[MLS] Revised MLS charter

Sean Turner <sean@sn3rd.com> Fri, 13 April 2018 18:09 UTC

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From: Sean Turner <sean@sn3rd.com>
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Date: Fri, 13 Apr 2018 14:09:20 -0400
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Subject: [MLS] Revised MLS charter
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The charter tweaks made since the BOF include tweaking (and reordering) some of the “property” bullets:
- added message confidentiality
- message authentication changed to message integrity and authentication

I know that Ben Schwartz mentioned that we should look at our “full compromise” definition, but in reviewing it the way it’s used in FS and PCS property bullets it looks okay to me.  But, maybe Ben can elaborate a bit.

Anyway at this point, here’s what we’re working with:

Messaging Layer Security (MLS) Charter (DRAFT)

Several Internet applications have a need for group key establishment
and message protection protocols with the following properties:

o Message Confidentiality - Messages can only be read
   by members of the group
o Message Integrity and Authentication - Each message
   has been sent by an authenticated sender, and has
   not been tampered with
o Membership Authentication - Each participant can verify
   the set of members in the group
o Asynchronicity - Keys can be established without any
   two participants being online at the same time
o Forward secrecy - Full compromise of a node at a point
   in time does not reveal past messages sent within the group
o Post-compromise security - Full compromise of a node at a
   point in time does not reveal future messages sent within the group
o Scalability - Resource requirements that have good scaling in the
   size of the group (preferably sub-linear)

Several widely-deployed applications have developed their own
protocols to meet these needs. While these protocols are similar,
no two are close enough to interoperate. As a result, each application
vendor has had to maintain their own protocol stack and independently
build trust in the quality of the protocol. The primary goal of this
working group is to develop a standard messaging security protocol
so that applications can share code, and so that there can be shared
validation of the protocol (as there has been with TLS 1.3). 

It is not a goal of this group to enable interoperability / federation
between messaging applications beyond the key establishment,
authentication, and confidentiality services.  Full interoperability
would require alignment at many different layers beyond security,
e.g., standard message transport and application semantics.  The
focus of this work is to develop a messaging security layer that
different applications can adapt to their own needs.

While authentication is a key goal of this working group, it is not
the objective of this working group to develop new authentication
technologies.  Rather, the security protocol developed by this
group will provide a way to leverage existing authentication
technologies to associate identities with keys used in the protocol,
just as TLS does with X.509.

In developing this protocol, we will draw on lessons learned from
several prior message-oriented security protocols, in addition to
the proprietary messaging security protocols deployed within
existing applications:

o S/MIME - ​https://tools.ietf.org/html/rfc5751
o OpenPGP - ​https://tools.ietf.org/html/rfc4880
o Off the Record - ​https://otr.cypherpunks.ca/Protocol-v3-4.1.1.html
o Signal - ​https://signal.org/docs/

The intent of this working group is to follow the pattern of
TLS 1.3, with specification, implementation, and verification
proceeding in parallel.  By the time we arrive at RFC, we
hope to have several interoperable implementations as well
as a thorough security analysis.

The specifications developed by this working group will be
based on pre-standardization implementation and deployment
experience, and generalizing the design described in:

o draft-omara-mls-architecture
o draft-barnes-mls-protocol

Note that consensus is required both for changes to the current
protocol mechanisms and retention of current mechanisms. In
particular, because something is in the initial document set does
not imply that there is consensus around the feature or around
how it is specified.

May 2018 - Initial working group documents for architecture and key management
Sept 2018 - Initial working group document adopted for message protection
Jan 2019 - Submit architecture document to IESG as Informational
Jun 2019 - Submit key management protocol to IESG as Proposed Standard
Sept 2019 - Submit message protection protocol to IESG as Proposed Standard