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title: KeyPackage Context Extension for Message Layer Security (MLS) abbrev: MLS KeyPackage Context docname: draft-mahy-mls-kp-context-latest ipr: trust200902 submissiontype: IETF # also: "independent", "IAB", or "IRTF" area: art workgroup: MLS area: sec category: info keyword:

  • mls extension
  • keypackage context
  • keypackage extension

stand_alone: yes pi: [toc, sortrefs, symrefs]

venue: group: MLS type: Working Group mail: [email protected] arch: https://mailarchive.ietf.org/arch/browse/mls/ github: rohan-wire/mls-kp-context/

latest: https://github.com/rohan-wire/mls-kp-context/latest

author:

normative:

informative:

--- 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.

--- middle

Terminology

{::boilerplate bcp14-tagged}

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}}.

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.

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<V>;
} ContextPair;

ContextPair kp_context;

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

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

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
     [email protected]

   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

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.

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