] | CH, EE |
| | |
| supported_groups [RFC7919] | CH, EE |
| | |
| signature_algorithms [RFC5246] | CH, CR |
| | |
| use_srtp [RFC5764] | CH, EE |
| | |
| heartbeat [RFC6520] | CH, EE |
| | |
| application_layer_protocol_negotiation [RFC7301] | CH, EE |
| | |
| signed_certificate_timestamp [RFC6962] | CH, CR, CT |
| | |
| client_certificate_type [RFC7250] | CH, EE |
| | |
| server_certificate_type [RFC7250] | CH, CT |
| | |
| padding [RFC7685] | CH |
| | |
| key_share [[this document]] | CH, SH, HRR |
| | |
| pre_shared_key [[this document]] | CH, SH |
| | |
| psk_key_exchange_modes [[this document]] | CH |
| | |
| early_data [[this document]] | CH, EE, NST |
| | |
| cookie [[this document]] | CH, HRR |
| | |
| supported_versions [[this document]] | CH |
| | |
| certificate_authorities [[this document]] | CH, CR |
| | |
| oid_filters [[this document]] | CR |
+--------------------------------------------------+-------------+
When multiple extensions of different types are present, the When multiple extensions of different types are present, the
extensions MAY appear in any order, with the exception of extensions MAY appear in any order, with the exception of
"pre_shared_key" Section 4.2.6 which MUST be the last extension in "pre_shared_key" Section 4.2.8 which MUST be the last extension in
the ClientHello. There MUST NOT be more than one extension of the the ClientHello. There MUST NOT be more than one extension of the
same type. same type.
In TLS 1.3, unlike TLS 1.2, extensions are renegotiated with each In TLS 1.3, unlike TLS 1.2, extensions are renegotiated with each
handshake even when in resumption-PSK mode. However, 0-RTT handshake even when in resumption-PSK mode. However, 0-RTT
parameters are those negotiated in the previous handshake; mismatches parameters are those negotiated in the previous handshake; mismatches
may require rejecting 0-RTT (see Section 4.2.8). may require rejecting 0-RTT (see Section 4.2.7).
There are subtle (and not so subtle) interactions that may occur in There are subtle (and not so subtle) interactions that may occur in
this protocol between new features and existing features which may this protocol between new features and existing features which may
result in a significant reduction in overall security. The following result in a significant reduction in overall security. The following
considerations should be taken into account when designing new considerations should be taken into account when designing new
extensions: extensions:
- Some cases where a server does not agree to an extension are error - Some cases where a server does not agree to an extension are error
conditions, and some are simply refusals to support particular conditions, and some are simply refusals to support particular
features. In general, error alerts should be used for the former, features. In general, error alerts should be used for the former,
skipping to change at page 36, line 20 skipping to change at page 38, line 25
The "supported_versions" extension is used by the client to indicate The "supported_versions" extension is used by the client to indicate
which versions of TLS it supports. The extension contains a list of which versions of TLS it supports. The extension contains a list of
supported versions in preference order, with the most preferred supported versions in preference order, with the most preferred
version first. Implementations of this specification MUST send this version first. Implementations of this specification MUST send this
extension containing all versions of TLS which they are prepared to extension containing all versions of TLS which they are prepared to
negotiate (for this specification, that means minimally 0x0304, but negotiate (for this specification, that means minimally 0x0304, but
if previous versions of TLS are supported, they MUST be present as if previous versions of TLS are supported, they MUST be present as
well). well).
Servers which are compliant with this specification MUST use only the If this extension is not present, servers which are compliant with
"supported_versions" extension, if present, to determine client this specification MUST negotiate TLS 1.2 or prior as specified in
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 0x0304 or later. [RFC5246], even if ClientHello.legacy_version is 0x0304 or later.
If this extension is present, servers MUST ignore the
ClientHello.legacy_version value and MUST use only the
"supported_versions" extension to determine client preferences.
Servers MUST only select a version of TLS present in that extension
and MUST ignore any unknown versions. Note that this mechanism makes
it possible to negotiate a version prior to TLS 1.2 if one side
supports a sparse range. Implementations of TLS 1.3 which choose to
support prior versions of TLS SHOULD support TLS 1.2.
The server MUST NOT send the "supported_versions" extension. The The server MUST NOT send the "supported_versions" extension. The
server's selected version is contained in the ServerHello.version server's selected version is contained in the ServerHello.version
field as in previous versions of TLS. field as in previous versions of TLS.
4.2.1.1. Draft Version Indicator 4.2.1.1. Draft Version Indicator
RFC EDITOR: PLEASE REMOVE THIS SECTION RFC EDITOR: PLEASE REMOVE THIS SECTION
While the eventual version indicator for the RFC version of TLS 1.3 While the eventual version indicator for the RFC version of TLS 1.3
will be 0x0304, implementations of draft versions of this will be 0x0304, implementations of draft versions of this
skipping to change at page 37, line 10 skipping to change at page 39, line 23
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-
connection-oriented transports (see [RFC6347] for an example of connection-oriented transports (see [RFC6347] for an example of
this). this).
- Allowing the server to offload state to the client, thus allowing - Allowing the server to offload state to the client, thus allowing
it to send a HelloRetryRequest without storing any state. The it to send a HelloRetryRequest without storing any state. The
server does this by pickling that post-ClientHello hash state into server does this by storing the hash of the ClientHello in the
the cookie (protected with some suitable integrity algorithm). HelloRetryRequest 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.
4.2.3. 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 itself signatures. Clients which desire the server to authenticate itself
via a certificate MUST send this extension. If a server is via a certificate MUST send this extension. If a server is
authenticating via a certificate and the client has not sent a authenticating via a certificate and the client has not sent a
"signature_algorithms" extension then the server MUST abort the "signature_algorithms" extension, then the server MUST abort the
handshake with a "missing_extension" alert (see Section 8.2). handshake with a "missing_extension" alert (see Section 8.2).
The "extension_data" field of this extension in a ClientHello The "extension_data" field of this extension in a ClientHello
contains a SignatureSchemeList value: contains a SignatureSchemeList 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 (0x0804), rsa_pss_sha256(0x0804),
rsa_pss_sha384 (0x0805), rsa_pss_sha384(0x0805),
rsa_pss_sha512 (0x0806), rsa_pss_sha512(0x0806),
/* EdDSA algorithms */ /* EdDSA algorithms */
ed25519 (0x0807), ed25519(0x0807),
ed448 (0x0808), ed448(0x0808),
/* Reserved Code Points */ /* Reserved Code Points */
private_use (0xFE00..0xFFFF), private_use(0xFE00..0xFFFF),
(0xFFFF) (0xFFFF)
} SignatureScheme; } SignatureScheme;
struct { struct {
SignatureScheme supported_signature_algorithms<2..2^16-2>; SignatureScheme supported_signature_algorithms<2..2^16-2>;
} SignatureSchemeList; } SignatureSchemeList;
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.
skipping to change at page 38, line 51 skipping to change at page 40, line 51
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 algorithm 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 4.4.1.2) and are not which appear in certificates (see Section 4.4.2.2) 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 mask generation function 1. The digest used in
function and the digest being signed are both the corresponding the mask generation function and the digest being signed are both
hash algorithm as defined in [SHS]. When used in signed TLS the corresponding hash algorithm as defined in [SHS]. When used
handshake messages, the length of the salt MUST be equal to the in signed TLS handshake messages, the length of the salt MUST be
length of the digest output. This codepoint is defined for use equal to the length of the digest output. This codepoint is also
with TLS 1.2 as well as TLS 1.3. defined for use with TLS 1.2.
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 [RFC8032] or its successors. Note that these
these correspond to the "PureEdDSA" algorithms and not the correspond to the "PureEdDSA" algorithms and not the "prehash"
"prehash" variants. variants.
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 them as the lowest priority (listed after all other algorithms in
SignatureSchemeList). TLS 1.3 servers MUST NOT offer a SHA-1 signed SignatureSchemeList). TLS 1.3 servers MUST NOT offer a SHA-1 signed
certificate unless no valid certificate chain can be produced without certificate unless no valid certificate chain can be produced without
it (see Section 4.4.1.2). it (see Section 4.4.2.2).
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 40, line 16 skipping to change at page 42, line 16
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. In TLS 1.2, using that scheme even when TLS 1.2 is negotiated. In TLS 1.2,
RSASSA-PSS is used with RSA cipher suites. RSASSA-PSS is used with RSA cipher suites.
4.2.3.1. Certificate Authorities
The "certificate_authorities" extension is used to indicate the
certificate authorities which an endpoint supports and which SHOULD
be used by the receiving endpoint to guide certificate selection.
The body of the "certificate_authorities" extension consists of a
CertificateAuthoritiesExtension structure.
opaque DistinguishedName<1..2^16-1>;
struct {
DistinguishedName authorities<3..2^16-1>;
} CertificateAuthoritiesExtension;
authorities A list of the distinguished names [X501] of acceptable
certificate authorities, represented in DER-encoded [X690] format.
These distinguished names specify a desired distinguished name for
trust anchor or subordinate CA; thus, this message can be used to
describe known trust anchors as well as a desired authorization
space.
The client MAY send the "certificate_authorities" extension in the
ClientHello message. The server MAY send it in the
CertificateRequest message.
The "trusted_ca_keys" extension, which serves a similar purpose
[RFC6066], but is more complicated, is not used in TLS 1.3 (although
it may appear in ClientHello messages from clients which are offering
prior versions of TLS).
4.2.4. 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 [RFC7919]. This extension was also used to negotiate [RFC4492] and [RFC7919]. This extension was also used to negotiate
ECDSA curves. Signature algorithms are now negotiated independently ECDSA curves. Signature algorithms are now negotiated independently
(see Section 4.2.3). (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(0x0017), secp384r1(0x0018), secp521r1(0x0019),
x25519 (29), x448 (30), x25519(0x001D), x448(0x001E),
/* Finite Field Groups (DHE) */ /* Finite Field Groups (DHE) */
ffdhe2048 (256), ffdhe3072 (257), ffdhe4096 (258), ffdhe2048(0x0100), ffdhe3072(0x0101), ffdhe4096 (0x0102),
ffdhe6144 (259), ffdhe8192 (260), ffdhe6144(0x0103), ffdhe8192(0x0104),
/* 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<2..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 for the
named curve, defined either in FIPS 186-4 [DSS] or in [RFC7748]. corresponding named curve, defined either in FIPS 186-4 [DSS] or
Values 0xFE00 through 0xFEFF are reserved for private use. in [RFC7748]. Values 0xFE00 through 0xFEFF are reserved for
private use.
Finite Field Groups (DHE) Indicates support of the corresponding Finite Field Groups (DHE) Indicates support of the corresponding
finite field group, defined in [RFC7919]. Values 0x01FC through finite field group, defined in [RFC7919]. 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
skipping to change at page 41, line 45 skipping to change at page 44, line 29
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 4.2.5.1; 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 4.2.5.2. 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.
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 (Handshake.msg_type) { select (Handshake.msg_type) {
case client_hello: case client_hello:
KeyShareEntry client_shares<0..2^16-1>; KeyShareEntry client_shares<0..2^16-1>;
case hello_retry_request: case hello_retry_request:
NamedGroup selected_group; NamedGroup selected_group;
case server_hello: 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. Each KeyShareEntry
here SHOULD match that of the ordering of offered support in the value MUST correspond to a group offered in the "supported_groups"
"supported_groups" extension. extension and MUST appear in the same order. However, the values
MAY be a non-contiguous subset of the "supported_groups" extension
and MAY omit the most preferred groups.
selected_group The mutually supported group the server intends to selected_group The mutually supported group the server intends to
negotiate and is requesting a retried ClientHello/KeyShare for. 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
skipping to change at page 42, line 50 skipping to change at page 45, line 33
Upon receipt of this extension in a HelloRetryRequest, the client Upon receipt of this extension in a HelloRetryRequest, the client
MUST verify that (1) the selected_group field corresponds to a group MUST verify that (1) the selected_group field corresponds to a group
which was provided in the "supported_groups" extension in the which was provided in the "supported_groups" extension in the
original ClientHello; and (2) the selected_group field does not original ClientHello; and (2) the selected_group field does not
correspond to a group which was provided in the "key_share" extension correspond to a group which was provided in the "key_share" extension
in the original ClientHello. If either of these checks fails, then in the original ClientHello. If either of these checks fails, then
the client MUST abort the handshake with an "illegal_parameter" the client MUST abort the handshake with an "illegal_parameter"
alert. Otherwise, when sending the new ClientHello, the client MUST alert. Otherwise, when sending the new ClientHello, the client MUST
replace the original "key_share" extension with one containing only a replace the original "key_share" extension with one containing only a
new KeyShareEntry for the group indicated in the selected_group new KeyShareEntry for the group indicated in the selected_group field
field. of the triggering HelloRetryRequest.
If using (EC)DHE key establishment, servers offer exactly one If using (EC)DHE key establishment, servers offer exactly one
KeyShareEntry in the ServerHello. This value MUST correspond to the KeyShareEntry in the ServerHello. This value MUST correspond to the
KeyShareEntry value offered by the client that the server has KeyShareEntry value offered by the client that the server has
selected for the negotiated key exchange. Servers MUST NOT send a selected for the negotiated key exchange. Servers MUST NOT send a
KeyShareEntry for any group not indicated in the "supported_groups" KeyShareEntry for any group not indicated in the "supported_groups"
extension. If a HelloRetryRequest was received, the client MUST extension and MUST NOT send a KeyShareEntry when using the "psk_ke"
verify that the selected NamedGroup matches that supplied in the PskKeyExchangeMode. If a HelloRetryRequest was received by the
selected_group field and MUST abort the handshake with an client, the client MUST verify that the selected NamedGroup in the
"illegal_parameter" alert if it does not. ServerHello is the same as that in the HelloRetryRequest. If this
check fails, the client MUST abort the handshake with an
"illegal_parameter" alert.
4.2.5.1. 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) for the specified group (see [RFC7919] public value (Y = g^X mod p) for the specified group (see [RFC7919]
for group definitions) encoded as a big-endian integer, padded with for group definitions) encoded as a big-endian integer and padded
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 MUST validate each other's public key Y by ensuring that 1 < Y
Y < p-1. This check ensures that the remote peer is properly behaved < 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.
4.2.5.2. 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).
Peers MUST validate each other's public value Y by ensuring that the
point is a valid point on the elliptic curve.
For x25519 and x448, the contents are the byte string inputs and For the curves secp256r1, secp384r1 and secp521r1, the appropriate
outputs of the corresponding functions defined in [RFC7748], 32 bytes validation procedures are defined in Section 4.3.7 of [X962] and
for x25519 and 56 bytes for x448. alternatively in Section 5.6.2.6 of [KEYAGREEMENT]. This process
consists of three steps: (1) verify that Y is not the point at
infinity (O), (2) verify that for Y = (x, y) both integers are in the
correct interval, (3) ensure that (x, y) is a correct solution to the
elliptic curve equation. For these curves, implementers do not need
to verify membership in the correct subgroup.
For X25519 and X448, the contents of the public value are the byte
string inputs and outputs of the corresponding functions defined in
[RFC7748], 32 bytes for X25519 and 56 bytes for X448.
Note: Versions of TLS prior to 1.3 permitted point format Note: Versions of TLS prior to 1.3 permitted point format
negotiation; TLS 1.3 removes this feature in favor of a single point negotiation; TLS 1.3 removes this feature in favor of a single point
format for each curve. format for each curve.
4.2.6. Pre-Shared Key Extension 4.2.6. Pre-Shared Key Exchange Modes
In order to use PSKs, clients MUST also send a
"psk_key_exchange_modes" extension. The semantics of this extension
are that the client only supports the use of PSKs with these modes,
which restricts both the use of PSKs offered in this ClientHello and
those which the server might supply via NewSessionTicket.
A client MUST provide a "psk_key_exchange_modes" extension if it
offers a "pre_shared_key" extension. If clients offer
"pre_shared_key" without a "psk_key_exchange_modes" extension,
servers MUST abort the handshake. Servers MUST NOT select a key
exchange mode that is not listed by the client. This extension also
restricts the modes for use with PSK resumption; servers SHOULD NOT
send NewSessionTicket with tickets that are not compatible with the
advertised modes; however, if a server does so, the impact will just
be that the client's attempts at resumption fail.
The server MUST NOT send a "psk_key_exchange_modes" extension.
enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeMode;
struct {
PskKeyExchangeMode ke_modes<1..255>;
} PskKeyExchangeModes;
psk_ke PSK-only key establishment. In this mode, the server MUST
NOT supply a "key_share" value.
psk_dhe_ke PSK with (EC)DHE key establishment. In this mode, the
client and servers MUST supply "key_share" values as described in
Section 4.2.5.
4.2.7. Early Data Indication
When a PSK is used, the client can send application data in 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" extension.
The "extension_data" field of this extension contains an
"EarlyDataIndication" value.
struct {} Empty;
struct {
select (Handshake.msg_type) {
case new_session_ticket: uint32 max_early_data_size;
case client_hello: Empty;
case encrypted_extensions: Empty;
};
} EarlyDataIndication;
See Appendix B.3.4 for the use of the max_early_data_size field.
For PSKs provisioned via NewSessionTicket, a server MUST validate
that the ticket age for the selected PSK identity (computed by
subtracting ticket_age_add from PskIdentity.obfuscated_ticket_age
modulo 2^32) is within a small tolerance of the time since the ticket
was issued (see Section 4.2.8.3). If it is not, the server SHOULD
proceed with the handshake but reject 0-RTT, and SHOULD NOT take any
other action that assumes that this ClientHello is fresh.
