Applying GREASE to TLS Extensibility
draft-ietf-tls-grease-00

Document Type Active Internet-Draft (tls WG)
Last updated 2017-01-18
Replaces draft-davidben-tls-grease
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Network Working Group                                        D. Benjamin
Internet-Draft                                                    Google
Intended status: Informational                          January 18, 2017
Expires: July 22, 2017

                  Applying GREASE to TLS Extensibility
                        draft-ietf-tls-grease-00

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 by clients to ensure servers 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.

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   This Internet-Draft will expire on July 22, 2017.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Benjamin                  Expires July 22, 2017                 [Page 1]
Internet-Draft    Applying GREASE to TLS Extensibility      January 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  GREASE Values . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Client Behavior . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Server Behavior . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   The TLS protocol [RFC5246] 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 clients advertise capabilities and servers
   select them.  It is required that servers ignore unknown values so
   that new capabilities may be introduced to the ecosystem while
   maintaining interoperability.

   However, bugs may cause a server to reject unknown values.  These
   broken servers will interoperate with existing clients, so the
   mistake may spread through the ecosystem unnoticed.  Later, when new
   values are defined, updated clients 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 clients to advertise at random.  Correct server
   implementations will ignore these values and interoperate.  Servers
   that do not tolerate unknown values will fail to interoperate with
   existing clients, revealing the mistake before it is widespread.
   This document reserves such values in the TLS cipher suite,
   extension, named group [RFC4492], and ALPN [RFC7301] registries.

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

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].
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