[Cryptography] Apple Group FaceTime and end-to-end and encryption

[Christian Huitema]

On 6/6/2018 3:51 AM, Jerry Leichter wrote:
> Now Apple has announced that the next release of iOS will support group connections with up to 32 members.  I'm wondering "how they plan to do that".
>
> There are two components to the problem:
>
> 1.  Doing the necessary computations.  Recent iPhones certainly have the necessary compute power to handle mixing of 32 audio streams.  They also have GPU's that should be able to handle the compositing and other video processing.
> 2.  But ... you can only do computation *on data you actually receive*.  Sending all 31 audio streams to all phones at all times seems plausible.  Thirty one full video streams seems unrealistic.

I had to solve a very similar engineering problem for a chat application
on the X-box, about 10 years ago. What we did was organize the
participants in a spanning tree, picking the devices with the network
connections as nodes and the devices with the worse connections as
leaves. We controlled the branching of the tree so as to not overwhelm
the nodes. You get a structure in which each node-to-node or
leaf-to-node transmission is encrypted, but of course each member sees
the whole context. The spanning tree worked fine in practice, although
of course latency becomes a function of the diameter of the graph. I
have no idea what the folks at Apple chose to do, but yes, there are
solutions.

-- Christian Huitema
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