Draft: draft-ietf-mls-architecture

Commentary: This PR addresses 
 Thanks ! 
 In the context of this document , the meaning of the term Messaging Service ( MS ) seems a little unclear to me . The document states that the protocol is intended to be embedded in a concrete protocol such as XMPP . However , is a MS meant to be a messaging service such as SMS or MMS ? Or a service on the application layer , such as FB or  ? Essentially who provides / controls the AS and DS ? I would be grateful for some clarification on this . Thanks . 
 It is meant to mean application layer , would changing that to " service provider " work better for you ? 
 Thank you . I do think that the term service provider is less ambiguous . 
  , will fix soon . 
 I can make a PR , if you want ? 
 Sure , please go for it . 
 Fixed by
End-to-end security is a requirement for instant messaging systems
and is commonly deployed in many such systems.  In this context,
"end-to-end" captures the notion that users of the system enjoy some
level of security - with the precise level depending on the system
design - even when the messaging service they are using performs
unsatisfactorily.
End-to-end security is a requirement for instant messaging systems
and is commonly deployed in many such systems.  In this context,
"end-to-end" captures the notion that users of the system enjoy some
level of security - with the precise level depending on the system
design - even when the service provider they are using performs
unsatisfactorily.
Informally, a group is a set of users who possibly use multiple
endpoint devices to interact with the Messaging Service (MS).  A
group may be as small as two members (the simple case of person to
person messaging) or as large as thousands.
Informally, a group is a set of users who possibly use multiple
endpoint devices to interact with the Service Provider (SP).  A group
may be as small as two members (the simple case of person to person
messaging) or as large as thousands.
Alice, Bob and Charlie create accounts with a messaging service
and obtain credentials from the AS.
Alice, Bob and Charlie create accounts with a service provider and
obtain credentials from the AS.
While informally, a group can be considered to be a set of users
possibly using multiple endpoint devices to interact with the
Messaging Service, this definition is too simplistic.
While informally, a group can be considered to be a set of users
possibly using multiple endpoint devices to interact with the Service
Provider, this definition is too simplistic.
The protocol is designed in a way that limits the server-side (AS and
DS) metadata footprint.  The DS only persists data required for the
delivery of messages and avoids Personally Identifiable Information
(PII) or other sensitive metadata wherever possible.  A Messaging
Service provider that has control over both the AS and the DS, will
not be able to correlate encrypted messages forwarded by the DS, with
the initial public keys signed by the AS.
The protocol is designed in a way that limits the server-side (AS and
DS) metadata footprint.  The DS only persists data required for the
delivery of messages and avoids Personally Identifiable Information
(PII) or other sensitive metadata wherever possible.  A Service
Provider that has control over both the AS and the DS, will not be
able to correlate encrypted messages forwarded by the DS, with the
initial public keys signed by the AS.
A corollary to this statement is that the AS and the DS cannot read
the content of messages sent between Members as they are not Members
of the Group.  MLS optionally provides additional protections
regarding traffic analysis so as to reduce the ability of attackers,
or a compromised member of the messaging system, to deduce the
content of the messages depending on (for example) their size.  One
of these protections includes padding messages in order to produce
ciphertexts of standard length.  While this protection is highly
recommended it is not mandatory as it can be costly in terms of
performance for clients and the MS.
A corollary to this statement is that the AS and the DS cannot read
the content of messages sent between Members as they are not Members
of the Group.  MLS optionally provides additional protections
regarding traffic analysis so as to reduce the ability of attackers,
or a compromised member of the messaging system, to deduce the
content of the messages depending on (for example) their size.  One
of these protections includes padding messages in order to produce
ciphertexts of standard length.  While this protection is highly
recommended it is not mandatory as it can be costly in terms of
performance for clients and the SP.