Secure Negotiation of Incompatible Protocols in TLS
draft-thomson-tls-snip-00

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Author Martin Thomson 
Last updated 2020-07-13
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Network Working Group                                         M. Thomson
Internet-Draft                                                   Mozilla
Intended status: Informational                              13 July 2020
Expires: 14 January 2021

          Secure Negotiation of Incompatible Protocols in TLS
                       draft-thomson-tls-snip-00

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
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 14 January 2021.

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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
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Incompatible Protocols and SVCB . . . . . . . . . . . . . . .   4
   4.  Authenticating Incompatible Protocols . . . . . . . . . . . .   4
   5.  Protocol Authentication Scope . . . . . . . . . . . . . . . .   5
     5.1.  SVCB Discovery Scope  . . . . . . . . . . . . . . . . . .   6
     5.2.  QUIC Version Negotiation  . . . . . . . . . . . . . . . .   6
     5.3.  Alternative Services  . . . . . . . . . . . . . . . . . .   6
     5.4.  Scope for Other Discovery Methods . . . . . . . . . . . .   7
   6.  Incompatible Protocol Selection . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

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 for 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
   protects against this attack by ensuring that the server is aware of
   all options the client supports and including those options and the
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