Re:Reviewing the Cryptography Used by Signal
by grayhatter on Tuesday February 18, 2025 @03:28PM
(#43094644)
Is signal not able to tag and reduce the sealed envelope to a "final" destination network address?
I.e. is a sender able to prove that it's impossible for signal servers to do this?
Re:Reviewing the Cryptography Used by Signal
by some_furry on Tuesday February 18, 2025 @03:30PM
(#43094658)
I don't understand your question.
See https://signal.org/blog/sealed-sender/ and https://eprint.iacr.org/2019/1416 if you'd like descriptions for the protocols I'm trying to describe in HN comments.
Signal's server doesn't know who sent the message, since that information was Sealed.
Signal's server does know where to deliver the message to, based on a 96-bit random value generated client-side by the recipient (the delivery token). But it cannot know which user has which delivery token. To understand that, you need to look at the zero-knowledge credentials section of the code.
They could randomly drop messages sent to a specific targeted user's delivery token and block messages sent to that targeted user, but they have no way of knowing which user they're targeting. (Also, the client could just enroll a new one if this ever happened and Signal was somehow court-ordered to block delivery to a specific delivery token.)