TLS 1.3 Extended Key Schedule
draft-jhoyla-tls-extended-key-schedule-02

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jhoyla                                                        J. Hoyland
Internet-Draft                                           Cloudflare Ltd.
Intended status: Standards Track                               C.A. Wood
Expires: March 13, 2021                                       Cloudflare
                                                       September 9, 2020

                     TLS 1.3 Extended Key Schedule
               draft-jhoyla-tls-extended-key-schedule-02

Abstract

   TLS 1.3 is sometimes used in situations where it is necessary to
   inject extra key material into the handshake.  This draft aims to
   describe methods for doing so securely.  This key material must be
   injected in such a way that both parties agree on what is being
   injected and why, and further, in what order.

Note to Readers

   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/
   (https://mailarchive.ietf.org/arch/browse/tls/).

   Source for this draft and an issue tracker can be found at
   https://github.com/jhoyla/draft-jhoyla-tls-key-injection
   (https://github.com/jhoyla/draft-jhoyla-tls-key-injection).

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 13, 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
   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
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   3
   3.  Key Schedule Extension  . . . . . . . . . . . . . . . . . . .   3
     3.1.  Handshake Secret Injection  . . . . . . . . . . . . . . .   3
     3.2.  Main Secret Injection . . . . . . . . . . . . . . . . . .   3
   4.  Key Schedule Injection Negotiation  . . . . . . . . . . . . .   4
   5.  Key Schedule Extension Structure  . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Introducing additional key material into the TLS handshake is a non-
   trivial process because both parties need to agree on the injection
   content and context.  If the two parties do not agree then an
   attacker may exploit the mismatch in so-called channel
   synchronization attacks, such as those described by [SLOTH].

   Injecting key material into the TLS handshake allows other protocols
   to be bound to the handshake.  For example, it may provide additional
   protections to the ClientHello message, which in the standard TLS
   handshake only receives protections after the server's Finished
   message has been received.  It may also permit the use of combined
   shared secrets, possibly from multiple key exchange algorithms, to be
   included in the key schedule.  This pattern is common for Post
   Quantum key exchange algorithms, as discussed in
   [I-D.ietf-tls-hybrid-design].

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   The goal of this document is to provide a standardised way for
   binding extra context into TLS 1.3 handshakes in a way that is easy