MLS R. Mahy Internet-Draft Wire Intended status: Informational 22 October 2023 Expires: 24 April 2024 KeyPackage Context Extension for Message Layer Security (MLS) draft-mahy-mls-kp-context-00 Abstract This document describes a Message Layer Security (MLS) KeyPackage extension to convey a specific context or anticipated use for the KeyPackage. It is useful when a client provides the KeyPackage out- of-band to another client, and wants the specific KeyPackage used only in the anticipated context, for example a specific MLS group. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-mahy-mls-kp-context/. Discussion of this document takes place on the MLS Working Group mailing list (mailto:mls@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/mls/. Subscribe at https://www.ietf.org/mailman/listinfo/mls/. Source for this draft and an issue tracker can be found at https://github.com/rohan-wire/mls-kp-context/. 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 24 April 2024. Mahy Expires 24 April 2024 [Page 1] Internet-Draft MLS KeyPackage Context October 2023 Copyright Notice Copyright (c) 2023 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Extension Description . . . . . . . . . . . . . . . . . . . . 3 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 4.1. kp_context MLS Extension Type . . . . . . . . . . . . . . 3 4.2. urn:ietf:mls:kp_context:group_id URN registration . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. Normative References . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Terminology 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. The terms MLS client, MLS group, LeafNode, GroupContext, KeyPackage, GroupContextExtensions Proposal, Credential, CredentialType, and RequiredCapabilities have the same meanings as in the MLS protocol [I-D.ietf-mls-protocol]. 2. Introduction In some use cases of MLS, a client might wish to provide a KeyPackage to another client, but communicate that the specific KeyPackage is only to be used in a specific context, for example to join a specific MLS group. This document describes a KeyPackage extension that can convey that context. Mahy Expires 24 April 2024 [Page 2] Internet-Draft MLS KeyPackage Context October 2023 3. Extension Description This document specifies a KeyPackage MLS extension kp_context of type ContextPair. The syntax is described using the TLS Presentation Language [RFC8446] Each PerDomainTrustAnchor represents a specific identity domain which is expected and authorized to participate in the MLS group. It contains the domain name and the specific trust anchor used to validate identities for members in that domain. enum { reserved(0), groupid(1), uri(2), domain(3), jwk_thumbprint(4) (255) } ContextType; struct { ContextType context_type; opaque context_value; } ContextPair; ContextPair kp_context; 4. IANA Considerations This document proposes registration of a new MLS Extension Type. RFC EDITOR: Please replace XXXX throughout with the RFC number assigned to this document 4.1. kp_context MLS Extension Type The kp_context MLS Extension Type is used inside KeyPackage objects. It contains a URN Anchors object representing the trust anchors which are expected for identity validation inside the MLS group. Template: Value: 0x000B Name: kp_context Message(s): This extension may appear in KeyPackage objects Recommended: Y Reference: RFC XXXX Mahy Expires 24 April 2024 [Page 3] Internet-Draft MLS KeyPackage Context October 2023 4.2. urn:ietf:mls:kp_context:group_id URN registration Namespace Identifier: Requested of IANA (formal) or assigned by IANA (informal). Version: 1 Date: 2023-08-01 Registrant: Rohan Mahy rohan.ietf@gmail.com Purpose: Described in Section 3 of RFCXXXX. Syntax: Described in Section 3 of RFCXXXX. Assignment: Described in Section 4.1 of RFCXXXX. Security and Privacy: Described in Section 5 of RFCXXXX. Interoperability: Described in Section 3 of this document. Resolution: Described in Section 3 of this document. Documentation: RFCXXXX Additional Information: none Revision Information: n/a 5. Security Considerations The Security Considerations of MLS apply. The use of this extension may reveal the client's intentions or wishes in an out-of-band protocol, which may have weaker privacy protections than MLS handshake messages. 6. Normative References [I-D.ietf-mls-protocol] Barnes, R., Beurdouche, B., Robert, R., Millican, J., Omara, E., and K. Cohn-Gordon, "The Messaging Layer Security (MLS) Protocol", Work in Progress, Internet- Draft, draft-ietf-mls-protocol-20, 27 March 2023, . Mahy Expires 24 April 2024 [Page 4] Internet-Draft MLS KeyPackage Context October 2023 [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, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . Author's Address Rohan Mahy Wire Email: rohan.mahy@wire.com Mahy Expires 24 April 2024 [Page 5]