The parameters for the 0-RTT data (symmetric cipher suite, ALPN
protocol, etc.) are the same as those which were negotiated in the
connection 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" extension.
0-RTT messages sent in the first flight have the same (encrypted)
content types as their corresponding messages sent in other flights
(handshake, application_data, and alert respectively) but are
protected under different keys. After receiving the server's
Finished message, if the server has accepted early data, an
EndOfEarlyData message will be sent to indicate the key change. This
message will be encrypted with the 0-RTT traffic keys.
A server which receives an "early_data" extension MUST behave in one
of three ways:
- Ignore the extension and return a regular 1-RTT response. The
server then ignores early data using trial decryption until it is
able to receive the client's second flight and complete an
ordinary 1-RTT handshake.
- 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. The server
then ignores early data by skipping all records with external
content type of "application_data" (indicating that they are
encrypted).
- Return its own extension in EncryptedExtensions, indicating that
it intends to process the early data. It is not possible for the
server to accept only a subset of the early data messages.
In order to accept early data, the server MUST have accepted a PSK
cipher suite and selected the first key offered in the client's
"pre_shared_key" extension. In addition, it MUST verify that the
following values are consistent with those negotiated in the
connection during which the ticket was established.
- The TLS version number and cipher suite.
- The selected ALPN [RFC7301] protocol, if any.
Future extensions MUST define their interaction with 0-RTT.
If any of these checks fail, the server MUST NOT respond with the
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
the server rejects it, the server will generally not have the 0-RTT
record protection keys and must instead trial decrypt each record
with the 1-RTT handshake keys until it finds one that decrypts
properly, and then pick up the handshake from that point.
If the server chooses to accept the "early_data" extension, then it
MUST comply with the same error handling requirements specified for
all records when processing early data records. Specifically, if the
server fails to decrypt any 0-RTT record following an accepted
"early_data" extension it MUST terminate the connection with a
"bad_record_mac" alert as per Section 5.2.
If the server rejects the "early_data" extension, the client
application MAY opt to retransmit early data once the handshake has
been completed. A TLS implementation SHOULD NOT automatically re-
send early data; applications are in a better position to decide when
re-transmission is appropriate. Automatic re-transmission of early
data could result in assumptions about the status of the connection
being incorrect. In particular, a TLS implementation MUST NOT
automatically re-send early data unless the negotiated connection
selects the same ALPN protocol. An application might need to
construct different messages if a different protocol is selected.
Similarly, if early data assumes anything about the connection state,
it might be sent in error after the handshake completes.
4.2.8. 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. with PSK key establishment.
The "extension_data" field of this extension contains a The "extension_data" field of this extension contains a
"PreSharedKeyExtension" value: "PreSharedKeyExtension" value:
struct { struct {
opaque identity<0..2^16-1>; opaque identity<1..2^16-1>;
uint32 obfuscated_ticket_age; uint32 obfuscated_ticket_age;
} PskIdentity; } PskIdentity;
opaque PskBinderEntry<32..255>; opaque PskBinderEntry<32..255>;
struct { struct {
select (Handshake.msg_type) { select (Handshake.msg_type) {
case client_hello: case client_hello:
PskIdentity identities<6..2^16-1>; PskIdentity identities<7..2^16-1>;
PskBinderEntry binders<33..2^16-1>; PskBinderEntry binders<33..2^16-1>;
case server_hello: case server_hello:
uint16 selected_identity; uint16 selected_identity;
}; };
} PreSharedKeyExtension; } PreSharedKeyExtension;
identities A list of the identities (labels for keys) that the identity A label for a key. For instance, a ticket defined in
client is willing to negotiate with the server. If sent alongside Appendix B.3.4, or a label for a pre-shared key established
the "early_data" extension (see Section 4.2.8), the first identity externally.
is the one used for 0-RTT data.
obfuscated_ticket_age For each ticket, the time since the client obfuscated_ticket_age For each ticket, the time since the client
learned about the server configuration that it is using, in learned about the server configuration that it is using, in
milliseconds. This value is added modulo 2^32 to with the milliseconds. This value is added modulo 2^32 to the
"ticket_age_add" value that was included with the ticket, see "ticket_age_add" value that was included with the ticket, see
Section 4.5.1. This addition prevents passive observers from Section 4.6.1. This addition prevents passive observers from
correlating sessions unless tickets are reused. Note: because correlating connections unless tickets are reused. Note: because
ticket lifetimes are restricted to a week, 32 bits is enough to ticket lifetimes are restricted to a week, 32 bits is enough to
represent any plausible age, even in milliseconds. External represent any plausible age, even in milliseconds. For identities
tickets SHOULD use an obfuscated_ticket_age of 0; servers MUST established externally an obfuscated_ticket_age of 0 SHOULD be
ignore this value for external tickets. used, and servers MUST ignore the value.
identities A list of the identities that the client is willing to
negotiate with the server. If sent alongside the "early_data"
extension (see Section 4.2.7), the first identity is the one used
for 0-RTT data.
binders A series of HMAC values, one for each PSK offered in the binders A series of HMAC values, one for each PSK offered in the
"pre_shared_keys" extension and in the same order, computed as "pre_shared_keys" extension and in the same order, computed as
described below. described below.
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 identities in the client's list. (0-based) index into the identities in the client's list.
Each PSK is associated with a single Hash algorithm. For PSKs Each PSK is associated with a single Hash algorithm. For PSKs
established via the ticket mechanism (Section 4.5.1), this is the established via the ticket mechanism (Section 4.6.1), this is the
Hash used for the KDF. For externally established PSKs, the Hash Hash used for the KDF. For externally established PSKs, the Hash
algorithm MUST be set when the PSK is established. algorithm MUST be set when the PSK is established. The server must
ensure that it selects a compatible PSK (if any) and cipher suites.
Implementor's note: the most straightforward way to implement the
PSK/cipher suite matching requirements is to negotiate the cipher
suite first and then exclude any incompatible PSKs. Any unknown PSKs
(e.g., they are not in the PSK database or are encrypted with an
unknown key) SHOULD simply be ignored. If no acceptable PSKs are
found, the server SHOULD perform a non-PSK handshake if possible.
Prior to accepting PSK key establishment, the server MUST validate Prior to accepting PSK key establishment, the server MUST validate
the corresponding binder value (see Section 4.2.6.1 below). If this the corresponding binder value (see Section 4.2.8.1 below). If this
value is not present or does not validate, the server MUST abort the value is not present or does not validate, the server MUST abort the
handshake. Servers SHOULD NOT attempt to validate multiple binders; handshake. Servers SHOULD NOT attempt to validate multiple binders;
rather they SHOULD select a single PSK and validate solely the binder rather they SHOULD select a single PSK and validate solely the binder
that corresponds to that PSK. In order to accept PSK key that corresponds to that PSK. In order to accept PSK key
establishment, the server sends a "pre_shared_key" extension establishment, the server sends a "pre_shared_key" extension
indicating the selected identity. indicating the selected identity.
Clients MUST verify that the server's selected_identity is within the Clients MUST verify that the server's selected_identity is within the
range supplied by the client, that the server selected the cipher range supplied by the client, that the server selected a cipher suite
suite associated with the PSK, and that the "key_share", and containing a Hash associated with the PSK and that a server
"signature_algorithms" extensions are consistent with the indicated "key_share" extension is present if required by the ClientHello
ke_modes and auth_modes values. If these values are not consistent, "psk_key_exchange_modes". If these values are not consistent the
the client MUST abort the handshake with an "illegal_parameter" client MUST abort the handshake with an "illegal_parameter" alert.
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's selected_identity is 0. If any other value verify that the server's selected_identity is 0. If any other value
is returned, the client MUST abort the handshake with an is returned, the client MUST abort the handshake with an
"illegal_parameter" alert. "illegal_parameter" alert.
This extension MUST be the last extension in the ClientHello (this This extension MUST be the last extension in the ClientHello (this
facilitates implementation as described below). Servers MUST check facilitates implementation as described below). Servers MUST check
that it is the last extension and otherwise fail the handshake with that it is the last extension and otherwise fail the handshake with
an "illegal_parameter" alert. an "illegal_parameter" alert.
4.2.6.1. PSK Binder 4.2.8.1. PSK Binder
The PSK binder value forms a binding between a PSK and the current The PSK binder value forms a binding between a PSK and the current
handshake, as well as between the session where the PSK was handshake, as well as between the handshake in which the PSK was
established (if via a NewSessionTicket message) and the session where generated (if via a NewSessionTicket message) and the handshake where
it was used. Each entry in the binders list is computed as an HMAC it was used. Each entry in the binders list is computed as an HMAC
over the portion of the ClientHello up to and including the over a transcript hash (see Section 4.4.1) containing a partial
PreSharedKeyExtension.identities field. That is, it includes all of ClientHello up to and including the PreSharedKeyExtension.identities
the ClientHello but not the binder list itself. The length fields field. That is, it includes all of the ClientHello but not the
for the message (including the overall length, the length of the binders list itself. The length fields for the message (including
extensions block, and the length of the "pre_shared_key" extension) the overall length, the length of the extensions block, and the
are all set as if the binder were present. length of the "pre_shared_key" extension) are all set as if binders
of the correct lengths were present.
The binding_value is computed in the same way as the Finished message The binding_value is computed in the same way as the Finished message
(Section 4.4.3) but with the BaseKey being the binder_key (see (Section 4.4.4) but with the BaseKey being the binder_key derived via
Section 7.1). the key schedule from the corresponding PSK which is being offered
(see Section 7.1).
If the handshake includes a HelloRetryRequest, the initial If the handshake includes a HelloRetryRequest, the initial
ClientHello and HelloRetryRequest are included in the transcript ClientHello and HelloRetryRequest are included in the transcript
along with the new ClientHello. For instance, if the client sends along with the new ClientHello. For instance, if the client sends
ClientHello1, its binder will be computed over: ClientHello1, its binder will be computed over:
ClientHello1[truncated] Transcript-Hash(ClientHello1[truncated])
If the server responds with HelloRetryRequest, and the client then If the server responds with HelloRetryRequest, and the client then
sends ClientHello2, its binder will be computed over: sends ClientHello2, its binder will be computed over:
ClientHello1 + HelloRetryRequest + ClientHello2[truncated] Transcript-Hash(ClientHello1,
HelloRetryRequest,
ClientHello2[truncated])
The full ClientHello is included in all other handshake hash The full ClientHello is included in all other handshake hash
computations. computations. Note that in the first flight, ClientHello1[truncated]
is hashed directly, but in the second flight, it is hashed and then
4.2.7. Pre-Shared Key Exchange Modes reinjected as a "handshake_hash" message, as described in
Section 4.4.1.
In order to use PSKs, clients MUST also send a
"psk_key_exchange_modes" extension. The semantics of this extension
are that the client only supports the use of PSKs with these modes,
which restricts both the use of PSKs offered in this ClientHello and
those which the server might supply via NewSessionTicket.
A clients MUST provide a "psk_key_exchange_modes" extension if it
offers a "pre_shared_key" extension. If clients offer
"pre_shared_key" without a "psk_key_exchange_modes" extension,
servers MUST abort the handshake. Servers MUST NOT select a key
exchange mode that is not listed by the client. This extension also
restricts the modes for use with PSK resumption; servers SHOULD NOT
send NewSessionTicket with tickets that are not compatible with the
advertised modes; however if it does so, the impact will just be that
the client's attempts at resumption fail.
The server MUST NOT send a "psk_key_exchange_modes" extension.
enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeMode;
struct {
PskKeyExchangeMode ke_modes<1..255>;
} PskKeyExchangeModes;
psk_ke PSK-only key establishment. In this mode, the server MUST
NOT supply a "key_share" value.
psk_dhe_ke PSK key establishment with (EC)DHE key establishment. In
this mode, the client and servers MUST supply "key_share" values
as described in Section 4.2.5.
4.2.8. Early Data Indication
When a PSK is used, the client can send application data in 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" extension.
The "extension_data" field of this extension contains an
"EarlyDataIndication" value:
struct {
} EarlyDataIndication;
For PSKs provisioned via NewSessionTicket, a server MUST validate
that the ticket age for the selected PSK identity (computed by un-
masking PskIdentity.obfuscated_ticket_age) is within a small
tolerance of the time since the ticket was issued (see
Section 4.2.8.2). If it is not, the server SHOULD proceed with the
handshake but reject 0-RTT, and SHOULD NOT take any other action that
assumes that this ClientHello is fresh.
The parameters for the 0-RTT data (symmetric cipher suite, ALPN
protocol, etc.) are the same as those which were negotiated in the
connection 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" extension.
0-RTT messages sent in the first flight have the same content types
as their corresponding messages sent in other flights (handshake,
application_data, and alert respectively) but are protected under
different keys. After all the 0-RTT application data messages (if
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
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
of two ways:
- Ignore the extension and return no response. This indicates that
the server has ignored any early data and an ordinary 1-RTT
handshake is required.
- Return its own extension, indicating that it intends to process
the early data. It is not possible for the server to accept only
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 MUST have accepted a PSK
cipher suite and selected the first key offered in the client's
"pre_shared_key" extension. In addition, it MUST verify that the
following values are consistent with those negotiated in the
connection during which the ticket was established.
- The TLS version number and cipher suite.
- The selected ALPN [RFC7301] protocol, if any.
Future extensions MUST define their interaction with 0-RTT.
If any of these checks fail, the server MUST NOT respond with the
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
the server rejects it, it will generally not have the 0-RTT record
protection keys and must instead trial decrypt each record with the
1-RTT handshake keys until it finds one that decrypts properly, and
then pick up the handshake from that point.
If the server chooses to accept the "early_data" extension, then it
MUST comply with the same error handling requirements specified for
all records when processing early data records. Specifically, if the
server fails to decrypt any 0-RTT record following an accepted
"early_data" extension it MUST terminate the connection with a
"bad_record_mac" alert as per Section 5.2.
If the server rejects the "early_data" extension, the client
application MAY opt to retransmit the data once the handshake has
been completed. TLS stacks SHOULD not do this automatically and
client applications MUST take care that the negotiated parameters are
consistent with those it expected. For example, if the selected ALPN
protocol has changed, it is likely unsafe to retransmit the original
application layer data.
4.2.8.1. Processing Order 4.2.8.2. 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 EndOfEarlyData message. In
In order to avoid deadlock, when accepting "early_data", servers MUST order to avoid deadlocks, when accepting "early_data", servers MUST
process the client's ClientHello and then immediately send the process the client's ClientHello 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 EndOfEarlyData
alert. message.
4.2.8.2. Replay Properties 4.2.8.3. 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 The "obfuscated_ticket_age" parameter in the client's
"pre_shared_key" extension SHOULD be used by servers to limit the "pre_shared_key" extension SHOULD be used by servers to limit the
time over which the first flight might be replayed. A server can time over which the first flight might be replayed. A server can
store the time at which it sends a session ticket to the client, or store the time at which it sends a ticket to the client, or encode
encode the time in the ticket. Then, each time it receives an the time in the ticket. Then, each time it receives an
"pre_shared_key" extension, it can subtract the base value and check "pre_shared_key" extension, it can subtract the base value and check
to see if the value used by the client matches its expectations. to see if the value used by the client matches its expectations.
The ticket age (the value with "ticket_age_add" subtracted) provided The ticket age (the value with "ticket_age_add" subtracted) provided
by the client will be shorter than the actual time elapsed on the by the client will be shorter than the actual time elapsed on the
server by a single round trip time. This difference is comprised of server by a single round trip time. This difference is comprised of
the delay in sending the NewSessionTicket message to the client, plus the delay in sending the NewSessionTicket message to the client, plus
the time taken to send the ClientHello to the server. For this the time taken to send the ClientHello to the server. For this
reason, a server SHOULD measure the round trip time prior to sending reason, a server SHOULD measure the round trip time prior to sending
the NewSessionTicket message and account for that in the value it the NewSessionTicket message and account for that in the value it
skipping to change at page 49, line 42 skipping to change at page 53, line 39
- The time that the server generated the session ticket and the - The time that the server generated the session ticket and the
estimated round trip time can be added together to form a baseline estimated round trip time can be added together to form a baseline
time. time.
- The "ticket_age_add" parameter from the NewSessionTicket is needed - The "ticket_age_add" parameter from the NewSessionTicket is needed
to recover the ticket age from the "obfuscated_ticket_age" to recover the ticket age from the "obfuscated_ticket_age"
parameter. parameter.
There are several potential sources of error that make an exact There are several potential sources of error that make an exact
measurement of time difficult. Variations in client and server measurement of time difficult. Variations in client and server clock
clocks are likely to be minimal, outside of gross time corrections. rates are likely to be minimal, though potentially with gross time
Network propagation delays are most likely causes of a mismatch in corrections. Network propagation delays are most likely causes of a
legitimate values for elapsed time. Both the NewSessionTicket and mismatch in legitimate values for elapsed time. Both the
ClientHello messages might be retransmitted and therefore delayed, NewSessionTicket and ClientHello messages might be retransmitted and
which might be hidden by TCP. therefore delayed, which might be hidden by TCP.
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.
4.3. Server Parameters 4.3. Server Parameters
The next two messages from the server, EncryptedExtensions and The next two messages from the server, EncryptedExtensions and
CertificateRequest, contain encrypted information from the server CertificateRequest, contain information from the server that
that determines the rest of the handshake. determines the rest of the handshake. These messages are encrypted
with keys derived from the server_handshake_traffic_secret.
4.3.1. Encrypted Extensions 4.3.1. Encrypted Extensions
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 first message immediately after the ServerHello message. This is the first
message that is encrypted under keys derived from message that is encrypted under keys derived from the
handshake_traffic_secret. server_handshake_traffic_secret.
