Re: [MLS] Proposal: Proposals (was: Laziness)

Stephen Farrell <stephen.farrell@cs.tcd.ie> Fri, 23 August 2019 12:26 UTC

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To: Raphael Robert <raphael=40wire.com@dmarc.ietf.org>
Cc: Richard Barnes <rlb@ipv.sx>, Messaging Layer Security WG <mls@ietf.org>
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Fri, 23 Aug 2019 13:26:03 +0100
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Subject: Re: [MLS] Proposal: Proposals (was: Laziness)
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Hiya,

On 23/08/2019 13:17, Raphael Robert wrote:
> The ghost user scenario is precisely what we want to avoid. In
> Richard’s Proposals draft, every Proposal has to be validated by a
> Commit message, and the latter can only be issued by an existing
> member of the group. Therefore the server still cannot control the
> group membership, it can rather only make proposals on how the
> membership list should be modified. Naturally we need to make sure
> that everything works as intended.

Sure, I get that. My concern is that I'm not clear how
such proposals could meaningfully be handled by members
in general - it seems like it could be quite a footgun.

Cheers,
S.

> 
>> On 23 Aug 2019, at 13:26, Stephen Farrell
>> <stephen.farrell@cs.tcd.ie> wrote:
>> 
>> 
>> Hiya,
>> 
>> On 23/08/2019 11:24, Raphael Robert wrote:
>>> Right now, Add and Remove handshake messages have to be signed by
>>> an existing member of the group. There is no way for the server
>>> to make any changes to the group membership.
>> 
>> Thanks. As you note in your other mail, that seems a bit
>> concerning, from a potentially ghostly point of view. My initial
>> reaction (again with the "benefit" of not having kept up to date
>> with the drafts:-) is that a service using MLS could put itself in
>> a position to do the same thing within the application layer if 
>> necessary, so it'd seem better for it not to be a feature of the
>> MLS protocol.
>> 
>> I've no opinion on the general idea of proposals, my concern is
>> only really about a non-member of the group (the server or anyone
>> else) being able to control group membership like that, for what I
>> guess would effectively be all applications using MLS.
>> 
>> Cheers, S.
>> 
>>> 
>>>> On 23 Aug 2019, at 11:08, Stephen Farrell 
>>>> <stephen.farrell@cs.tcd.ie> wrote:
>>>> 
>>>> Signed PGP part
>>>> 
>>>> Sorry for not following mls in detail but can you explain how:
>>>> 
>>>> On 22/08/2019 23:16, Richard Barnes wrote:
>>>>> 2. Allow some flavor of server-initiated Add and Remove
>>>> 
>>>> ...compares to the status quo ante?
>>>> 
>>>> Thanks, S. <0x5AB2FAF17B172BEA.asc>
>>>> 
>>>> 
>>> 
>>> 
>> <0x5AB2FAF17B172BEA.asc>
> 
> 
> 
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