Re:Large-Scale Abuse of Contact Discovery in Mobile Messenge...
by AlexCoventry on Monday April 19, 2021 @06:41PM
(#26868690)
> SGX. This in itself is its own can of worms, but assuming it's secure
It likely doesn't really add much security. Anyone capable of running processes on the chip hosting the SGX enclave can probably run a side-channel attack to recover the necessary keys. I was very disappointed that Signal took that approach.
With Matrix you still end up trusting the server sysadmin (both in terms of ethics and technical abilities), it's not like it solves the problem for mass communication where at least one user has to agree on a 3rd-party instance.
> those contacts connect to Signal with an IP address and are doing other things like updating their profile or registering their delivery keys for their account from that same IP address.
Correct me if I'm wrong, but I think that happens within SGX. This in itself is its own can of worms, but assuming it's secure, I don't think you can do this association IP / account that easily. At least it seems so easy to work around that I would expect it to be like this (given that they already use SGX for other things). Now of course SGX is not secure, but it still makes the attacks more expensive and complex than they would be otherwise. If you have access to a Wire server, it would take you minutes to get all the group memberships of one user. If you have access to a Signal server, you'd need to log connections over some time, and do some statistical analysis to extract useful information. Not impossible, but far more costly and less reliable.
In terms of privacy Wire might be better with respect to the phone number requirement, but otherwise Signal has an edge.
The IP address is also something you can solve independently (VPN / Tor), so it makes sense not to solve it within Signal. But it would be nice to have some integration with Tor eventually.