The EncryptedExtensions message contains extensions which should be The EncryptedExtensions message contains extensions which should be
protected, i.e., any which are not needed to establish the protected, i.e., any which are not needed to establish the
cryptographic context, but which are not associated with individual cryptographic context, but which are not associated with individual
certificates. The client MUST check EncryptedExtensions for the certificates. The client MUST check EncryptedExtensions for the
presence of any forbidden extensions and if any are found MUST abort presence of any forbidden extensions and if any are found MUST abort
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. For more information, see the
table in Section 4.2.
4.3.2. Certificate Request 4.3.2. Certificate Request
A server which is authenticating with a certificate can optionally A server which is authenticating with a certificate MAY optionally
request a certificate from the client. This message, if sent, will request a certificate from the client. This message, if sent, MUST
follow EncryptedExtensions. follow EncryptedExtensions.
Structure of this message: Structure of this message:
opaque DistinguishedName<1..2^16-1>;
struct {
opaque certificate_extension_oid<1..2^8-1>;
opaque certificate_extension_values<0..2^16-1>;
} CertificateExtension;
struct { struct {
opaque certificate_request_context<0..2^8-1>; opaque certificate_request_context<0..2^8-1>;
SignatureScheme Extension extensions<2..2^16-1>;
supported_signature_algorithms<2..2^16-2>;
DistinguishedName certificate_authorities<0..2^16-1>;
CertificateExtension certificate_extensions<0..2^16-1>;
} CertificateRequest; } CertificateRequest;
certificate_request_context An opaque string which identifies the certificate_request_context An opaque string which identifies the
certificate request and which will be echoed in the client's certificate request and which will be echoed in the client's
Certificate message. The certificate_request_context MUST be Certificate message. The certificate_request_context MUST be
unique within the scope of this connection (thus preventing replay unique within the scope of this connection (thus preventing replay
of client CertificateVerify messages). This field SHALL be zero of client CertificateVerify messages). This field SHALL be zero
length unless used for the post-handshake authentication exchanges length unless used for the post-handshake authentication exchanges
described in Section 4.5.2. described in Section 4.6.2.
supported_signature_algorithms A list of the signature algorithms extensions An optional set of extensions describing the parameters
that the server is able to verify, listed in descending order of of the certificate being requested. The "signature_algorithms"
preference. Any certificates provided by the client MUST be extension MUST be specified. Clients MUST ignore unrecognized
signed using a signature algorithm found in extensions.
supported_signature_algorithms.
certificate_authorities A list of the distinguished names [X501] of In prior versions of TLS, the CertificateRequest message carried a
acceptable certificate_authorities, represented in DER-encoded list of signature algorithms and certificate authorities which the
[X690] format. These distinguished names may specify a desired server would accept. In TLS 1.3 the former is expressed by sending
distinguished name for a root CA or for a subordinate CA; thus, the "signature_algorithms" extension. The latter is expressed by
this message can be used to describe known roots as well as a sending the "certificate_authorities" extension (see
desired authorization space. If the certificate_authorities list Section 4.2.3.1).
is empty, then the client MAY send any certificate that meets the
rest of the selection criteria in the CertificateRequest, unless
there is some external arrangement to the contrary.
certificate_extensions A list of certificate extension OIDs Servers which are authenticating with a PSK MUST NOT send the
[RFC5280] with their allowed values, represented in DER-encoded CertificateRequest message.
[X690] format. Some certificate extension OIDs allow multiple
values (e.g. Extended Key Usage). If the server has included a 4.3.2.1. OID Filters
non-empty certificate_extensions list, the client certificate MUST
contain all of the specified extension OIDs that the client The "oid_filters" extension allows servers to provide a set of OID/
recognizes. For each extension OID recognized by the client, all value pairs which it would like the client's certificate to match.
of the specified values MUST be present in the client certificate This extension MUST only be sent in the CertificateRequest message.
(but the certificate MAY have other values as well). However, the
client MUST ignore and skip any unrecognized certificate extension struct {
OIDs. If the client has ignored some of the required certificate opaque certificate_extension_oid<1..2^8-1>;
extension OIDs, and supplied a certificate that does not satisfy opaque certificate_extension_values<0..2^16-1>;
the request, the server MAY at its discretion either continue the } OIDFilter;
session without client authentication, or abort the handshake with
an "unsupported_certificate" alert. PKIX RFCs define a variety of struct {
OIDFilter filters<0..2^16-1>;
} OIDFilterExtension;
filters A list of certificate extension OIDs [RFC5280] with their
allowed values, represented in DER-encoded [X690] format. Some
certificate extension OIDs allow multiple values (e.g., Extended
Key Usage). If the server has included a non-empty
certificate_extensions list, the client certificate included in
the response MUST contain all of the specified extension OIDs that
the client recognizes. For each extension OID recognized by the
client, all of the specified values MUST be present in the client
certificate (but the certificate MAY have other values as well).
However, the client MUST ignore and skip any unrecognized
certificate extension OIDs. If the client ignored some of the
required certificate extension OIDs and supplied a certificate
that does not satisfy the request, the server MAY at its
discretion either continue the connection without client
authentication, or abort the handshake with an
"unsupported_certificate" alert. PKIX RFCs define a variety of
certificate extension OIDs and their corresponding value types. certificate extension OIDs and their corresponding value types.
Depending on the type, matching certificate extension values are Depending on the type, matching certificate extension values are
not necessarily bitwise-equal. It is expected that TLS not necessarily bitwise-equal. It is expected that TLS
implementations will rely on their PKI libraries to perform implementations will rely on their PKI libraries to perform
certificate selection using certificate extension OIDs. This certificate selection using certificate extension OIDs. 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
skipping to change at page 52, line 31 skipping to change at page 56, line 29
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.
Servers which are authenticating with a PSK MUST NOT send the
CertificateRequest message.
4.4. 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 generally uses a common set of
authentication, key confirmation, and handshake integrity: messages for authentication, key confirmation, and handshake
Certificate, CertificateVerify, and Finished. These messages are integrity: Certificate, CertificateVerify, and Finished. (The
always sent as the last messages in their handshake flight. The PreSharedKey binders also perform key confirmation, in a similar
Certificate and CertificateVerify messages are only sent under fashion.) These three messages are always sent as the last messages
certain circumstances, as defined below. The Finished message is in their handshake flight. The Certificate and CertificateVerify
always sent as part of the Authentication block. messages are only sent under certain circumstances, as defined below.
The Finished message is always sent as part of the Authentication
block. These messages are encrypted under keys derived from
[sender]_handshake_traffic_secret.
The computations for the Authentication messages all uniformly take The computations for the Authentication messages all uniformly take
the following inputs: the following inputs:
- The certificate and signing key to be used. - The certificate and signing key to be used.
- A Handshake Context based on the hash of the handshake messages - A Handshake Context consisting of the set of messages to be
included in the transcript hash.
- 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 Transcript-
+ Certificate) Hash(Handshake Context, Certificate)
Finished A MAC over the value Hash(Handshake Context + Certificate +
CertificateVerify) using a MAC key derived from the base key.
Because the CertificateVerify signs the Handshake Context + Finished A MAC over the value Transcript-Hash(Handshake Context,
Certificate and the Finished MACs the Handshake Context + Certificate Certificate, CertificateVerify) using a MAC key derived from the
+ CertificateVerify, this is mostly equivalent to keeping a running base key.
hash of the handshake messages (exactly so in the pure 1-RTT cases).
Note, however, that subsequent post-handshake authentications do not
include each other, just the messages through the end of the main
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 |
+------------+-----------------------------+------------------------+ +------------+-----------------------------+------------------------+
| Server | ClientHello ... later of En | server_handshake_traff | | Server | ClientHello ... later of En | server_handshake_traff |
| | cryptedExtensions/Certifica | ic_secret | | | cryptedExtensions/Certifica | ic_secret |
| | teRequest | | | | teRequest | |
| | | | | | | |
| Client | ClientHello ... | client_handshake_traff | | Client | ClientHello ... | client_handshake_traff |
| | ServerFinished | ic_secret | | | ServerFinished | ic_secret |
| | | | | | | |
| Post- | ClientHello ... | client_traffic_secret_ | | Post- | ClientHello ... | client_traffic_secret_ |
| Handshake | ClientFinished + | N | | Handshake | ClientFinished + | N |
| | CertificateRequest | | | | CertificateRequest | |
+------------+-----------------------------+------------------------+ +------------+-----------------------------+------------------------+
In all cases, the handshake context is formed by concatenating the 4.4.1. The Transcript Hash
indicated handshake messages, including the handshake message type
and length fields.
4.4.1. Certificate Many of the cryptographic computations in TLS make use of a
transcript hash. This value is computed by hashing the concatenation
of each included handshake message, including the handshake message
header carrying the handshake message type and length fields, but not
including record layer headers. I.e.,
Transcript-Hash(M1, M2, ... MN) = Hash(M1 || M2 ... MN)
As an exception to this general rule, when the server responds to a
ClientHello with a HelloRetryRequest, the value of ClientHello1 is
replaced with a special synthetic handshake message of handshake type
"message_hash" containing Hash(ClientHello1). I.e.,
Transcript-Hash(ClientHello1, HelloRetryRequest, ... MN) =
Hash(message_hash || // Handshake Type
00 00 Hash.length || // Handshake message length
Hash(ClientHello1) || // Hash of ClientHello1
HelloRetryRequest ... MN)
The reason for this construction is to allow the server to do a
stateless HelloRetryRequest by storing just the hash of ClientHello1
in the cookie, rather than requiring it to export the entire
intermediate hash state (see Section 4.2.2).
In general, implementations can implement the transcript by keeping a
running transcript hash value based on the negotiated hash. Note,
however, that subsequent post-handshake authentications do not
include each other, just the messages through the end of the main
handshake.
4.4.2. Certificate
The server MUST send a Certificate message whenever the agreed-upon The server MUST send a Certificate message whenever the agreed-upon
key exchange method uses certificates for authentication (this key exchange method uses certificates for authentication (this
includes all key exchange methods defined in this document except includes all key exchange methods defined in this document except
PSK). This message conveys the endpoint's certificate chain to the PSK). This message conveys the endpoint's certificate chain to the
peer. peer.
The client MUST send a Certificate message if and only if the server The client MUST send a Certificate message if and only if the server
has requested client authentication via a CertificateRequest message has requested client authentication via a CertificateRequest message
(Section 4.3.2). If the server requests client authentication but no (Section 4.3.2). If the server requests client authentication but no
skipping to change at page 54, line 30 skipping to change at page 59, line 4
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} CertificateEntry; } CertificateEntry;
struct { struct {
opaque certificate_request_context<0..2^8-1>; opaque certificate_request_context<0..2^8-1>;
CertificateEntry certificate_list<0..2^24-1>; CertificateEntry certificate_list<0..2^24-1>;
} Certificate; } Certificate;
certificate_request_context If this message is in response to a certificate_request_context If this message is in response to a
CertificateRequest, the value of certificate_request_context in CertificateRequest, the value of certificate_request_context in
that message. Otherwise, in the case of server authentication that message. Otherwise (in the case of server authentication),
this field SHALL be zero length. this field SHALL be zero length.
certificate_list This is a sequence (chain) of CertificateEntry certificate_list This is a sequence (chain) of CertificateEntry
structures, each containing a single certificate and set of structures, each containing a single certificate and set of
extensions. The sender's certificate MUST come in the first extensions. The sender's certificate MUST come in the first
CertificateEntry in the list. Each following certificate SHOULD CertificateEntry in the list. Each following certificate SHOULD
directly certify one preceding it. Because certificate validation directly certify one preceding it. Because certificate validation
requires that trust anchors be distributed independently, a requires that trust anchors be distributed independently, a
certificate that specifies a trust anchor MAY be omitted from the certificate that specifies a trust anchor MAY be omitted from the
chain, provided that supported peers are known to possess any chain, provided that supported peers are known to possess any
omitted certificates. omitted certificates.
extensions: A set of extension values for the CertificateEntry. The extensions: A set of extension values for the CertificateEntry. The
"Extension" format is defined in Section 4.2. Valid extensions "Extension" format is defined in Section 4.2. Valid extensions
include OCSP Status extensions ([RFC6066] and [RFC6961]) and include OCSP Status extensions ([RFC6066] and [RFC6961]) and
SignedCertificateTimestamps ([RFC6962]). Any extension presented SignedCertificateTimestamps ([RFC6962]). An extension MUST only
in a Certificate message must only be presented if the be present in a Certificate message if the corresponding
corresponding ClientHello extension was presented in the initial ClientHello extension was presented in the initial handshake. If
handshake. If an extension applies the the entire chain, it an extension applies to the entire chain, it SHOULD be included in
SHOULD be included in the first CertificateEntry. the first CertificateEntry.
Note: Prior to TLS 1.3, "certificate_list" ordering required each Note: Prior to TLS 1.3, "certificate_list" ordering required each
certificate to certify the one immediately preceding it, however some certificate to certify the one immediately preceding it; however,
implementations allowed some flexibility. Servers sometimes send some implementations allowed some flexibility. Servers sometimes
both a current and deprecated intermediate for transitional purposes, send both a current and deprecated intermediate for transitional
and others are simply configured incorrectly, but these cases can purposes, and others are simply configured incorrectly, but these
nonetheless be validated properly. For maximum compatibility, all cases can nonetheless be validated properly. For maximum
implementations SHOULD be prepared to handle potentially extraneous compatibility, all implementations SHOULD be prepared to handle
certificates and arbitrary orderings from any TLS version, with the potentially extraneous certificates and arbitrary orderings from any
exception of the end-entity certificate which MUST be first. TLS version, with the 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.
4.4.1.1. OCSP Status and SCT Extensions 4.4.2.1. OCSP Status and SCT 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 replies with an empty extension to indicate negotiation of
extension and the OCSP information is carried in a CertificateStatus this extension and the OCSP information is carried in a
message. In TLS 1.3, the server's OCSP information is carried in an CertificateStatus message. In TLS 1.3, the server's OCSP information
extension in the CertificateEntry containing the associated is carried in an extension in the CertificateEntry containing the
certificate. Specifically: The body of the "status_request" or associated certificate. Specifically: The body of the
"status_request_v2" extension from the server MUST be a "status_request" extension from the server MUST be a
CertificateStatus structure as defined in [RFC6066] and [RFC6961] CertificateStatus structure as defined in [RFC6066].
respectively.
A server MAY request that a client present an OCSP response with its
certificate by sending a "status_request" extension in its
CertificateRequest message. If the client opts to send an OCSP
response, the body of its "status_request" extension MUST be a
CertificateStatus structure as defined in [RFC6066].
Similarly, [RFC6962] provides a mechanism for a server to send a Similarly, [RFC6962] provides a mechanism for a server to send a
Signed Certificate Timestamp (SCT) as an extension in the Signed Certificate Timestamp (SCT) as an extension in the
ServerHello. In TLS 1.3, the server's SCT information is carried in ServerHello. In TLS 1.3, the server's SCT information is carried in
an extension in CertificateEntry. an extension in CertificateEntry.
4.4.1.2. Server Certificate Selection 4.4.2.2. 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).
skipping to change at page 56, line 32 skipping to change at page 61, line 13
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 abort the handshake with an handshake, then it MUST abort the handshake with an
"unsupported_certificate" alert. "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).
4.4.1.3. Client Certificate Selection 4.4.2.3. Client Certificate Selection
The following rules apply to certificates sent by the client: The following rules apply to certificates sent by the client:
- 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 CertificateRequest
message was non-empty, one of the certificates in the certificate message was non-empty, at least one of the certificates in the
chain SHOULD be issued by one of the listed CAs. certificate 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 4.3.2. 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 CertificateRequest
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 4.3.2. 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.
4.4.1.4. Receiving a Certificate Message 4.4.2.4. 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
abort the handshake with a "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
skipping to change at page 57, line 40 skipping to change at page 62, line 21
signature algorithm using a SHA-1 hash abort the handshake with a signature algorithm using a SHA-1 hash abort the handshake with a
"bad_certificate" alert. All endpoints are RECOMMENDED to transition "bad_certificate" alert. All endpoints are RECOMMENDED to transition
to SHA-256 or better as soon as possible to maintain interoperability 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).
4.4.2. Certificate Verify 4.4.3. Certificate Verify
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 also possesses the private key corresponding to its certificate and also
provides integrity for the handshake up to this point. Servers MUST provides integrity for the handshake up to this point. Servers MUST
send this message when authenticating via a certificate. Clients send this message when authenticating via a certificate. Clients
MUST send this message whenever authenticating via a Certificate MUST send this message whenever authenticating via a certificate
(i.e., when the Certificate message is non-empty). When sent, this (i.e., when the Certificate message is non-empty). When sent, this
message MUST appear immediately after the Certificate Message and message MUST appear immediately after the Certificate message and
immediately prior to the Finished message. immediately prior to 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 4.2.3 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. The content to be signed is
described in Section 4.4 namely: the hash output as described in Section 4.4 namely:
Hash(Handshake Context + Certificate)
In TLS 1.3, the digital signature process takes as input:
- A signing key
- A context string
- The actual content to be signed Transcript-Hash(Handshake Context, Certificate)
The digital signature is then computed using the signing key over the The digital signature is then computed over the concatenation of:
concatenation of:
- 64 bytes of octet 32 - A string that consists of octet 32 (0x20) repeated 64 times
- The context string - The context string
- A single 0 byte which serves as the separator
- A single 0 byte which servers as the separator
- The content to be signed - The content to be signed
This structure is intended to prevent an attack on previous versions This structure is intended to prevent an attack on previous versions
of previous versions of TLS in which the ServerKeyExchange format of TLS in which the ServerKeyExchange format meant that attackers
meant that attackers could obtain a signature of a message with a could obtain a signature of a message with a chosen 32-byte prefix
chosen, 32-byte prefix. The initial 64 byte pad clears that prefix. (ClientHello.random). The initial 64-byte pad clears that prefix
along with the server-controlled ServerHello.random.
