Internet Engineering Task Force (IETF) D. Benjamin
Request for Comments: 8740 Google LLC
Updates: 7540 February 2020
Category: Standards Track
ISSN: 2070-1721
Using TLS 1.3 with HTTP/2
Abstract
This document updates RFC 7540 by forbidding TLS 1.3 post-handshake
authentication, as an analog to the existing TLS 1.2 renegotiation
restriction.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8740.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction
2. Requirements Language
3. Post-Handshake Authentication in HTTP/2
4. Other Post-Handshake TLS Messages in HTTP/2
5. Security Considerations
6. IANA Considerations
7. References
7.1. Normative References
7.2. Informative References
Author's Address
1. Introduction
TLS 1.2 [RFC5246] and earlier versions of TLS support renegotiation,
a mechanism for changing parameters and keys partway through a
connection. This was sometimes used to implement reactive client
authentication in HTTP/1.1 [RFC7230], where the server decides
whether or not to request a client certificate based on the HTTP
request.
HTTP/2 [RFC7540] multiplexes multiple HTTP requests over a single
connection, which is incompatible with the mechanism above. Clients
cannot correlate the certificate request with the HTTP request that
triggered it. Thus, Section 9.2.1 of [RFC7540] forbids
renegotiation.
TLS 1.3 [RFC8446] removes renegotiation and replaces it with separate
post-handshake authentication and key update mechanisms. Post-
handshake authentication has the same problems with multiplexed
protocols as TLS 1.2 renegotiation, but the prohibition in [RFC7540]
only applies to renegotiation.
This document updates HTTP/2 [RFC7540] to similarly forbid TLS 1.3
post-handshake authentication.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Post-Handshake Authentication in HTTP/2
HTTP/2 servers MUST NOT send post-handshake TLS 1.3
CertificateRequest messages. HTTP/2 clients MUST treat such messages
as connection errors (see Section 5.4.1 of [RFC7540]) of type
PROTOCOL_ERROR.
[RFC7540] permitted renegotiation before the HTTP/2 connection
preface to provide confidentiality of the client certificate. TLS
1.3 encrypts the client certificate in the initial handshake, so this
is no longer necessary. HTTP/2 servers MUST NOT send post-handshake
TLS 1.3 CertificateRequest messages before the connection preface.
The above applies even if the client offered the
"post_handshake_auth" TLS extension. This extension is advertised
independently of the selected Application-Layer Protocol Negotiation
(ALPN) protocol [RFC7301], so it is not sufficient to resolve the
conflict with HTTP/2. HTTP/2 clients that also offer other ALPN
protocols, notably HTTP/1.1, in a TLS ClientHello MAY include the
"post_handshake_auth" extension to support those other protocols.
This does not indicate support in HTTP/2.
4. Other Post-Handshake TLS Messages in HTTP/2
[RFC8446] defines two other messages that are exchanged after the
handshake is complete: KeyUpdate and NewSessionTicket.
KeyUpdate messages only affect TLS itself and do not require any
interaction with the application protocol. HTTP/2 implementations
MUST support key updates when TLS 1.3 is negotiated.
NewSessionTicket messages are also permitted. Though these interact
with HTTP when early data is enabled, these interactions are defined
in [RFC8470] and are allowed for in the design of HTTP/2.
Unless the use of a new type of TLS message depends on an interaction
with the application-layer protocol, that TLS message can be sent
after the handshake completes.
5. Security Considerations
This document resolves a compatibility concern between HTTP/2 and TLS
1.3 when supporting post-handshake authentication with HTTP/1.1.
This lowers the barrier for deploying TLS 1.3, a major security
improvement over TLS 1.2.
6. IANA Considerations
This document has no IANA actions.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
7.2. Informative References
[RFC8470] Thomson, M., Nottingham, M., and W. Tarreau, "Using Early
Data in HTTP", RFC 8470, DOI 10.17487/RFC8470, September
2018, <https://www.rfc-editor.org/info/rfc8470>.
Author's Address
David Benjamin
Google LLC
Email: davidben@google.com
