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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.

 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (https://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

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