The context string for a server signature is "TLS 1.3, server The context string for a server signature is "TLS 1.3, server
CertificateVerify" and for a client signature is "TLS 1.3, client CertificateVerify" and for a client signature is "TLS 1.3, client
CertificateVerify". CertificateVerify". It is used to provide separation between
signatures made in different contexts, helping against potential
cross-protocol attacks.
For example, if Hash(Handshake Context + Certificate) was 32 bytes of For example, if the transcript hash was 32 bytes of 01 (this length
01 (this length would make sense for SHA-256), the input to the final would make sense for SHA-256), the content covered by the digital
signing process for a server CertificateVerify would be: signature for a server CertificateVerify would be:
2020202020202020202020202020202020202020202020202020202020202020 2020202020202020202020202020202020202020202020202020202020202020
2020202020202020202020202020202020202020202020202020202020202020 2020202020202020202020202020202020202020202020202020202020202020
544c5320312e332c207365727665722043657274696669636174655665726966 544c5320312e332c207365727665722043657274696669636174655665726966
79 79
00 00
0101010101010101010101010101010101010101010101010101010101010101 0101010101010101010101010101010101010101010101010101010101010101
If sent by a server, the signature algorithm MUST be one offered in On the sender side the process for computing the signature field of
the client's "signature_algorithms" extension unless no valid the CertificateVerify message takes as input:
certificate chain can be produced without unsupported algorithms (see
Section 4.2.3). - The content covered by the digital signature
- The private signing key corresponding to the certificate sent in
the previous message
If the CertificateVerify message is sent by a server, the signature
algorithm MUST be one offered in the client's "signature_algorithms"
extension unless no valid certificate chain can be produced without
unsupported algorithms (see 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
algorithms in this specification are defined solely for use in legacy algorithms in this specification are defined solely for use in legacy
certificates, and are not valid for CertificateVerify signatures. certificates, and are not valid for CertificateVerify signatures.
The receiver of a CertificateVerify MUST verify the signature field.
The verification process takes as input:
- The content covered by the digital signature
- The public key contained in the end-entity certificate found in
the associated Certificate message.
- The digital signature received in the signature field of the
CertificateVerify message
If the verification fails, the receiver MUST terminate the handshake
with a "decrypt_error" alert.
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. When the PSK was established through a NewSessionTicket, directly. When the PSK was established through a NewSessionTicket,
the client's signature transitively covers the server's certificate the client's signature transitively covers the server's certificate
through the PSK binder. [PSK-FINISHED] describes a concrete attack through the PSK binder. [PSK-FINISHED] describes a concrete attack
on constructions that do not bind to the server's certificate. It is on constructions that do not bind to the server's certificate. It is
unsafe to use certificate-based client authentication when the client unsafe to use certificate-based client authentication when the client
might potentially share the same PSK/key-id pair with two different might potentially share the same PSK/key-id pair with two different
endpoints and implementations MUST NOT combine external PSKs with endpoints and implementations MUST NOT combine external PSKs with
certificate-based authentication. certificate-based authentication.
4.4.3. Finished 4.4.4. Finished
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 handshake block. It is essential for providing authentication of the handshake
and of the computed keys. and of the computed keys.
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 and correct and if incorrect MUST terminate the connection with a
validated the Finished message from its peer, it may begin to send "decrypt_error" alert.
and receive application data over the connection.
Once a side has sent its Finished message and received and validated
the Finished message from its peer, it may begin to send and receive
application data over the connection. Early data may be sent prior
to the receipt of the peer's Finished message, per Section 4.2.7.
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 4.4 using HKDF (see Section 7.1). Base key defined in Section 4.4 using HKDF (see Section 7.1).
Specifically: Specifically:
finished_key = finished_key =
HKDF-Expand-Label(BaseKey, "finished", "", Hash.length) HKDF-Expand-Label(BaseKey, "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 =
HMAC(finished_key, Hash( HMAC(finished_key,
Handshake Context + Transcript-Hash(Handshake Context,
Certificate* + Certificate*, CertificateVerify*))
CertificateVerify*
)
)
* Only included if present. * Only included if present.
Where HMAC [RFC2104] uses the Hash algorithm for the handshake. As Where HMAC [RFC2104] uses the Hash algorithm for the handshake. As
noted above, the HMAC input can generally be implemented by a running noted above, the HMAC input can generally be implemented by a running
hash, i.e., just the handshake hash at this point. hash, i.e., just the handshake hash at this point.
In previous versions of TLS, the verify_data was always 12 octets In previous versions of TLS, the verify_data was always 12 octets
long. In the current version of TLS, it is the size of the HMAC long. In TLS 1.3, it is the size of the HMAC output for the Hash
output for the Hash used for the handshake. 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 appropriate application traffic key as described in
alerts sent by the server in response to client Certificate and Section 7.2. In particular, this includes any alerts sent by the
CertificateVerify messages. server in response to client Certificate and CertificateVerify
messages.
4.5. Post-Handshake Messages 4.5. End of Early Data
struct {} EndOfEarlyData;
The EndOfEarlyData message is sent by the client to indicate that all
0-RTT application_data messages have been transmitted (or none will
be sent at all) and that the following records are protected under
handshake traffic keys. Servers MUST NOT send this message and
clients receiving it MUST terminate the connection with an
"unexpected_message" alert. This message is encrypted under keys
derived from the client_early_traffic_secret.
4.6. 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 appropriate application traffic key.
Handshake messages sent after the handshake MUST NOT be interleaved
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
them.
4.5.1. New Session Ticket Message 4.6.1. 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 resumption master secret. the resumption master secret.
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 4.2.6). Servers MAY send multiple tickets on a single (Section 4.2.8). 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.
Any ticket MUST only be resumed with a cipher suite that has the same Any ticket MUST only be resumed with a cipher suite that has the same
KDF hash as that used to establish the original connection, and if KDF hash as that used to establish the original connection, and only
the client provides the same SNI value as described in Section 3 of if the client provides the same SNI value as in the original
[RFC6066]. connection, as described in Section 3 of [RFC6066].
Note: Although the resumption master secret depends on the client's Note: Although the resumption master secret depends on the client's
second flight, servers which do not request client authentication MAY second flight, servers which do not request client authentication MAY
compute the remainder of the transcript independently and then send a compute the remainder of the transcript independently and then send a
NewSessionTicket immediately upon sending its Finished rather than NewSessionTicket immediately upon sending its Finished rather than
waiting for the client Finished. waiting for the client Finished. This might be appropriate in cases
where the client is expected to open multiple TLS connections in
parallel and would benefit from the reduced overhead of a resumption
handshake, for example.
struct { struct {
uint32 ticket_lifetime; uint32 ticket_lifetime;
uint32 ticket_age_add; uint32 ticket_age_add;
opaque ticket<1..2^16-1>; opaque ticket<1..2^16-1>;
Extension extensions<0..2^16-2>; Extension extensions<0..2^16-2>;
} NewSessionTicket; } NewSessionTicket;
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
(7 days). The value of zero indicates that the ticket should be (7 days). The value of zero indicates that the ticket should be
discarded immediately. Clients MUST NOT cache session tickets for discarded immediately. Clients MUST NOT cache tickets for longer
longer than 7 days, regardless of the ticket_lifetime. It MAY than 7 days, regardless of the ticket_lifetime, and MAY delete the
delete the ticket earlier based on local policy. A server MAY ticket earlier based on local policy. A server MAY treat a ticket
treat a ticket as valid for a shorter period of time than what is as valid for a shorter period of time than what is stated in the
stated in the ticket_lifetime. ticket_lifetime.
ticket_age_add A randomly generated 32-bit value that is used to ticket_age_add A securely generated, random 32-bit value that is
obscure the age of the ticket that the client includes in the used to obscure the age of the ticket that the client includes in
"early_data" extension. The client-side ticket age is added to the "pre_shared_key" extension. The client-side ticket age is
this value modulo 2^32 to obtain the value that is transmitted by added to this value modulo 2^32 to obtain the value that is
the client. transmitted by the client.
ticket The value of the ticket to be used as the PSK identifier. ticket The value of the ticket to be used as the PSK identity. The
The ticket itself is an opaque label. It MAY either be a database ticket itself is an opaque label. It MAY either be a database
lookup key or a self-encrypted and self-authenticated value. lookup key or a self-encrypted and self-authenticated value.
Section 4 of [RFC5077] describes a recommended ticket construction Section 4 of [RFC5077] describes a recommended ticket construction
mechanism. mechanism.
extensions A set of extension values for the ticket. The extensions A set of extension values for the ticket. The
"Extension" format is defined in Section 4.2. Clients MUST ignore "Extension" format is defined in Section 4.2. Clients MUST ignore
unrecognized extensions. unrecognized extensions.
This document defines one ticket extension, "ticket_early_data_info" The sole extension currently defined for NewSessionTicket is
"early_data", indicating that the ticket may be used to send 0-RTT
struct { data (Section 4.2.7)). It contains the following value:
uint32 max_early_data_size;
} TicketEarlyDataInfo;
This extension indicates that the ticket may be used to send 0-RTT
data (Section 4.2.8)). It contains the following value:
max_early_data_size The maximum amount of 0-RTT data that the client max_early_data_size The maximum amount of 0-RTT data that the client
is allowed to send when using this ticket, in bytes. Only is allowed to send when using this ticket, in bytes. Only
Application Data payload is counted. A server receiving more than Application Data payload (i.e., plaintext but not padding or the
inner content type byte) is counted. A server receiving more than
max_early_data_size bytes of 0-RTT data SHOULD terminate the max_early_data_size bytes of 0-RTT data SHOULD terminate the
connection with an "unexpected_message" alert. connection with an "unexpected_message" alert.
4.5.2. Post-Handshake Authentication Note that in principle it is possible to continue issuing new tickets
which continue to indefinitely extend the lifetime of the keying
material originally derived from an initial non-PSK handshake (which
was most likely tied to the peer's certificate). It is RECOMMENDED
that implementations place limits on the total lifetime of such
keying material; these limits should take into account the lifetime
of the peer's certificate, the likelihood of intervening revocation,
and the time since the peer's online CertificateVerify signature.
4.6.2. 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).
4.5.3. Key and IV Update 4.6.3. Key and IV Update
enum { enum {
update_not_requested(0), update_requested(1), (255) update_not_requested(0), update_requested(1), (255)
} KeyUpdateRequest; } KeyUpdateRequest;
struct { struct {
KeyUpdateRequest request_update; KeyUpdateRequest request_update;
} KeyUpdate; } KeyUpdate;
request_update Indicates that the recipient of the KeyUpdate should request_update Indicates whether the recipient of the KeyUpdate
respond with its own KeyUpdate. If an implementation receives any should respond with its own KeyUpdate. If an implementation
other value, it MUST terminate the connection with an receives any other value, it MUST terminate the connection with an
"illegal_parameter" alert. "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 either peer after it has sent a Finished message. Implementations
sending its second flight. Implementations that receive a KeyUpdate that receive a KeyUpdate message prior to receiving a Finished
message prior to receiving a Finished message as part of the 1-RTT message MUST terminate the connection with an "unexpected_message"
handshake MUST terminate the connection with an "unexpected_message"
alert. After sending a KeyUpdate message, the sender SHALL send all alert. After sending a KeyUpdate message, the sender SHALL send all
its traffic using the next generation of keys, computed as described its traffic using the next generation of keys, computed as described
in Section 7.2. Upon receiving a KeyUpdate, the receiver MUST update in Section 7.2. Upon receiving a KeyUpdate, the receiver MUST update
its receiving keys. its receiving keys.
If the request_udate field is set to "update_requested" then the If the request_update field is set to "update_requested" then the
receiver MUST send a KeyUpdate of its own with request_update set to receiver MUST send a KeyUpdate of its own with request_update set to
"update_not_requested" prior to sending its next application data "update_not_requested" prior to sending its next application data
record. This mechanism allows either side to force an update to the record. This mechanism allows either side to force an update to the
entire connection, but causes an implementation which receives entire connection, but causes an implementation which receives
multiple KeyUpdates while it is silent to respond with a single multiple KeyUpdates while it is silent to respond with a single
update. Note that implementations may receive an arbitrary number of update. Note that implementations may receive an arbitrary number of
messages between sending a KeyUpdate and receiving the peer's messages between sending a KeyUpdate with request_update set to
KeyUpdate because those messages may already be in flight. However, update_requested and receiving the peer's KeyUpdate, because those
because send and receive keys are derived from independent traffic messages may already be in flight. However, because send and receive
secrets, retaining the receive traffic secret does not threaten the keys are derived from independent traffic secrets, retaining the
forward secrecy of data sent before the sender changed keys. receive traffic secret does not threaten the forward secrecy of data
sent before the sender changed keys.
If implementations independently send their own KeyUpdates with If implementations independently send their own KeyUpdates with
request_update set to "update_requested", and they cross in flight, request_update set to "update_requested", and they cross in flight,
then each side will also send a response, with the result that each then each side will also send a response, with the result that each
side increments by two generations. 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.
4.6. Handshake Layer and Key Changes
Handshake messages MUST NOT span key changes. Because the
ServerHello, Finished, and KeyUpdate messages signal a key change,
upon receiving these messages a receiver MUST verify that the end of
these messages aligns with a record boundary; if not, then it MUST
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 verified and decrypted, 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 terminate implementation receives an unexpected record type, it MUST terminate
the connection with an "unexpected_message" alert. New record the connection with an "unexpected_message" alert. New record
content type values are assigned by IANA in the TLS Content Type content type values are assigned by IANA in the TLS Content Type
Registry as described in Section 10. Registry as described in Section 10.
Application Data messages are carried by the record layer and are
fragmented and encrypted as described below. The messages are
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
in non-empty blocks of arbitrary size.
The record layer fragments information blocks into TLSPlaintext The record layer fragments information blocks into TLSPlaintext
records carrying data in chunks of 2^14 bytes or less. 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 handled differently depending on the underlying
messages of the same ContentType MAY be coalesced into a single ContentType. Any future content types MUST specify appropriate
TLSPlaintext record, or a single message MAY be fragmented across rules. Note that these rules are stricter than what was enforced in
several records). Alert messages (Section 6) MUST NOT be fragmented TLS 1.2.
across records.
enum { Handshake messages MAY be coalesced into a single TLSPlaintext record
alert(21), or fragmented across several records, provided that:
handshake(22),
application_data(23),
(255)
} ContentType;
struct { - Handshake messages MUST NOT be interleaved with other record
ContentType type; types. That is, if a handshake message is split over two or more
ProtocolVersion legacy_record_version = 0x0301; /* TLS v1.x */ records, there MUST NOT be any other records between them.
uint16 length;
opaque fragment[TLSPlaintext.length]; - Handshake messages MUST NOT span key changes. Because the
} TLSPlaintext; ClientHello, EndOfEarlyData, ServerHello, Finished, and KeyUpdate
messages can arrive immediately prior to a key change, upon
receiving these messages a receiver MUST verify that the end of
these messages aligns with a record boundary; if not, then it MUST
terminate the connection with an "unexpected_message" alert.
Implementations MUST NOT send zero-length fragments of Handshake
types, even if those fragments contain padding.
Alert messages (Section 6) MUST NOT be fragmented across records and
multiple Alert messages MUST NOT be coalesced into a single
TLSPlaintext record. In other words, a record with an Alert type
MUST contain exactly one message.
Application Data messages contain data that is opaque to TLS.
Application Data messages are always protected. Zero-length
fragments of Application Data MAY be sent as they are potentially
useful as a traffic analysis countermeasure.
enum {
alert(21),
handshake(22),
application_data(23),
(255)
} ContentType;
struct {
ContentType type;
ProtocolVersion legacy_record_version;
uint16 length;
opaque fragment[TLSPlaintext.length];
} TLSPlaintext;
type The higher-level protocol used to process the enclosed type The higher-level protocol used to process the enclosed
fragment. fragment.
legacy_record_version This value MUST be set to 0x0301 for all legacy_record_version This value MUST be set to 0x0301 for all
records. This field is deprecated and MUST be ignored for all records generated by a TLS 1.3 implementation. This field is
purposes. deprecated and MUST be ignored for all purposes. Previous
versions of TLS would use other values in this field under some
circumstances.
length The length (in bytes) of the following TLSPlaintext.fragment. length The length (in bytes) of the following TLSPlaintext.fragment.
The length MUST NOT exceed 2^14. An endpoint that receives a The length MUST NOT exceed 2^14 bytes. An endpoint that receives
record that exceeds this length MUST terminate the connection with a record that exceeds this length MUST terminate the connection
a "record_overflow" alert. with a "record_overflow" alert.
fragment The data being transmitted. This value transparent and fragment The data being transmitted. This value is transparent and
treated as an independent block to be dealt with by the higher- is treated as an independent block to be dealt with by the higher-
level protocol specified by the type field. level protocol specified by the type field.
This document describes TLS Version 1.3, which uses the version This document describes TLS 1.3, which uses the version 0x0304. This
0x0304. This version value is historical, deriving from the use of version value is historical, deriving from the use of 0x0301 for TLS
0x0301 for TLS 1.0 and 0x0300 for SSL 3.0. In order to maximize 1.0 and 0x0300 for SSL 3.0. In order to maximize backwards
backwards compatibility, the record layer version identifies as compatibility, the record layer version identifies as simply TLS 1.0.
simply TLS 1.0. Endpoints supporting other versions negotiate the Endpoints supporting multiple versions negotiate the version to use
version to use by following the procedure and requirements in by following the procedure and requirements in Appendix D.
