[lima]

Exactly. The most important reason to use Signal is the trustworthiness of the developers. Moxie is a highly esteemed security researcher / public figure. I trust him to (1) implement the protocol properly (which is really hard) and (2) respect my privacy and (3) not sell out like WhatsApp did.

The thing is, as long as we're using phone numbers as user handles, you have to trust the provider with your phone book. Signal tries as hard as possible to avoid it (all phone numbers are hashed), but if they wanted, they could simply brute force all the hashes since the search space is so small. There's no good solution to this.

[vocatus_gate]

Would salting the hashes be an improvement?

I ask knowing very little about their security model.

[lima]

No, they're doing that already. The issue is that phone numbers are so short that you can just calculate the salted hash for all of them. You don't need any rainbow tables for that.