Secure Negotiation of Incompatible Protocols in TLS
draft-thomson-tls-snip-01

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Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Informational                            4 January 2021
Expires: 8 July 2021

          Secure Negotiation of Incompatible Protocols in TLS
                       draft-thomson-tls-snip-01

Abstract

   An extension is defined for TLS that allows a client and server to
   detect an attempt to force the use of less-preferred application
   protocol even where protocol options are incompatible.  This
   supplements application-layer protocol negotiation, which allows
   choices between compatible protocols to be authenticated.

Discussion Venues

   This note is to be removed before publishing as an RFC.

   Discussion of this document takes place on the TLS Working Group
   mailing list (tls@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/tls/.

   Source for this draft and an issue tracker can be found at
   https://github.com/martinthomson/snip.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 July 2021.

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Copyright Notice

   Copyright (c) 2021 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
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Incompatible Protocols and SVCB . . . . . . . . . . . . . . .   4
   4.  Authenticating Incompatible Protocols . . . . . . . . . . . .   4
   5.  Incompatible Protocol Selection . . . . . . . . . . . . . . .   6
   6.  Protocol Authentication Scope . . . . . . . . . . . . . . . .   7
     6.1.  The Default Scope . . . . . . . . . . . . . . . . . . . .   8
     6.2.  SVCB Scope  . . . . . . . . . . . . . . . . . . . . . . .   8
     6.3.  QUIC Version Negotiation Scope  . . . . . . . . . . . . .   8
   7.  Other Discovery Methods . . . . . . . . . . . . . . . . . . .   9
     7.1.  Alternative Services  . . . . . . . . . . . . . . . . . .   9
   8.  Operational Considerations  . . . . . . . . . . . . . . . . .  10
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   With increased diversity in protocol choice, some applications are
   able to use one of several semantically-equivalent protocols to
   achieve their goals.  This is particularly notable in HTTP where
   there are currently three distinct protocols: HTTP/1.1 [HTTP11],
   HTTP/2 [HTTP2], and HTTP/3 [HTTP3].  This is also true of protocols
   that support variants based on both TLS [TLS] and DTLS [DTLS].

   For protocols that are mutually compatible, Application-Layer
   Protocol Negotiation (ALPN; [ALPN]) provides a secure way to
   negotiate protocol selection.

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   In ALPN, the client offers a list of options in a TLS ClientHello and
   the server chooses the option that it most prefers.  A downgrade
   attack occurs where both client and server support a protocol that
   the server prefers more than than the selected protocol.  ALPN