Appendix C.
Implementations MUST NOT send zero-length fragments of Handshake or
Alert types, even if those fragments contain padding. Zero-length
fragments of Application Data MAY be sent as they are potentially
useful as a traffic analysis countermeasure.
When record protection has not yet been engaged, TLSPlaintext When record protection has not yet been engaged, TLSPlaintext
structures are written directly onto the wire. Once record structures are written directly onto the wire. Once record
protection has started, TLSPlaintext records are protected and sent protection has started, TLSPlaintext records are protected and sent
as described in the following section. as described in the following section.
5.2. Record Payload Protection 5.2. Record Payload Protection
The record protection functions translate a TLSPlaintext structure The record protection functions translate a TLSPlaintext structure
into a TLSCiphertext. The deprotection functions reverse the into a TLSCiphertext. The deprotection functions reverse the
process. In TLS 1.3 as opposed to previous versions of TLS, all process. In TLS 1.3, as opposed to previous versions of TLS, all
ciphers are modeled as "Authenticated Encryption with Additional ciphers are modeled as "Authenticated Encryption with Additional
Data" (AEAD) [RFC5116]. AEAD functions provide a unified encryption Data" (AEAD) [RFC5116]. AEAD functions provide an unified encryption
and authentication operation which turns plaintext into authenticated and authentication operation which turns plaintext into authenticated
ciphertext and back again. Each encrypted record consists of a ciphertext and back again. Each encrypted record consists of a
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 = 23; /* application_data */ ContentType opaque_type = 23; /* application_data */
ProtocolVersion legacy_record_version = 0x0301; /* TLS v1.x */ ProtocolVersion legacy_record_version = 0x0301; /* 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 byte encoding of a handshake or an alert message, or the
raw bytes of the application's data to send.
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 TLSInnerPlaintext.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 always
to TLSPlaintext.legacy_record_version and is always 0x0301. Note 0x0301. TLS 1.3 TLSCiphertexts are not generated until after TLS
that the handshake protocol including the ClientHello and 1.3 has been negotiated, so there are no historical compatibility
ServerHello messages authenticates the protocol version, so this concerns where other values might be received. Implementations
value is redundant. MAY verify that the legacy_record_version field is 0x0301 and
abort the connection if it is not. Note that the handshake
protocol including the ClientHello and ServerHello messages
authenticates the protocol version, so this 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.encrypted_record, which is the sum of the lengths of
content and the padding, plus one for the inner content type. The the content and the padding, plus one for the inner content type,
length MUST NOT exceed 2^14 + 256. An endpoint that receives a plus any expansion added by the AEAD algorithm. The length MUST
record that exceeds this length MUST terminate the connection with NOT exceed 2^14 + 256 bytes. An endpoint that receives a record
a "record_overflow" alert. that exceeds this length MUST terminate the connection with 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 algorithms 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 TLSInnerPlaintext.fragment,
TLSPlaintext.type, and any padding bytes (zeros). TLSInnerPlaintext.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 from 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 TLSInnerPlaintext.length due to the inclusion of
however much padding is supplied by the sender. The length of the TLSInnerPlaintext.type and any padding supplied by the sender. The
AEAD output will generally be larger than the plaintext, but by an length of the AEAD output will generally be larger than the
amount that varies with the AEAD algorithm. Since the ciphers might plaintext, but by an amount that varies with the AEAD algorithm.
incorporate padding, the amount of overhead could vary with different
lengths of plaintext. Symbolically, Since the ciphers might incorporate padding, the amount of overhead
could vary with different 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 encrypted_record =
AEAD-Decrypt(write_key, nonce, AEADEncrypted) AEAD-Decrypt(write_key, nonce, AEADEncrypted)
If the decryption fails, the receiver MUST terminate the connection If the decryption fails, the receiver MUST terminate the connection
with a "bad_record_mac" alert. with a "bad_record_mac" alert.
An AEAD algorithm used in TLS 1.3 MUST NOT produce an expansion of An AEAD algorithm used in TLS 1.3 MUST NOT produce an expansion
greater than 255 bytes. An endpoint that receives a record from its greater than 255 octets. An endpoint that receives a record from its
peer with TLSCipherText.length larger than 2^14 + 256 octets MUST peer with TLSCipherText.length larger than 2^14 + 256 octets MUST
terminate the connection with a "record_overflow" alert. This limit terminate the connection with a "record_overflow" alert. This limit
is derived from the maximum TLSPlaintext length of 2^14 octets + 1 is derived from the maximum TLSPlaintext length of 2^14 octets + 1
octet for ContentType + 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 by one after reading or writing
record. The first record transmitted under a particular set of each record. The first record transmitted under a particular set of
traffic keys record key MUST use sequence number 0. traffic keys MUST use sequence number 0.
Sequence numbers do not wrap. If a TLS implementation would need to Because the size of sequence numbers is 64-bit, they should not wrap.
wrap a sequence number, it MUST either rekey (Section 4.5.3) or If a TLS implementation would need to wrap a sequence number, it MUST
terminate the connection. either re-key (Section 4.6.3) or terminate the connection.
The length of the per-record nonce (iv_length) is set to max(8 bytes, Each AEAD algorithm will specify a range of possible lengths for the
N_MIN) for the AEAD algorithm (see [RFC5116] Section 4). An AEAD per-record nonce, from N_MIN bytes to N_MAX bytes of input
algorithm where N_MAX is less than 8 bytes MUST NOT be used with TLS. ([RFC5116]). The length of the TLS per-record nonce (iv_length) is
The per-record nonce for the AEAD construction is formed as follows: set to the larger of 8 bytes and 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. 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 encoded in network byte
zeroes to iv_length. order and padded to the left with zeros to iv_length.
2. The padded sequence number is XORed with the static 2. The padded sequence number is XORed with the static
client_write_iv or server_write_iv, depending on the role. client_write_iv or server_write_iv, depending on the role.
The resulting quantity (of length iv_length) is used as the per- The resulting quantity (of length iv_length) is used as the per-
record nonce. record nonce.
Note: This is a different construction from that in TLS 1.2, which Note: This is a different construction from that in TLS 1.2, which
specified a partially explicit nonce. specified a partially explicit nonce.
skipping to change at page 69, line 7 skipping to change at page 74, line 31
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 Application Data records may contain a zero-length
TLSInnerPlaintext.content if the sender desires. This permits TLSInnerPlaintext.content if the sender desires. This permits
generation of plausibly-sized cover traffic in contexts where the generation of plausibly-sized cover traffic in contexts where the
presence or absence of activity may be sensitive. Implementations presence or absence of activity may be sensitive. Implementations
MUST NOT send Handshake or Alert records that have a zero-length MUST NOT send Handshake or Alert records that have a zero-length
TLSInnerPlaintext.content. TLSInnerPlaintext.content; if such a message is received, the
receiving implementation MUST terminate the connection with an
"unexpected_message" alert.
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
the receiving implementation scans the field from the end toward the TLSCiphertext.encrypted_record, the receiving implementation scans
beginning until it finds a non-zero octet. This non-zero octet is the field from the end toward the beginning until it finds a non-zero
the content type of the message. This padding scheme was selected octet. This non-zero octet is the content type of the message. This
because it allows padding of any encrypted TLS record by an arbitrary padding scheme was selected because it allows padding of any
size (from zero up to TLS record size limits) without introducing new encrypted TLS record by an arbitrary size (from zero up to TLS record
content types. The design also enforces all-zero padding octets, size limits) without introducing new content types. The design also
which allows for quick detection of padding errors. enforces all-zero padding octets, 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 MUST terminate the find a non-zero octet in the cleartext, it MUST terminate the
connection with an "unexpected_message" alert. connection with an "unexpected_message" 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
skipping to change at page 69, line 43 skipping to change at page 75, line 21
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 4.5.3 prior to Implementations SHOULD do a key update as described in Section 4.6.3
reaching these limits. prior to reaching these limits.
For AES-GCM, up to 2^24.5 full-size records (about 24 million) may be For AES-GCM, up to 2^24.5 full-size records (about 24 million) may be
encrypted on a given connection while keeping a safety margin of encrypted on a given connection while keeping a safety margin of
approximately 2^-57 for Authenticated Encryption (AE) security. For approximately 2^-57 for Authenticated Encryption (AE) security. For
ChaCha20/Poly1305, the record sequence number would wrap before the ChaCha20/Poly1305, the record sequence number would wrap before the
safety limit is 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 a description of the alert and a legacy field
and a description of the alert. Warning-level messages are used to that conveyed the severity of the message in previous versions of
indicate orderly closure of the connection or the end of early data TLS. In TLS 1.3, the severity is implicit in the type of alert being
(see Section 6.1). Upon receiving a warning-level alert, the TLS sent, and can safely be ignored. Some alerts are sent to indicate
implementation SHOULD indicate end-of-data to the application and, if orderly closure of the connection or the end of early data (see
appropriate for the alert type, send a closure alert in response. Section 6.1). Upon receiving such an alert, the TLS implementation
SHOULD indicate end-of-data to the application, and if appropriate
for the alert type, send a closure alert in response.
Fatal-level messages are used to indicate abortive closure of the Error alerts indicate abortive closure of the connection (see
connection (See Section 6.2). Upon receiving a fatal-level alert, Section 6.2). Upon receiving an error alert, the TLS implementation
the TLS implementation SHOULD indicate an error to the application SHOULD indicate an error to the application and MUST NOT allow any
and MUST NOT allow any further data to be sent or received on the further data to be sent or received on the connection. Servers and
connection. Servers and clients MUST forget keys and secrets clients MUST forget keys and secrets associated with a failed
associated with a failed connection. Stateful implementations of connection. Stateful implementations of tickets (as in many clients)
session tickets (as in many clients) SHOULD discard tickets SHOULD discard tickets associated with failed connections.
associated with failed connections.
All the alerts listed in Section 6.2 MUST be sent as fatal and MUST All the alerts listed in Section 6.2 MUST be sent as fatal and MUST
be treated as fatal regardless of the AlertLevel in the message. be treated as fatal regardless of the AlertLevel in the message.
Unknown alert types MUST be treated as fatal. Unknown alert types MUST be treated as fatal.
enum { warning(1), fatal(2), (255) } AlertLevel; enum { warning(1), fatal(2), (255) } AlertLevel;
enum { enum {
close_notify(0), close_notify(0),
end_of_early_data(1),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
record_overflow(22), record_overflow(22),
handshake_failure(40), handshake_failure(40),
bad_certificate(42), bad_certificate(42),
unsupported_certificate(43), unsupported_certificate(43),
certificate_revoked(44), certificate_revoked(44),
certificate_expired(45), certificate_expired(45),
certificate_unknown(46), certificate_unknown(46),
illegal_parameter(47), illegal_parameter(47),
skipping to change at page 71, line 48 skipping to change at page 76, line 51
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
6.1. Closure Alerts 6.1. Closure Alerts
The client and the server must share knowledge that the connection is The client and the server must share knowledge that the connection is
ending in order to avoid a truncation attack. Failure to properly ending in order to avoid a truncation attack.
close a connection does not prohibit a session from being resumed.
close_notify This alert notifies the recipient that the sender will close_notify This alert notifies the recipient that the sender will
not send any more messages on this connection. Any data received not send any more messages on this connection. Any data received
after a closure MUST be ignored. after a closure MUST be ignored.
end_of_early_data This alert is sent by the client to indicate that
all 0-RTT application_data messages have been transmitted (or none
will be sent at all) and that this is the end of the flight. This
alert MUST be at the warning level. Servers MUST NOT send this
alert and clients receiving it MUST terminate the connection with
an "unexpected_message" alert.
user_canceled This alert notifies the recipient that the sender is user_canceled This alert notifies the recipient that the sender is
canceling the handshake for some reason unrelated to a protocol canceling the handshake for some reason unrelated to a protocol
failure. If a user cancels an operation after the handshake is failure. If a user cancels an operation after the handshake is
complete, just closing the connection by sending a "close_notify" complete, just closing the connection by sending a "close_notify"
is more appropriate. This alert SHOULD be followed by a is more appropriate. This alert SHOULD be followed by a
"close_notify". This alert is generally a warning. "close_notify". This alert is generally a warning.
Either party MAY initiate a close by sending a "close_notify" alert. Either party MAY initiate a close by sending a "close_notify" alert.
Any data received after a closure alert is ignored. If a transport- Any data received after a closure alert MUST be ignored. If a
level close is received prior to a "close_notify", the receiver transport-level close is received prior to a "close_notify", the
cannot know that all the data that was sent has been received. receiver cannot know that all the data that was sent has been
received.
Each party MUST send a "close_notify" alert before closing the write Each party MUST send a "close_notify" alert before closing the write
side of the connection, unless some other fatal alert has been side of the connection, unless some other fatal alert has been
transmitted. The other party MUST respond with a "close_notify" transmitted. The other party MUST respond with a "close_notify"
alert of its own and close down the connection immediately, alert of its own and close down the connection immediately,
discarding any pending writes. The initiator of the close need not discarding any pending writes. The initiator of the close need not
wait for the responding "close_notify" alert before closing the read wait for the responding "close_notify" alert before closing the read
side of the connection. side of the connection.
If the application protocol using TLS provides that any data may be If the application protocol using TLS provides that any data may be
carried over the underlying transport after the TLS connection is carried over the underlying transport after the TLS connection is
closed, the TLS implementation must receive the responding closed, the TLS implementation MUST receive the responding
"close_notify" alert before indicating to the application layer that "close_notify" alert before indicating to the application layer that
the TLS connection has ended. If the application protocol will not the TLS connection has ended. If the application protocol will not
transfer any additional data, but will only close the underlying transfer any additional data, but will only close the underlying
transport connection, then the implementation MAY choose to close the transport connection, then the implementation MAY choose to close the
transport without waiting for the responding "close_notify". No part transport without waiting for the responding "close_notify". No part
of this standard should be taken to dictate the manner in which a of this standard should be taken to dictate the manner in which a
usage profile for TLS manages its data transport, including when usage profile for TLS manages its data transport, including when
connections are opened or closed. connections are opened or closed.
Note: It is assumed that closing a connection reliably delivers Note: It is assumed that closing a connection reliably delivers
pending data before destroying the transport. pending data before destroying the transport.
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. MUST immediately close the connection.
Whenever an implementation encounters a fatal error condition, it Whenever an implementation encounters a fatal error condition, it
SHOULD send an appropriate fatal alert and MUST close the connection SHOULD send an appropriate fatal alert and MUST close the connection
without sending or receiving any additional data. In the rest of without sending or receiving any additional data. In the rest of
this specification, the phrase "{terminate the connection, abort the this specification, when the phrases "terminate the connection" and
handshake}" is used without a specific alert means that the "abort the handshake" are used without a specific alert it means that
implementation SHOULD send the alert indicated by the descriptions the implementation SHOULD send the alert indicated by the
below. The phrase "{terminate the connection, abort the handshake} descriptions below. The phrases "terminate the connection with a X
with a X alert" MUST send alert X if it sends any alert. All alerts alert" and "abort the handshake with a X alert" mean that the
defined in this section below, as well as all unknown alerts are implementation 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). 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 (e.g., the wrong unexpected_message An inappropriate message (e.g., the wrong
handshake message, premature application data, etc.) was received. handshake message, premature application data, etc.) was received.
This alert should never be observed in communication between This alert should never be observed in communication between
proper implementations. 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, and also to avoid side channel attacks, this
failures. This alert should never be observed in communication alert is used for all deprotection failures. This alert should
between proper implementations, except when messages were never be observed in communication between proper implementations,
corrupted in the network. except when messages were 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
TLSPlaintext record with more than 2^14 bytes. This alert should TLSPlaintext record with more than 2^14 bytes. This alert should
never be observed in communication between proper implementations, never be observed in communication between proper implementations,
except when messages were corrupted in the network. except when messages were corrupted in the network.
handshake_failure Reception of a "handshake_failure" alert message handshake_failure Reception of a "handshake_failure" alert message
indicates that the sender was unable to negotiate an acceptable indicates that the sender was unable to negotiate an acceptable
set of security parameters given the options available. set of security parameters given the options available.
skipping to change at page 74, line 18 skipping to change at page 79, line 12
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 incorrect or illegal_parameter A field in the handshake was incorrect or
inconsistent with other fields. This alert is used for errors inconsistent with other fields. This alert is used for errors
which conform to the formal protocol syntax but are otherwise which conform to the formal protocol syntax but are otherwise
incorrect. 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 could not be matched with a known trust
CA. anchor.
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 is used for errors where the message does incorrect. This alert is used for errors where the message does
not conform to the formal protocol syntax. This alert should not conform to the formal protocol syntax. This alert should
never be observed in communication between proper implementations, never be observed in communication between proper implementations,
except when messages were corrupted in the network. 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 or a PSK binder. Finished message or a PSK binder.
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 D)
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
parameters more secure than those supported by the client. parameters more secure than those supported by the client.
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 or other negotiated parameters. TLS version or other negotiated parameters.
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
or Certificate not first offered in the corresponding ClientHello. or Certificate 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 (see [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]. (see [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]. "status_request" extension (see [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 (see [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 certificate_required Sent by servers when a client certificate is
desired but none was provided by the client. desired but none was provided by the client.
