Network Working Group L. Pardue Internet-Draft A. Ramine Intended status: Standards Track Cloudflare Expires: 17 September 2021 16 March 2021 Reserving the clear ALPN Protocol ID draft-pardue-httpbis-dont-be-clear-00 Abstract HTTP Alternative Services (Alt-Svc) are identified by a tuple of Application-Protocol Layer Negotiation (ALPN) protocol identifier, a host and a port. The wire format for Alt-Svc is defined in ABNF and encodes this tuple or the keyword "clear", which has a special meaning. This memo reserves the ALPN protocol identifier "clear" to reduce the chances of accidental aliasing with the "clear" keyword. Note to Readers _RFC EDITOR: please remove this section before publication_ Source code and issues list for this draft can be found at https://github.com/LPardue/draft-pardue-httpbis-dont-be-clear (https://github.com/LPardue/draft-pardue-httpbis-dont-be-clear). 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 17 September 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. Pardue & Ramine Expires 17 September 2021 [Page 1] Internet-Draft Reserving clear March 2021 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 1.1. Conventions and Definitions . . . . . . . . . . . . . . . 2 2. Aliasing and Avoidance . . . . . . . . . . . . . . . . . . . 2 3. Security Considerations . . . . . . . . . . . . . . . . . . . 3 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 4.1. Registration of "clear" Identification String . . . . . . 3 5. Normative References . . . . . . . . . . . . . . . . . . . . 3 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 4 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction HTTP Alternative Services (Alt-Svc) [ALTSVC] are identified by a tuple of Application-Protocol Layer Negotiation (ALPN) [ALPN] protocol identifier, a host and a port. The wire format for Alt-Svc is defined in ABNF and encodes this tuple or the keyword "clear", which has a special meaning. This memo reserves the ALPN protocol identifier "clear" to reduce the chances of accidental aliasing with the "clear" keyword. 1.1. Conventions and Definitions 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. Aliasing and Avoidance [ALTSVC] Section 3 defines the Alt-Svc header field using ABNF. It requires a custom parser, which introduces a possibility for custom implementation errors. The Alt-Svc header field value can either be the keyword "clear" - a special value that invalidates cached alternative services, or a list of "alt-value", that includes an encoded ALPN protocol identifier [ALPN]. There is a chance that someone unwittingly defines the ALPN protocol identifier "clear" for Pardue & Ramine Expires 17 September 2021 [Page 2] Internet-Draft Reserving clear March 2021 genuine purposes but is unaware of the use of protocol identifiers in Alternative Services. This could trigger Alt-Svc parser errors that might lead to confusion between the keyword with the protocol identifier use. Since the "clear" keyword has special meaning, confusion might lead to detrimental effects. To prevent unintended aliasing, this document registers the "clear" ALPN protocol identifier. It relates to no actual application-layer protocol, effectively reserving the code point and preventing any unintended aliasing. 3. Security Considerations Broken Alt-Svc header field parsers might confuse a "clear" keyword with a "clear" ALPN protocol identifier. This could invalidate Alternative Service cache state but a conformant client should fall back safely as described in Section 2.4 of [ALTSVC]. 4. IANA Considerations 4.1. Registration of "clear" Identification String This document creates a new registration, "clear", in the "Application-Layer Protocol Negotiation (ALPN) Protocol IDs" registry established in [ALPN]. The "clear" string is a reserved value that does not identify any protocol: Protocol: Reserved Identification Sequence: 0x63 0x6C 0x65 0x61 0x72 ("clear") Specification: This document 5. Normative References [ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, "Transport Layer Security (TLS) Application-Layer Protocol Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, July 2014, . [ALTSVC] Nottingham, M., McManus, P., and J. Reschke, "HTTP Alternative Services", RFC 7838, DOI 10.17487/RFC7838, April 2016, . Pardue & Ramine Expires 17 September 2021 [Page 3] Internet-Draft Reserving clear March 2021 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Acknowledgments Your name here. Authors' Addresses Lucas Pardue Cloudflare Email: lucaspardue.24.7@gmail.com Anthony Ramine Cloudflare Email: nox@nox.paris Pardue & Ramine Expires 17 September 2021 [Page 4]