The Messaging Layer Security (MLS) Protocol
draft-ietf-mls-protocol-07
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2019-07-08
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draft-barnes-mls-protocol
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benjamin.beurdouche@ens.fr, karthikeyan.bhargavan@inria.fr, cas.cremers@cs.ox.ac.uk, alan@wire.com, singuva@twitter.com, kwonal@mit.edu, ekr@rtfm.com, thyla.van.der@merwe.tech
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Network Working Group R. Barnes
Internet-Draft Cisco
Intended status: Informational B. Beurdouche
Expires: January 9, 2020 Inria
J. Millican
Facebook
E. Omara
Google
K. Cohn-Gordon
University of Oxford
R. Robert
Wire
July 08, 2019
The Messaging Layer Security (MLS) Protocol
draft-ietf-mls-protocol-07
Abstract
Messaging applications are increasingly making use of end-to-end
security mechanisms to ensure that messages are only accessible to
the communicating endpoints, and not to any servers involved in
delivering messages. Establishing keys to provide such protections
is challenging for group chat settings, in which more than two
clients need to agree on a key but may not be online at the same
time. In this document, we specify a key establishment protocol that
provides efficient asynchronous group key establishment with forward
secrecy and post-compromise security for groups in size ranging from
two to thousands.
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 January 9, 2020.
Barnes, et al. Expires January 9, 2020 [Page 1]
Internet-Draft MLS July 2019
Copyright Notice
Copyright (c) 2019 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 . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Change Log . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Basic Assumptions . . . . . . . . . . . . . . . . . . . . . . 7
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
5. Ratchet Trees . . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Tree Computation Terminology . . . . . . . . . . . . . . 10
5.2. Ratchet Tree Nodes . . . . . . . . . . . . . . . . . . . 13
5.3. Views of a Ratchet Tree . . . . . . . . . . . . . . . . . 14
5.4. Ratchet Tree Updates . . . . . . . . . . . . . . . . . . 15
5.5. Synchronizing Views of the Tree . . . . . . . . . . . . . 16
6. Cryptographic Objects . . . . . . . . . . . . . . . . . . . . 17
6.1. Curve25519, SHA-256, and AES-128-GCM . . . . . . . . . . 18
6.1.1. P-256, SHA-256, and AES-128-GCM . . . . . . . . . . . 19
6.2. Credentials . . . . . . . . . . . . . . . . . . . . . . . 20
6.3. Tree Hashes . . . . . . . . . . . . . . . . . . . . . . . 20
6.4. Group State . . . . . . . . . . . . . . . . . . . . . . . 21
6.5. Direct Paths . . . . . . . . . . . . . . . . . . . . . . 23
6.6. Key Schedule . . . . . . . . . . . . . . . . . . . . . . 24
6.7. Encryption Keys . . . . . . . . . . . . . . . . . . . . . 26
7. Initialization Keys . . . . . . . . . . . . . . . . . . . . . 27
8. Message Framing . . . . . . . . . . . . . . . . . . . . . . . 28
8.1. Metadata Encryption . . . . . . . . . . . . . . . . . . . 30
8.2. Content Signing and Encryption . . . . . . . . . . . . . 31
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