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 The TLS handshake establishes one or more input secrets which are
requires specification of a suite of algorithms, a master secret, and combined to create the actual working keying material, as detailed
the client and server random values. below. The key derivation process incorporates both the input
secrets and the handshake transcript. Note that because the
handshake transcript includes the random values in the Hello
messages, any given handshake will have different traffic secrets,
even if the same input secrets are used, as is the case when the same
PSK is used for multiple connections
7.1. Key Schedule 7.1. Key Schedule
The TLS handshake establishes one or more input secrets which are The key derivation process makes use of the HKDF-Extract and HKDF-
combined to create the actual working keying material, as detailed Expand functions as defined for HKDF [RFC5869], as well as the
below. The key derivation process makes use of the HKDF-Extract and
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 { struct {
uint16 length = Length; uint16 length = Length;
opaque label<9..255> = "TLS 1.3, " + Label; opaque label<10..255> = "TLS 1.3, " + Label;
opaque hash_value<0..255> = HashValue; opaque hash_value<0..255> = HashValue;
} HkdfLabel; } HkdfLabel;
Derive-Secret(Secret, Label, Messages) = Derive-Secret(Secret, Label, Messages) =
HKDF-Expand-Label(Secret, Label, HKDF-Expand-Label(Secret, Label,
Hash(Messages), Hash.Length) Transcript-Hash(Messages), 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
algorithm. Hash.length is its output length. algorithm. Hash.length is its output length in bytes. Messages are
the concatenation of the indicated handshake messages, including the
handshake message type and length fields, but not including record
layer headers. Note that in some cases a zero-length HashValue
(indicated by "") is passed to HKDF-Expand-Label.
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
as long as the size of the Hash that is the basis for the HKDF. Hash.length zero bytes. Concretely, for the present version of TLS
Concretely, for the present version of TLS 1.3, secrets are added in 1.3, secrets are added in the following order:
the following order:
- PSK - PSK (a pre-shared key established externally or a
resumption_master_secret value from a previous connection)
- (EC)DHE shared secret - (EC)DHE shared secret (Section 7.4)
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 incoming
in from the left. For instance, the Early Secret is the Secret arrow. For instance, the Early Secret is the Secret for
for generating the client_early_traffic_secret. generating the client_early_traffic_secret.
0 0
| |
v v
PSK -> HKDF-Extract PSK -> HKDF-Extract = Early Secret
|
v
Early Secret
| |
+------> Derive-Secret(., +-----> Derive-Secret(.,
| "external psk binder key" | | "external psk binder key" |
| "resumption psk binder key", | "resumption psk binder key",
| "") | "")
| = binder_key | = binder_key
| |
+------> Derive-Secret(., "client early traffic secret", +-----> Derive-Secret(., "client early traffic secret",
| ClientHello) | ClientHello)
| = client_early_traffic_secret | = client_early_traffic_secret
| |
+-----> Derive-Secret(., "early exporter master secret", +-----> Derive-Secret(., "early exporter master secret",
| ClientHello) | ClientHello)
| = early_exporter_secret | = early_exporter_secret
v v
(EC)DHE -> HKDF-Extract Derive-Secret(., "derived secret", "")
| |
v v
Handshake Secret (EC)DHE -> HKDF-Extract = Handshake Secret
| |
+-----> Derive-Secret(., "client handshake traffic secret", +-----> Derive-Secret(., "client handshake traffic secret",
| ClientHello...ServerHello) | ClientHello...ServerHello)
| = client_handshake_traffic_secret | = client_handshake_traffic_secret
| |
+-----> Derive-Secret(., "server handshake traffic secret", +-----> Derive-Secret(., "server handshake traffic secret",
| ClientHello...ServerHello) | ClientHello...ServerHello)
| = server_handshake_traffic_secret | = server_handshake_traffic_secret
|
v v
0 -> HKDF-Extract Derive-Secret(., "derived secret", "")
| |
v v
Master Secret 0 -> HKDF-Extract = Master Secret
| |
+-----> Derive-Secret(., "client application traffic secret", +-----> Derive-Secret(., "client application traffic secret",
| ClientHello...Server Finished) | ClientHello...Server Finished)
| = client_traffic_secret_0 | = client_traffic_secret_0
| |
+-----> Derive-Secret(., "server application traffic secret", +-----> Derive-Secret(., "server application traffic secret",
| ClientHello...Server Finished) | ClientHello...Server Finished)
| = server_traffic_secret_0 | = server_traffic_secret_0
| |
+-----> Derive-Secret(., "exporter master secret", +-----> Derive-Secret(., "exporter master secret",
| ClientHello...Server Finished) | ClientHello...Server Finished)
| = exporter_secret | = exporter_secret
| |
+-----> Derive-Secret(., "resumption master secret", +-----> Derive-Secret(., "resumption master secret",
ClientHello...Client Finished) ClientHello...Client Finished)
= resumption_secret = resumption_master_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
of the diagram are just raw entropy without context, whereas the of the diagram are just raw entropy without context, whereas the
secrets down the right side include handshake context and therefore secrets down the right side include handshake context and therefore
can be used to derive working keys without additional context. Note can be used to derive working keys without additional context. Note
that the different calls to Derive-Secret may take different Messages that the different calls to Derive-Secret may take different Messages
arguments, even with the same secret. In a 0-RTT exchange, Derive- arguments, even with the same secret. In a 0-RTT exchange, Derive-
Secret is called with four distinct transcripts; in a 1-RTT only Secret is called with four distinct transcripts; in a 1-RTT-only
exchange with three distinct transcripts. exchange with three distinct transcripts.
The complete transcript passed to Derive-Secret is always taken from
the following sequence of handshake messages, starting at the first
ClientHello and including only those messages that were sent:
ClientHello, HelloRetryRequest, ClientHello, ServerHello,
EncryptedExtensions, Server CertificateRequest, Server Certificate,
Server CertificateVerify, Server Finished, EndOfEarlyData, Client
Certificate, Client CertificateVerify, Client Finished.
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 zero bytes is used. Note that this does not
skipping rounds, so if PSK is not in use Early Secret will still be mean skipping rounds, so if PSK is not in use Early Secret will still
HKDF-Extract(0, 0). For the computation of the binder_secret, the be HKDF-Extract(0, 0). For the computation of the binder_secret, the
label is "external psk binder key" for external PSKs and "resumption label is "external psk binder key" for external PSKs (those
psk binder key" for resumption PSKs. The different labels prevents provisioned outside of TLS) and "resumption psk binder key" for
the substitution of one type of PSK for the other. resumption PSKs (those provisioned as the resumption master secret of
a previous handshake). The different labels prevent the substitution
of one type of PSK for the other.
There are multiple potential Early Secret values depending on which There are multiple potential Early Secret values depending on which
PSK the server ultimately selects. The client will need to compute PSK the server ultimately selects. The client will need to compute
one for each potential PSK; if no PSK is selected, it will then need one for each potential PSK; if no PSK is selected, it will then need
to compute the early secret corresponding to the zero PSK. to compute the early secret corresponding to the zero PSK.
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 4.5.3. The next generation of traffic keys is defined in Section 4.6.3. The next generation of traffic keys is
computed by generating client_/server_traffic_secret_N+1 from computed by generating client_/server_traffic_secret_N+1 from
client_/server_traffic_secret_N as described in this section then re- client_/server_traffic_secret_N as described in this section then re-
deriving the traffic keys as 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)
skipping to change at page 79, line 31 skipping to change at page 84, line 43
| | | | | |
| Handshake | [sender]_handshake_traffic_secret | | Handshake | [sender]_handshake_traffic_secret |
| | | | | |
| Application Data | [sender]_traffic_secret_N | | Application Data | [sender]_traffic_secret_N |
+-------------------+-----------------------------------+ +-------------------+-----------------------------------+
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 7.4. (EC)DHE Shared Secret Calculation
A conventional Diffie-Hellman computation is performed. The 7.4.1. Finite Field Diffie-Hellman
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 For finite field groups, a conventional Diffie-Hellman computation is
string is used as the shared secret, and is used in the key schedule performed. The negotiated key (Z) is converted to a byte string by
as specified above. encoding in big-endian and padded with zeros up to the size of the
prime. This byte string is used as the shared secret, and is used in
the key schedule as specified above.
Note that this construction differs from previous versions of TLS Note that this construction differs from previous versions of TLS
which remove leading zeros. which remove leading zeros.
7.3.2. Elliptic Curve Diffie-Hellman 7.4.2. Elliptic Curve Diffie-Hellman
For secp256r1, secp384r1 and secp521r1, ECDH calculations (including For secp256r1, secp384r1 and secp521r1, ECDH calculations (including
parameter and key generation as well as the shared secret parameter and key generation as well as the shared secret
calculation) are performed according to [IEEE1363] using the ECKAS- calculation) are performed according to [IEEE1363] using the ECKAS-
DH1 scheme with the identity map as key derivation function (KDF), so DH1 scheme with the identity map as key derivation function (KDF), so
that the shared secret is the x-coordinate of the ECDH shared secret that the shared secret is the x-coordinate of the ECDH shared secret
elliptic curve point represented as an octet string. Note that this elliptic curve point represented as an octet string. Note that this
octet string (Z in IEEE 1363 terminology) as output by FE2OSP, the octet string (Z in IEEE 1363 terminology) as output by FE2OSP, the
Field Element to Octet String Conversion Primitive, has constant Field Element to Octet String Conversion Primitive, has constant
length for any given field; leading zeros found in this octet string length for any given field; leading zeros found in this octet string
skipping to change at page 80, line 19 skipping to change at page 85, line 33
because TLS does not directly use this secret for anything other than because TLS does not directly use this secret for anything other than
for computing other secrets.) for computing other secrets.)
ECDH functions are used as follows: ECDH functions are used as follows:
- The public key to put into the KeyShareEntry.key_exchange - The public key to put into the KeyShareEntry.key_exchange
structure is the result of applying the ECDH function to the structure is the result of applying the ECDH function to the
secret key of appropriate length (into scalar input) and the secret key of appropriate length (into scalar input) and the
standard public basepoint (into u-coordinate point input). standard public basepoint (into u-coordinate point input).
- The ECDH shared secret is the result of applying ECDH function to - The ECDH shared secret is the result of applying the ECDH function
the secret key (into scalar input) and the peer's public key (into to the secret key (into scalar input) and the peer's public key
u-coordinate point input). The output is used raw, with no (into u-coordinate point input). The output is used raw, with no
processing. processing.
For X25519 and X448, see [RFC7748]. For X25519 and X448, implementations SHOULD use the approach
specified in [RFC7748] to calculate the Diffie-Hellman shared secret.
Implementations MUST check whether the computed Diffie-Hellman shared
secret is the all-zero value and abort if so, as described in
Section 6 of [RFC7748]. If implementers use an alternative
implementation of these elliptic curves, they SHOULD perform the
additional checks specified in Section 7 of [RFC7748].
7.3.3. Exporters 7.5. 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 pseudorandom function (PRF). This document replaces the PRF with
new construction. The exporter interface remains the same. If HKDF, thus requiring a new construction. The exporter interface
context is provided, the value is computed as: remains the same.
HKDF-Expand-Label(Secret, label, context_value, key_length) The exporter value is computed as:
HKDF-Expand-Label(Derive-Secret(Secret, label, ""),
"exporter", Hash(context_value), key_length)
Where Secret is either the early_exporter_secret or the Where Secret is either the early_exporter_secret or the
exporter_secret. Implementations MUST use the exporter_secret unless exporter_secret. Implementations MUST use the exporter_secret unless
explicitly specified by the application. When adding TLS 1.3 to TLS explicitly specified by the application. A separate interface for
1.2 stacks, the exporter_secret MUST be for the existing exporter the early exporter is RECOMMENDED, especially on a server where a
interface. single interface can make the early exporter inaccessible.
If no context is provided, the value is computed as:
HKDF-Expand-Label(Secret, label, "", key_length) If no context is provided, the context_value is zero-length.
Consequently, providing no context computes the same value as
providing an empty context. This is a change from previous versions
of TLS where an empty context produced a different output to an
absent context. As of this document's publication, no allocated
exporter label is used both with and without a context. Future
specifications MUST NOT define a use of exporters that permit both an
empty context and no context with the same label. New uses of
exporters SHOULD provide a context in all exporter computations,
though the value could be empty.
Note that providing no context computes the same value as providing Requirements for the format of exporter labels are defined in section
an empty context. As of this document's publication, no allocated 4 of [RFC5705].
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. Mandatory-to-Implement 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. (see Appendix A.4) suites. (see Appendix B.4)
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
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. Mandatory-to-Implement 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:
- Supported Versions ("supported_versions"; Section 4.2.1) - Supported Versions ("supported_versions"; Section 4.2.1)
- Cookie ("cookie"; Section 4.2.2) - Cookie ("cookie"; Section 4.2.2)
- Signature Algorithms ("signature_algorithms"; Section 4.2.3) - Signature Algorithms ("signature_algorithms"; Section 4.2.3)
- Negotiated Groups ("supported_groups"; Section 4.2.4) - Negotiated Groups ("supported_groups"; Section 4.2.4)
- Key Share ("key_share"; 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])
All implementations MUST send and use these extensions when offering All implementations MUST send and use these extensions when offering
applicable features: applicable features:
- "supported_versions" is REQUIRED for all ClientHello messages. - "supported_versions" is REQUIRED for all ClientHello messages.
- "signature_algorithms" is REQUIRED for certificate authentication. - "signature_algorithms" is REQUIRED for certificate authentication.
- "supported_groups" and "key_share" are REQUIRED for DHE or ECDHE - "supported_groups" and "key_share" are REQUIRED for DHE or ECDHE
skipping to change at page 82, line 15 skipping to change at page 87, line 36
A client is considered to be attempting to negotiate using this A client is considered to be attempting to negotiate using this
specification if the ClientHello contains a "supported_versions" specification if the ClientHello contains a "supported_versions"
extension with a version indicating TLS 1.3. Such a ClientHello extension with a version indicating TLS 1.3. Such a ClientHello
message MUST meet the following requirements: message MUST meet the following requirements:
- If not containing a "pre_shared_key" extension, it MUST contain - If not containing a "pre_shared_key" extension, it MUST contain
both a "signature_algorithms" extension and a "supported_groups" both a "signature_algorithms" extension and a "supported_groups"
extension. extension.
- If containing a "supported_groups" extension, it MUST also contain - If containing a "supported_groups" extension, it MUST also contain
a "key_share" extension, and vice versa. (an empty a "key_share" extension, and vice versa. An empty
KeyShare.client_shares vector is permitted) KeyShare.client_shares vector is permitted.
Servers receiving a ClientHello which does not conform to these Servers receiving a ClientHello which does not conform to these
requirements MUST abort the handshake with a "missing_extension" requirements MUST abort the handshake with a "missing_extension"
alert. alert.
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 by terminating the connection with lacking a "server_name" extension by terminating the connection with
a "missing_extension" alert. a "missing_extension" alert.
9. Security Considerations 9. Security Considerations
Security issues are discussed throughout this memo, especially in Security issues are discussed throughout this memo, especially in
Appendix B, Appendix C, and Appendix D. Appendix C, Appendix D, and Appendix E.
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 [RFC5226]. 0-254 (decimal) are assigned via Specification Required [RFC5226].
Values with the first byte 255 (decimal) are reserved for Private Values with the first byte 255 (decimal) are reserved for Private
Use [RFC5226]. Use [RFC5226].
IANA [SHALL add/has added] the cipher suites listed in IANA [SHALL add/has added] the cipher suites listed in
Appendix A.4 to the registry. The "Value" and "Description" Appendix B.4 to the registry. The "Value" and "Description"
columns are taken from the table. The "DTLS-OK" and "Recommended" columns are taken from the table. The "DTLS-OK" and "Recommended"
columns are both marked as "Yes" for each new cipher suite. columns are both marked as "Yes" for each new cipher suite.
[[This assumes [I-D.sandj-tls-iana-registry-updates] has been [[This assumes [I-D.ietf-tls-iana-registry-updates] has been
applied.]] applied.]]
- TLS ContentType Registry: Future values are allocated via - TLS ContentType Registry: Future values are allocated via
Standards Action [RFC5226]. Standards Action [RFC5226].
- TLS Alert Registry: Future values are allocated via Standards - TLS Alert Registry: Future values are allocated via Standards
Action [RFC5226]. IANA [SHALL update/has updated] this registry Action [RFC5226]. IANA [SHALL update/has updated] this registry
to include values for "end_of_early_data" and "missing_extension". to include values for "missing_extension" and
"certificate_required".
- TLS HandshakeType Registry: Future values are allocated via - TLS HandshakeType Registry: Future values are allocated via
Standards Action [RFC5226]. IANA [SHALL update/has updated] this Standards Action [RFC5226]. IANA [SHALL update/has updated] this
registry to rename item 4 from "NewSessionTicket" to registry to rename item 4 from "NewSessionTicket" to
"new_session_ticket" and to add the "hello_retry_request", "new_session_ticket" and to add the "hello_retry_request",
"encrypted_extensions", and "key_update" values. "encrypted_extensions", "end_of_early_data", "key_update", and
"handshake_hash" values.
This document also uses a registry originally created in [RFC4366]. This document also uses a registry originally created in [RFC4366].
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 - IANA [SHALL update/has updated] this registry to include the
range 0-254 (decimal) are assigned via Specification Required "key_share", "pre_shared_key", "psk_key_exchange_modes",
[RFC5226]. Values with the first byte 255 (decimal) are reserved "early_data", "cookie", "supported_versions",
for Private Use [RFC5226]. IANA [SHALL update/has updated] this "certificate_authorities", and "oid_filters" extensions with the
registry to include the "key_share", "pre_shared_key", and values defined in this document and the Recommended value of
"early_data" extensions as defined in this document. "Yes".
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
1.3" column with the following six values: "Client", indicating
that the server shall not send them. "Clear", indicating that
they shall be in the ServerHello. "Encrypted", indicating that
they shall be in the EncryptedExtensions block, "Certificate"
indicating that they shall be in the Certificate block, "Ticket"
indicating that they can appear in the NewSessionTicket message
(only) and "No" indicating that they are not used in TLS 1.3.
