Applying Generate Random Extensions And Sustain Extensibility (GREASE) to TLS Extensibility
RFC 8701
Document | Type |
RFC - Informational
(January 2020; No errata)
Was draft-ietf-tls-grease (tls WG)
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Author | David Benjamin | |||||
Last updated | 2020-03-09 | |||||
Replaces | draft-davidben-tls-grease | |||||
Stream | Internent Engineering Task Force (IETF) | |||||
Formats | plain text html xml pdf htmlized (tools) htmlized bibtex | |||||
Reviews | ||||||
Additional Resources |
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Stream | WG state | Submitted to IESG for Publication | ||||
Document shepherd | Sean Turner | |||||
Shepherd write-up | Show (last changed 2019-08-15) | |||||
IESG | IESG state | RFC 8701 (Informational) | ||||
Action Holders |
(None)
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Consensus Boilerplate | Yes | |||||
Telechat date | ||||||
Responsible AD | Benjamin Kaduk | |||||
Send notices to | Sean Turner <sean@sn3rd.com> | |||||
IANA | IANA review state | IANA OK - Actions Needed | ||||
IANA action state | RFC-Ed-Ack |
Internet Engineering Task Force (IETF) D. Benjamin Request for Comments: 8701 Google LLC Category: Informational January 2020 ISSN: 2070-1721 Applying Generate Random Extensions And Sustain Extensibility (GREASE) to TLS Extensibility 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 document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8701. 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 1.1. Requirements Language 2. GREASE Values 3. Client-Initiated Extension Points 3.1. Client Behavior 3.2. Server Behavior 4. Server-Initiated Extension Points 4.1. Server Behavior 4.2. Client Behavior 5. Sending GREASE Values 6. IANA Considerations 7. Security Considerations 8. Normative References Acknowledgments Author's Address 1. Introduction The TLS protocol [RFC8446] includes several points of extensibility, including the list of cipher suites and several lists of extensions. The values transmitted 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 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 called "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", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 2. GREASE Values This document reserves a number of TLS protocol values, referred to as GREASE values. These values were allocated sparsely to discourage server implementations from conditioning on them. For convenience, they were also chosen so all types share a number scheme with a consistent pattern while avoiding collisions with any existing applicable registries in TLS. The following values are reserved as GREASE values for cipher suites and Application-Layer Protocol Negotiation (ALPN) [RFC7301] identifiers: {0x0A,0x0A} {0x1A,0x1A} {0x2A,0x2A} {0x3A,0x3A} {0x4A,0x4A} {0x5A,0x5A} {0x6A,0x6A} {0x7A,0x7A} {0x8A,0x8A} {0x9A,0x9A} {0xAA,0xAA} {0xBA,0xBA} {0xCA,0xCA}Show full document text