Applying GREASE to TLS Extensibility
draft-ietf-tls-grease-01

Document Type Active Internet-Draft (tls WG)
Last updated 2018-06-06
Replaces draft-davidben-tls-grease
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Network Working Group                                        D. Benjamin
Internet-Draft                                                    Google
Intended status: Informational                              June 6, 2018
Expires: December 8, 2018

                  Applying GREASE to TLS Extensibility
                        draft-ietf-tls-grease-01

Abstract

   This document describes GREASE (Generate Random Extensions And
   Sustain Extensibility), a mechanism to prevent extensibility failures
   in the TLS ecosystem.  It reserves a set of TLS protocol values that
   may be advertised to ensure peers correctly handle unknown values.

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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   This Internet-Draft will expire on December 8, 2018.

Copyright Notice

   Copyright (c) 2018 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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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  GREASE Values . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Client-Initiated Extension Points . . . . . . . . . . . . . .   4
     3.1.  Client Behavior . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Server Behavior . . . . . . . . . . . . . . . . . . . . .   5
   4.  Server-Initiated Extension Points . . . . . . . . . . . . . .   6
     4.1.  Server Behavior . . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Client Behavior . . . . . . . . . . . . . . . . . . . . .   6
   5.  Sending GREASE Values . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The TLS protocol [I-D.ietf-tls-tls13] includes several points of
   extensibility, including the list of cipher suites and the list of
   extensions.  The values in these lists identify implementation
   capabilities.  TLS follows a model where one side, usually the
   client, advertises capabilities and the peer, usually the server,
   selects them.  The responding side must ignore unknown values so that
   new capabilities may be introduced to the ecosystem while maintaining
   interoperability.

   However, bugs may cause an implementation to reject unknown values.
   It will interoperate with existing peers, so the mistake may spread
   through the ecosystem unnoticed.  Later, when new values are defined,
   updated peers will discover that the metaphorical joint in the
   protocol has rusted shut and that the new values cannot be deployed
   without interoperability failures.

   To avoid this problem, this document reserves some currently unused
   values for TLS implementations to advertise at random.  Correctly
   implemented peers will ignore these values and interoperate.  Peers
   that do not tolerate unknown values will fail to interoperate,
   revealing the mistake before it is widespread.

   In keeping with the rusted joint metaphor, this technique is named
   GREASE (Generate Random Extensions And Sustain Extensibility).

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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