Re: [Mimi] Confirming adoption calls for draft-barnes-mimi-arch and draft-ralston-mimi-protocol

[Rohan Mahy <[e-mail]>]

Hi Brendan,

You characterized the state of the current draft as "freely" sharing a lot
of metadata with all the providers. I'd like to examine that a bit more.

Assuming each client follows the recommendation in the draft to use a
unique pseudonym per group (this implies only joining via join/invitation
links or knocks), the non-local providers know the following:
- the authorization policy of the group (broadly),
- how many MLS clients from each provider are in each group,
- how often each client sends messages,
- the authorization role(s) assigned to their anonymized users, and
- (if they reveal it) if there are multiple devices under the same
pseudonym.

While a user's local provider (which the user has chosen) is sort of
outside of the scope of MIMI, when it is a hub provider it will at least
need to disclose machine-readable privacy information for each of its
rooms. Each client gets to examine the room policy before they join and
before they accept any change to that policy. This is already way better
than the status quo. The metadata privacy extensions that Konrad and
Raphael are working on further improve the privacy situation.

If you think this is setting the privacy bar too low, I think it would be
reasonable to provide an outline of how you think MIMI could provide
similar functionality with even less metadata. IMO this doesn't need to be
an I-D, but at least a page-long email with bullet points.

Thanks,
-rohan

On Sat, Mar 23, 2024 at 3:45 PM Brendan McMillion <
[e-mail]> wrote:

> Providing the same privacy properties as Signal is incredibly difficult.
> Nobody is asking mimi to do that. However, the mimi protocol could be a
> neutral way for service providers to synchronize messages related to a
> given group. Whether a service provider chooses to receive messages in some
> exceptionally private way or not, would be the service provider's choice.
> But instead the drafts require duplicating state between the encryption
> layer and mimi layer, and this presupposes a certain inescapable amount of
> metadata leakage.
>
> On Sun, Mar 24, 2024 at 1:49 AM Rohan Mahy <[e-mail]> wrote:
>
>>
>>
>> On Sat, Mar 23, 2024, 02:38 Stephen Farrell <[e-mail]>
>> wrote:
>>
>>> Sounds like a classic loss for privacy.
>>>
>>
>> I argue it is the opposite. Today if you want to join a group chat on any
>> system other than Signal, the participants surrender much more metadata
>> than would be revealed to other providers under the proposed MIMI approach
>> with pseudonyms. In addition, the low metadata approaches (using techniques
>> such as privacy pass) that Konrad and Raphael are nurturing offer
>> substantial improvements to privacy.
>> If we publish a specification that requires all providers to provide at
>> least Signal-level metadata privacy, it is likely that we will end up with
>> neither interoperability nor privacy for the vast majority of users.
>> Thanks,
>> -rohan
>>
>>