This column [shall be/has been] initially populated with the
values in this document.
IANA [shall update/has updated] this registry to include a
"HelloRetryRequest" column with the following two values: "Yes",
indicating it may be sent in HelloRetryRequest, and "No",
indicating it may not be sent in HelloRetryRequest. This column
[shall be/has been] initially populated with the values in this
document.
+-----------------------------+----------+----------+---------------+
| Extension | Recommen | TLS 1.3 | HelloRetryReq |
| | ded | | uest |
+-----------------------------+----------+----------+---------------+
| server_name [RFC6066] | Yes | Encrypte | No |
| | | d | |
| | | | |
| max_fragment_length | Yes | Encrypte | No |
| [RFC6066] | | d | |
| | | | |
| client_certificate_url | Yes | Encrypte | No |
| [RFC6066] | | d | |
| | | | |
| trusted_ca_keys [RFC6066] | Yes | Encrypte | No |
| | | d | |
| | | | |
| truncated_hmac [RFC6066] | Yes | No | No |
| | | | |
| status_request [RFC6066] | Yes | Certific | No |
| | | ate | |
| | | | |
| user_mapping [RFC4681] | Yes | Encrypte | No |
| | | d | |
| | | | |
| client_authz [RFC5878] | No | No | No |
| | | | |
| server_authz [RFC5878] | No | No | No |
| | | | |
| cert_type [RFC6091] | Yes | Encrypte | No |
| | | d | |
| | | | |
| supported_groups [RFC7919] | Yes | Encrypte | No |
| | | d | |
| | | | |
| ec_point_formats [RFC4492] | Yes | No | No |
| | | | |
| srp [RFC5054] | No | No | No |
| | | | |
| signature_algorithms | Yes | Client | No |
| [RFC5246] | | | |
| | | | |
| use_srtp [RFC5764] | Yes | Encrypte | No |
| | | d | |
| | | | |
| heartbeat [RFC6520] | Yes | Encrypte | No |
| | | d | |
| | | | |
| application_layer_protocol_ | Yes | Encrypte | No |
| negotiation [RFC7301] | | d | |
| | | | |
| status_request_v2 [RFC6961] | Yes | Certific | No |
| | | ate | |
| | | | |
| signed_certificate_timestam | No | Certific | No |
| p [RFC6962] | | ate | |
| | | | |
| client_certificate_type | Yes | Encrypte | No |
| [RFC7250] | | d | |
| | | | |
| server_certificate_type | Yes | Certific | No |
| [RFC7250] | | ate | |
| | | | |
| padding [RFC7685] | Yes | Client | No |
| | | | |
| encrypt_then_mac [RFC7366] | Yes | No | No |
| | | | |
| extended_master_secret | Yes | No | No |
| [RFC7627] | | | |
| | | | |
| SessionTicket TLS [RFC4507] | Yes | No | No |
| | | | |
| renegotiation_info | Yes | No | No |
| [RFC5746] | | | |
| | | | |
| key_share [[this document]] | Yes | Clear | Yes |
| | | | |
| pre_shared_key [[this | Yes | Clear | No |
| document]] | | | |
| | | | |
| psk_key_exchange_modes | Yes | Client | No |
| [[this document]] | | | |
| | | | |
| early_data [[this | Yes | Encrypte | No |
| document]] | | d | |
| | | | |
| cookie [[this document]] | Yes | Client | Yes |
| | | | |
| supported_versions [[this | Yes | Client | No |
| document]] | | | |
| | | | |
| ticket_early_data_info | Yes | Ticket | No |
| [[this document]] | | | |
+-----------------------------+----------+----------+---------------+
IANA [SHALL update/has updated] this registry to include the values - IANA [SHALL update/has updated] this registry to include a "TLS
listed above that correspond to this document. 1.3" column which lists the messages in which the extension may
appear. This column [SHALL be/has been] initially populated from
the table in Section 4.2 with any extension not listed there
marked as "-" to indicate that it is not used by TLS 1.3.
In addition, this document defines two new registries to be In addition, this document defines a new registry to be maintained by
maintained by IANA 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
[RFC5226]. Values with the first byte 255 (decimal) are reserved [RFC5226]. Values with the first byte 255 (decimal) are reserved
for Private Use [RFC5226]. Values with the first byte in the for Private Use [RFC5226]. Values with the first byte in the
range 0-6 or with the second byte in the range 0-3 that are not range 0-6 or with the second byte in the range 0-3 that are not
currently allocated are reserved for backwards compatibility. currently allocated are reserved for backwards compatibility.
This registry SHALL have a "Recommended" column. The registry This registry SHALL have a "Recommended" column. The registry
[shall be/ has been] initially populated with the values described [shall be/ has been] initially populated with the values described
in Section 4.2.3. The following values SHALL be marked as in Section 4.2.3. The following values SHALL be marked as
"Recommended": ecdsa_secp256r1_sha256, ecdsa_secp384r1_sha384, "Recommended": ecdsa_secp256r1_sha256, ecdsa_secp384r1_sha384,
rsa_pss_sha256, rsa_pss_sha384, rsa_pss_sha512, ed25519. rsa_pss_sha256, rsa_pss_sha384, rsa_pss_sha512, ed25519.
Finally, this document obsoletes the TLS HashAlgorithm Registry and Finally, this document obsoletes the TLS HashAlgorithm Registry and
the TLS SignatureAlgorithm Registry, both originally created in the TLS SignatureAlgorithm Registry, both originally created in
[RFC5246]. IANA [SHALL update/has updated] the TLS HashAlgorithm [RFC5246]. IANA [SHALL update/has updated] the TLS HashAlgorithm
Registry to list values 7-223 as "Reserved" and the TLS Registry to list values 7-223 as "Reserved" and the TLS
SignatureAlgorithm Registry to list values 4-233 as "Reserved". SignatureAlgorithm Registry to list values 4-223 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]
Josefsson, S. and I. Liusvaara, "Edwards-curve Digital
Signature Algorithm (EdDSA)", draft-irtf-cfrg-eddsa-08
(work in progress), August 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 88, line 5 skipping to change at page 91, line 5
[RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate [RFC6962] Laurie, B., Langley, A., and E. Kasper, "Certificate
Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013, Transparency", RFC 6962, DOI 10.17487/RFC6962, June 2013,
<http://www.rfc-editor.org/info/rfc6962>. <http://www.rfc-editor.org/info/rfc6962>.
[RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature [RFC6979] Pornin, T., "Deterministic Usage of the Digital Signature
Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature
Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August
2013, <http://www.rfc-editor.org/info/rfc6979>. 2013, <http://www.rfc-editor.org/info/rfc6979>.
[RFC7507] Moeller, B. and A. Langley, "TLS Fallback Signaling Cipher
Suite Value (SCSV) for Preventing Protocol Downgrade
Attacks", RFC 7507, DOI 10.17487/RFC7507, April 2015,
<http://www.rfc-editor.org/info/rfc7507>.
[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF [RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015, Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<http://www.rfc-editor.org/info/rfc7539>. <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>.
[RFC7919] Gillmor, D., "Negotiated Finite Field Diffie-Hellman [RFC7919] Gillmor, D., "Negotiated Finite Field Diffie-Hellman
Ephemeral Parameters for Transport Layer Security (TLS)", Ephemeral Parameters for Transport Layer Security (TLS)",
RFC 7919, DOI 10.17487/RFC7919, August 2016, RFC 7919, DOI 10.17487/RFC7919, August 2016,
<http://www.rfc-editor.org/info/rfc7919>. <http://www.rfc-editor.org/info/rfc7919>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<http://www.rfc-editor.org/info/rfc8032>.
[SHS] National Institute of Standards and Technology, U.S. [SHS] National Institute of Standards and Technology, U.S.
Department of Commerce, "Secure Hash Standard", NIST FIPS Department of Commerce, "Secure Hash Standard", NIST FIPS
PUB 180-4, March 2012. PUB 180-4, March 2012.
[X690] ITU-T, "Information technology - ASN.1 encoding Rules: [X690] ITU-T, "Information technology - ASN.1 encoding Rules:
Specification of Basic Encoding Rules (BER), Canonical Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ISO/IEC 8825-1:2002, 2002. (DER)", ISO/IEC 8825-1:2002, 2002.
[X962] ANSI, "Public Key Cryptography For The Financial Services [X962] ANSI, "Public Key Cryptography For The Financial Services
skipping to change at page 88, line 44 skipping to change at page 92, line 5
Luykx, A. and K. Paterson, "Limits on Authenticated Luykx, A. and K. Paterson, "Limits on Authenticated
Encryption Use in TLS", 2016, Encryption Use in TLS", 2016,
<http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>. <http://www.isg.rhul.ac.uk/~kp/TLS-AEbounds.pdf>.
[BBFKZG16] [BBFKZG16]
Bhargavan, K., Brzuska, C., Fournet, C., Kohlweiss, M., Bhargavan, K., Brzuska, C., Fournet, C., Kohlweiss, M.,
Zanella-Beguelin, S., and M. Green, "Downgrade Resilience Zanella-Beguelin, S., and M. Green, "Downgrade Resilience
in Key-Exchange Protocols", Proceedings of IEEE Symposium in Key-Exchange Protocols", Proceedings of IEEE Symposium
on Security and Privacy (Oakland) 2016 , 2016. on Security and Privacy (Oakland) 2016 , 2016.
[CCG16] Cohn-Gordon, K., Cremers, C., and L. Garratt, "On Post-
Compromise Security", IEEE Computer Security Foundations
Symposium , 2015.
[CHHSV17] Cremers, C., Horvat, M., Hoyland, J., van der Merwe, T.,
and S. Scott, "Awkward Handshake: Possible mismatch of
client/server view on client authentication in post-
handshake mode in Revision 18", 2017,
<https://www.ietf.org/mail-archive/web/tls/current/
msg22382.html>.
[CHSV16] Cremers, C., Horvat, M., Scott, S., and T. van der Merwe, [CHSV16] Cremers, C., Horvat, M., Scott, S., and T. van der Merwe,
"Automated Analysis and Verification of TLS 1.3: 0-RTT, "Automated Analysis and Verification of TLS 1.3: 0-RTT,
Resumption and Delayed Authentication", Proceedings of Resumption and Delayed Authentication", Proceedings of
IEEE Symposium on Security and Privacy (Oakland) 2016 , IEEE Symposium on Security and Privacy (Oakland) 2016 ,
2016. 2016.
[CK01] Canetti, R. and H. Krawczyk, "Analysis of Key-Exchange [CK01] Canetti, R. and H. Krawczyk, "Analysis of Key-Exchange
Protocols and Their Use for Building Secure Channels", Protocols and Their Use for Building Secure Channels",
Proceedings of Eurocrypt 2001 , 2001. Proceedings of Eurocrypt 2001 , 2001.
[DOW92] Diffie, W., van Oorschot, P., and M. Wiener, [DOW92] Diffie, W., van Oorschot, P., and M. Wiener,
""Authentication and authenticated key exchanges"", ""Authentication and authenticated key exchanges"",
Designs, Codes and Cryptography , n.d.. Designs, Codes and Cryptography , 1992.
[DSS] National Institute of Standards and Technology, U.S. [DSS] National Institute of Standards and Technology, U.S.
Department of Commerce, "Digital Signature Standard, Department of Commerce, "Digital Signature Standard,
version 4", NIST FIPS PUB 186-4, 2013. version 4", NIST FIPS PUB 186-4, 2013.
[ECDSA] American National Standards Institute, "Public Key [ECDSA] American National Standards Institute, "Public Key
Cryptography for the Financial Services Industry: The Cryptography for the Financial Services Industry: The
Elliptic Curve Digital Signature Algorithm (ECDSA)", Elliptic Curve Digital Signature Algorithm (ECDSA)",
ANSI ANS X9.62-2005, November 2005. ANSI ANS X9.62-2005, November 2005.
[FGSW16] Fischlin, M., Guenther, F., Schmidt, B., and B. Warinschi, [FGSW16] Fischlin, M., Guenther, F., Schmidt, B., and B. Warinschi,
"Key Confirmation in Key Exchange: A Formal Treatment and "Key Confirmation in Key Exchange: A Formal Treatment and
Implications for TLS 1.3", Proceedings of IEEE Symposium Implications for TLS 1.3", Proceedings of IEEE Symposium
on Security and Privacy (Oakland) 2016 , 2016. on Security and Privacy (Oakland) 2016 , 2016.
[FI06] Finney, H., "Bleichenbacher's RSA signature forgery based
on implementation error", August 2006,
<https://www.ietf.org/mail-archive/web/openpgp/current/
msg00999.html>.
[FW15] Florian Weimer, ., "Factoring RSA Keys With TLS Perfect [FW15] Florian Weimer, ., "Factoring RSA Keys With TLS Perfect
Forward Secrecy", September 2015. Forward Secrecy", September 2015.
[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.sandj-tls-iana-registry-updates] [HGFS15] Hlauschek, C., Gruber, M., Fankhauser, F., and C. Schanes,
"Prying Open Pandora's Box: KCI Attacks against TLS",
Proceedings of USENIX Workshop on Offensive Technologies ,
2015.
[I-D.ietf-tls-iana-registry-updates]
Salowey, J. and S. Turner, "D/TLS IANA Registry Updates", Salowey, J. and S. Turner, "D/TLS IANA Registry Updates",
draft-sandj-tls-iana-registry-updates-01 (work in draft-ietf-tls-iana-registry-updates-00 (work in
progress), October 2016. progress), January 2017.
[I-D.ietf-tls-tls13-vectors]
Thomson, M., "Example Handshake Traces for TLS 1.3",
draft-ietf-tls-tls13-vectors-00 (work in progress),
January 2017.
[IEEE1363] [IEEE1363]
IEEE, "Standard Specifications for Public Key IEEE, "Standard Specifications for Public Key
Cryptography", IEEE 1363 , 2000. Cryptography", IEEE 1363 , 2000.
[KEYAGREEMENT]
Barker, E., Lily Chen, ., Roginsky, A., and M. Smid,
"Recommendation for Pair-Wise Key Establishment Schemes
Using Discrete Logarithm Cryptography", NIST Special
Publication 800-38D, May 2013.
[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.
[PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate [PKCS6] RSA Laboratories, "PKCS #6: RSA Extended Certificate
Syntax Standard, version 1.5", November 1993. Syntax Standard, version 1.5", November 1993.
[PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message [PKCS7] RSA Laboratories, "PKCS #7: RSA Cryptographic Message
Syntax Standard, version 1.5", November 1993. Syntax Standard, version 1.5", November 1993.
[PSK-FINISHED] [PSK-FINISHED]
Cremers, C., Horvat, M., van der Merwe, T., and S. Scott, Cremers, C., Horvat, M., van der Merwe, T., and S. Scott,
"Revision 10: possible attack if client authentication is "Revision 10: possible attack if client authentication is
allowed during PSK", 2015, <https://www.ietf.org/mail- allowed during PSK", 2015, <https://www.ietf.org/mail-
archive/web/tls/current/msg18215.html>. archive/web/tls/current/msg18215.html>.
[RECORD] Bhargavan, K., Delignat-Lavaud, A., Fournet, C.,
Kohlweiss, M., Pan, J., Protzenko, J., Rastogi, A., Swamy,
N., Zanella-Beguelin, S., and J. Zinzindohoue,
"Implementing and Proving the TLS 1.3 Record Layer",
December 2016, <http://eprint.iacr.org/2016/1178>.
[REKEY] Abdalla, M. and M. Bellare, "Increasing the Lifetime of a
Key: A Comparative Analysis of the Security of Re-keying
Techniques", ASIACRYPT2000 , October 2000.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, DOI 10.17487/RFC3552, July 2003,
<http://www.rfc-editor.org/info/rfc3552>. <http://www.rfc-editor.org/info/rfc3552>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086, "Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005, DOI 10.17487/RFC4086, June 2005,
<http://www.rfc-editor.org/info/rfc4086>. <http://www.rfc-editor.org/info/rfc4086>.
skipping to change at page 94, line 5 skipping to change at page 98, line 5
[TIMING] Boneh, D. and D. Brumley, "Remote timing attacks are [TIMING] Boneh, D. and D. Brumley, "Remote timing attacks are
practical", USENIX Security Symposium, 2003. practical", USENIX Security Symposium, 2003.
[X501] "Information Technology - Open Systems Interconnection - [X501] "Information Technology - Open Systems Interconnection -
The Directory: Models", ITU-T X.501, 1993. The Directory: Models", ITU-T X.501, 1993.
11.3. URIs 11.3. URIs
[1] mailto:tls@ietf.org [1] mailto:tls@ietf.org
Appendix A. Protocol Data Structures and Constant Values Appendix A. State Machine
This section provides a summary of the legal state transitions for
the client and server handshakes. State names (in all capitals,
e.g., START) have no formal meaning but are provided for ease of
comprehension. Messages which are sent only sometimes are indicated
in [].
