Re: [briar-devel] Gnunet

[Michael R. <mi...@br...>]

On 13/09/17 17:04, Darien Alonso wrote:
> 2017-08-18 11:57 GMT-04:00, Greg Troxel <gd...@le...>:
>> Sort of getting off topic, but I wonder about a way to have briar nodes
>> convey private messages sometimes (in the e2e-encrypted form of course).
>> I realize you don't want to flood this to all nodes or untrusted nodes,
>> for scaling and to avoid enabling traffic analysis.  In a region without
>> Internet, it would be nice to have messages flow via opportunistic
>> couriers, so that if A has addressed a message to C, meets and syncs
>> with B, and later B syncs with C, C will get the message.
>>
> 
> I agree with Greg and from my point of view this is the main feature a
> project like Briar must provide to allow keeping the information
> flowing in places or situations where internet is sensored or
> imposible. AFAIK briar aims to provide this feature.

I agree this would be a great capability to have, but it's not easy to
implement without undermining some of the other properties we're trying
to provide, such as privacy of contact relationships, privacy of group
subscriptions, and reasonable bandwidth consumption.

The simplest way of implementing this capability - sync every message to
every device - has unacceptable bandwidth overhead and allows a single
malicious user to flood the network.

If we limit the range of each message via a hop counter, we reveal
information about contact relationships. For example, Alice can check
whether her contacts Bob and Carol are contacts of each other by syncing
a message to Bob and seeing whether Carol syncs the message back to her
with a hop count of 2.

A similar problem applies to group subscriptions if we use a rule such
as "sync the message to every device that subscribes to the group, and
every device within two hops of a subscriber".

Cheers,
Michael