A.1. Client
START <----+
Send ClientHello | | Recv HelloRetryRequest
/ v |
| WAIT_SH ---+
Can | | Recv ServerHello
send | V
early | WAIT_EE
data | | Recv EncryptedExtensions
| +--------+--------+
| Using | | Using certificate
| PSK | v
| | WAIT_CERT_CR
| | Recv | | Recv CertificateRequest
| | Certificate | v
| | | WAIT_CERT
| | | | Recv Certificate
| | v v
| | WAIT_CV
| | | Recv CertificateVerify
| +> WAIT_FINISHED <+
| | Recv Finished
\ |
| [Send EndOfEarlyData]
| [Send Certificate [+ CertificateVerify]]
| Send Finished
Can send v
app data --> CONNECTED
after
here
A.2. Server
START <-----+
Recv ClientHello | | Send HelloRetryRequest
v |
RECVD_CH ----+
| Select parameters
v
NEGOTIATED
| Send ServerHello
| Send EncryptedExtensions
| [Send CertificateRequest]
Can send | [Send Certificate + CertificateVerify]
app data --> | Send Finished
after +--------+--------+
here No 0-RTT | | 0-RTT
| v
| WAIT_EOED <---+
| Recv | | | Recv
| EndOfEarlyData | | | early data
| | +-----+
+> WAIT_FLIGHT2 <-+
|
+--------+--------+
No auth | | Client auth
| |
| v
| WAIT_CERT
| Recv | | Recv Certificate
| empty | v
| Certificate | WAIT_CV
| | | Recv
| v | CertificateVerify
+-> WAIT_FINISHED <---+
| Recv Finished
v
CONNECTED
Appendix B. Protocol Data Structures and Constant Values
This section describes protocol types and constants. Values listed This section describes protocol types and constants. Values listed
as _RESERVED were used in previous versions of TLS and are listed as _RESERVED were used in previous versions of TLS and are listed
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 B.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 = 0x0301; /* TLS v1.x */ ProtocolVersion legacy_record_version;
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 = 23; /* application_data */ ContentType opaque_type = 23; /* application_data */
ProtocolVersion legacy_record_version = 0x0301; /* TLS v1.x */ ProtocolVersion legacy_record_version = 0x0301; /* TLS v1.x */
uint16 length; uint16 length;
opaque encrypted_record[length]; opaque encrypted_record[length];
} TLSCiphertext; } TLSCiphertext;
A.2. Alert Messages B.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),
end_of_early_data(1),
unexpected_message(10), unexpected_message(10),
bad_record_mac(20), bad_record_mac(20),
decryption_failed_RESERVED(21), decryption_failed_RESERVED(21),
record_overflow(22), record_overflow(22),
decompression_failure_RESERVED(30), decompression_failure_RESERVED(30),
handshake_failure(40), handshake_failure(40),
no_certificate_RESERVED(41), no_certificate_RESERVED(41),
bad_certificate(42), bad_certificate(42),
unsupported_certificate(43), unsupported_certificate(43),
certificate_revoked(44), certificate_revoked(44),
skipping to change at page 96, line 5 skipping to change at page 102, line 5
unknown_psk_identity(115), unknown_psk_identity(115),
certificate_required(116), certificate_required(116),
(255) (255)
} AlertDescription; } AlertDescription;
struct { struct {
AlertLevel level; AlertLevel level;
AlertDescription description; AlertDescription description;
} Alert; } Alert;
A.3. Handshake Protocol B.3. Handshake Protocol
enum { enum {
hello_request_RESERVED(0), hello_request_RESERVED(0),
client_hello(1), client_hello(1),
server_hello(2), server_hello(2),
hello_verify_request_RESERVED(3),
new_session_ticket(4), new_session_ticket(4),
end_of_early_data(5),
hello_retry_request(6), hello_retry_request(6),
encrypted_extensions(8), encrypted_extensions(8),
certificate(11), certificate(11),
server_key_exchange_RESERVED(12), server_key_exchange_RESERVED(12),
certificate_request(13), certificate_request(13),
server_hello_done_RESERVED(14), server_hello_done_RESERVED(14),
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),
message_hash(254),
(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 (Handshake.msg_type) { select (Handshake.msg_type) {
case client_hello: ClientHello; case client_hello: ClientHello;
case server_hello: ServerHello; case server_hello: ServerHello;
case end_of_early_data: EndOfEarlyData;
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 B.3.1. Key Exchange Messages
uint16 ProtocolVersion; uint16 ProtocolVersion;
opaque Random[32]; opaque Random[32];
uint8 CipherSuite[2]; /* Cryptographic suite selector */ uint8 CipherSuite[2]; /* Cryptographic suite selector */
struct { struct {
ProtocolVersion legacy_version = 0x0303; /* TLS v1.2 */ ProtocolVersion legacy_version = 0x0303; /* 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<8..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<6..2^16-1>;
} ServerHello; } ServerHello;
struct { struct {
ProtocolVersion server_version; ProtocolVersion server_version;
CipherSuite cipher_suite;
Extension extensions<2..2^16-1>; Extension extensions<2..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),
supported_versions(43), supported_versions(43),
cookie(44), cookie(44),
psk_key_exchange_modes(45), psk_key_exchange_modes(45),
ticket_early_data_info(46), certificate_authorities(47),
oid_filters(48),
(65535) (65535)
} ExtensionType; } 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 (Handshake.msg_type) { select (Handshake.msg_type) {
skipping to change at page 98, line 10 skipping to change at page 104, line 15
KeyShareEntry client_shares<0..2^16-1>; KeyShareEntry client_shares<0..2^16-1>;
case hello_retry_request: case hello_retry_request:
NamedGroup selected_group; NamedGroup selected_group;
case server_hello: case server_hello:
KeyShareEntry server_share; KeyShareEntry server_share;
}; };
} KeyShare; } KeyShare;
enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeMode;
struct { struct {
opaque identity<0..2^16-1>; PskKeyExchangeMode ke_modes<1..255>;
} PskKeyExchangeModes;
struct {} Empty;
struct {
select (Handshake.msg_type) {
case new_session_ticket: uint32 max_early_data_size;
case client_hello: Empty;
case encrypted_extensions: Empty;
};
} EarlyDataIndication;
struct {
opaque identity<1..2^16-1>;
uint32 obfuscated_ticket_age; uint32 obfuscated_ticket_age;
} PskIdentity; } PskIdentity;
opaque PskBinderEntry<32..255>; opaque PskBinderEntry<32..255>;
struct { struct {
select (Handshake.msg_type) { select (Handshake.msg_type) {
case client_hello: case client_hello:
PskIdentity identities<6..2^16-1>; PskIdentity identities<7..2^16-1>;
PskBinderEntry binders<33..2^16-1>; PskBinderEntry binders<33..2^16-1>;
case server_hello: case server_hello:
uint16 selected_identity; uint16 selected_identity;
}; };
} PreSharedKeyExtension; } PreSharedKeyExtension;
enum { psk_ke(0), psk_dhe_ke(1), (255) } PskKeyExchangeMode; B.3.1.1. Version Extension
struct {
PskKeyExchangeMode ke_modes<1..255>;
} PskKeyExchangeModes;
struct {
} EarlyDataIndication;
A.3.1.1. Version Extension
struct { struct {
ProtocolVersion versions<2..254>; ProtocolVersion versions<2..254>;
} SupportedVersions; } SupportedVersions;
A.3.1.2. Cookie Extension B.3.1.2. Cookie Extension
struct { struct {
opaque cookie<1..2^16-1>; opaque cookie<1..2^16-1>;
} Cookie; } Cookie;
A.3.1.3. Signature Algorithm Extension B.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 (0x0804), rsa_pss_sha256(0x0804),
rsa_pss_sha384 (0x0805), rsa_pss_sha384(0x0805),
rsa_pss_sha512 (0x0806), rsa_pss_sha512(0x0806),
/* EdDSA algorithms */ /* EdDSA algorithms */
ed25519 (0x0807), ed25519(0x0807),
ed448 (0x0808), 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;
struct { struct {
SignatureScheme supported_signature_algorithms<2..2^16-2>; SignatureScheme supported_signature_algorithms<2..2^16-2>;
} SignatureSchemeList; } SignatureSchemeList;
A.3.1.4. Supported Groups Extension B.3.1.4. Supported Groups Extension
enum { enum {
/* Elliptic Curve Groups (ECDHE) */ /* Elliptic Curve Groups (ECDHE) */
obsolete_RESERVED (1..22), obsolete_RESERVED(0x0001..0x0016),
secp256r1 (23), secp384r1 (24), secp521r1 (25), secp256r1(0x0017), secp384r1(0x0018), secp521r1(0x0019),
obsolete_RESERVED (26..28), obsolete_RESERVED(0x001A..0x001C),
x25519 (29), x448 (30), x25519(0x001D), x448(0x001E),
/* Finite Field Groups (DHE) */ /* Finite Field Groups (DHE) */
ffdhe2048 (256), ffdhe3072 (257), ffdhe4096 (258), ffdhe2048(0x0100), ffdhe3072(0x0101), ffdhe4096 (0x0102),
ffdhe6144 (259), ffdhe8192 (260), ffdhe6144(0x0103), ffdhe8192(0x0104),
/* 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<2..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.3.2. Server Parameters Messages B.3.2. Server Parameters Messages
opaque DistinguishedName<1..2^16-1>;
struct {
DistinguishedName authorities<3..2^16-1>;
} CertificateAuthoritiesExtension;
struct { struct {
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} EncryptedExtensions; } EncryptedExtensions;
opaque DistinguishedName<1..2^16-1>; struct {
opaque certificate_request_context<0..2^8-1>;
Extension extensions<2..2^16-1>;
} CertificateRequest;
struct { struct {
opaque certificate_extension_oid<1..2^8-1>; opaque certificate_extension_oid<1..2^8-1>;
opaque certificate_extension_values<0..2^16-1>; opaque certificate_extension_values<0..2^16-1>;
} CertificateExtension; } OIDFilter;
struct { struct {
opaque certificate_request_context<0..2^8-1>; OIDFilter filters<0..2^16-1>;
SignatureScheme } OIDFilterExtension;
supported_signature_algorithms<2..2^16-2>;
DistinguishedName certificate_authorities<0..2^16-1>;
CertificateExtension certificate_extensions<0..2^16-1>;
} CertificateRequest;
A.3.3. Authentication Messages B.3.3. Authentication Messages
opaque ASN1Cert<1..2^24-1>; opaque ASN1Cert<1..2^24-1>;
struct { struct {
ASN1Cert cert_data; ASN1Cert cert_data;
Extension extensions<0..2^16-1>; Extension extensions<0..2^16-1>;
} CertificateEntry; } CertificateEntry;
struct { struct {
opaque certificate_request_context<0..2^8-1>; opaque certificate_request_context<0..2^8-1>;
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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 B.3.4. Ticket Establishment
struct { struct {
uint32 ticket_lifetime; uint32 ticket_lifetime;
uint32 ticket_age_add; uint32 ticket_age_add;
opaque ticket<1..2^16-1>; opaque ticket<1..2^16-1>;
Extension extensions<0..2^16-2>; Extension extensions<0..2^16-2>;
} NewSessionTicket; } NewSessionTicket;
struct { B.3.5. Updating Keys
uint32 max_early_data_size;
} TicketEarlyDataInfo;
A.3.5. Updating Keys struct {} EndOfEarlyData;
enum { enum {
update_not_requested(0), update_requested(1), (255) update_not_requested(0), update_requested(1), (255)
} KeyUpdateRequest; } KeyUpdateRequest;
struct { struct {
KeyUpdateRequest request_update; KeyUpdateRequest request_update;
} KeyUpdate; } KeyUpdate;
A.4. Cipher Suites B.4. Cipher Suites
A symmetric cipher suite defines the pair of the AEAD algorithm and A symmetric cipher suite defines the pair of the AEAD algorithm and
hash algorithm to be used with HKDF. Cipher suite names follow the hash algorithm to be used with HKDF. Cipher suite names follow the
naming convention: naming convention:
CipherSuite TLS_AEAD_HASH = VALUE; CipherSuite TLS_AEAD_HASH = VALUE;
+-----------+------------------------------------------------+ +-----------+------------------------------------------------+
| Component | Contents | | Component | Contents |
+-----------+------------------------------------------------+ +-----------+------------------------------------------------+
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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 be used for TLS 1.2. specifying the symmetric ciphers, and cannot 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.
Appendix B. Implementation Notes Appendix C. 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.
[I-D.ietf-tls-tls13-vectors] provides test vectors for TLS 1.3
handshakes.
B.1. API considerations for 0-RTT C.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 C.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 preferable 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 C.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
signing by a trusted Certificate Authority (CA). The selection and signing by a trusted Certificate Authority (CA). The selection and
addition of trusted CAs should be done very carefully. Users should addition of trust anchors should be done very carefully. Users
be able to view information about the certificate and root CA. should be able to view information about the certificate and trust
Applications SHOULD also enforce minimum and maximum key sizes. For anchor. Applications SHOULD also enforce minimum and maximum key
example, certification paths containing keys or signatures weaker sizes. For example, certification paths containing keys or
than 2048-bit RSA or 224-bit ECDSA are not appropriate for secure signatures weaker than 2048-bit RSA or 224-bit ECDSA are not
applications. appropriate for secure applications.
B.4. Implementation Pitfalls C.4. Implementation Pitfalls
Implementation experience has shown that certain parts of earlier TLS Implementation experience has shown that certain parts of earlier TLS
specifications are not easy to understand, and have been a source of specifications are not easy to understand, and have been a source of
interoperability and security problems. Many of these areas have interoperability and security problems. Many of these areas have
been clarified in this document, but this appendix contains a short been clarified in this document, but this appendix contains a short
list of the most important things that require special attention from list of the most important things that require special attention from
implementors. implementors.
TLS protocol issues: TLS protocol issues:
- Do you correctly handle handshake messages that are fragmented to - Do you correctly handle handshake messages that are fragmented to
multiple TLS records (see Section 5.1)? Including corner cases multiple TLS records (see Section 5.1)? Including corner cases
like a ClientHello that is split to several small fragments? Do like a ClientHello that is split to several small fragments? Do
you fragment handshake messages that exceed the maximum fragment you fragment handshake messages that exceed the maximum fragment
size? In particular, the certificate and certificate request size? In particular, the Certificate and CertificateRequest
handshake messages can be large enough to require fragmentation. handshake messages can be large enough to require fragmentation.
- Do you ignore the TLS record layer version number in all TLS - Do you ignore the TLS record layer version number in all
records? (see Appendix C) unencrypted TLS records? (see Appendix D)
- 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_algorithms" extension) is completely and MD5 (via the "signature_algorithms" 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 D)
- Do you handle TLS extensions in ClientHello correctly, including - Do you handle TLS extensions in ClientHello correctly, including
unknown extensions. 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 4.4.1.3)? Section 4.4.2.3)?
- 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?
- 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 4.2.4), and hello extensions (Section 4.2), named groups (Section 4.2.4), and
signature algorithms (Section 4.2.3)? signature algorithms (Section 4.2.3)?
- As a server, do you send a HelloRetryRequest to clients which
support a compatible (EC)DHE group but do not predict it in the
"key_share" extension? As a client, do you correctly handle a
HelloRetryRequest from the server?
Cryptographic details: Cryptographic details:
- What countermeasures do you use to prevent timing attacks - What countermeasures do you use to prevent timing attacks
[TIMING]? [TIMING]?
- When verifying RSA signatures, do you accept both NULL and missing
parameters? Do you verify that the RSA padding doesn't have
additional data after the hash value? [FI06]
- When using Diffie-Hellman key exchange, do you correctly 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 7.4.1)?
- 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 4.2.5.1)? 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 C.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 4.2.5.1)? (see Section 4.2.5.1)?
- Do you verify signatures after making them to protect against RSA- - Do you verify signatures after making them to protect against RSA-
CRT key leaks? [FW15] CRT key leaks? [FW15]
B.5. Client Tracking Prevention C.5. Client Tracking Prevention
Clients SHOULD NOT reuse a session ticket for multiple connections.
Reuse of a session ticket allows passive observers to correlate
different connections. Servers that issue session tickets SHOULD
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
[RFC7230] might open six connections to a server. Servers SHOULD Clients SHOULD NOT reuse a ticket for multiple connections. Reuse of
issue new session tickets with every connection. This ensures that a ticket allows passive observers to correlate different connections.
clients are always able to use a new session ticket when creating a Servers that issue tickets SHOULD offer at least as many tickets as
new connection. the number of connections that a client might use; for example, a web
browser using HTTP/1.1 [RFC7230] might open six connections to a
server. Servers SHOULD issue new tickets with every connection.
This ensures that clients are always able to use a new ticket when
creating a new connection.
B.6. Unauthenticated Operation C.6. Unauthenticated Operation
Previous versions of TLS offered explicitly unauthenticated cipher Previous versions of TLS offered explicitly unauthenticated cipher
suites based on anonymous Diffie-Hellman. These modes have been suites based on anonymous Diffie-Hellman. These modes have been
deprecated in TLS 1.3. However, it is still possible to negotiate deprecated in TLS 1.3. However, it is still possible to negotiate
parameters that do not provide verifiable server authentication by parameters that do not provide verifiable server authentication by
several methods, including: several methods, including:
- Raw public keys [RFC7250]. - Raw public keys [RFC7250].
- Using a public key contained in a certificate but without - Using a public key contained in a certificate but without
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attacks and therefore unsafe for general use. However, it is also attacks and therefore unsafe for general use. However, it is also
possible to bind such connections to an external authentication possible to bind such connections to an external authentication
mechanism via out-of-band validation of the server's public key, mechanism via out-of-band validation of the server's public key,
trust on first use, or channel bindings [RFC5929]. [[NOTE: TLS 1.3 trust on first use, or channel bindings [RFC5929]. [[NOTE: TLS 1.3
needs a new channel binding definition that has not yet been needs a new channel binding definition that has not yet been
defined.]] If no such mechanism is used, then the connection has no defined.]] If no such mechanism is used, then the connection has no
protection against active man-in-the-middle attack; applications MUST protection against active man-in-the-middle attack; applications MUST
NOT use TLS in such a way absent explicit configuration or a specific NOT use TLS in such a way absent explicit configuration or a specific
application profile. application profile.
Appendix C. Backward Compatibility Appendix D. 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 and
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. depreca