Comment by xorcist

Signal absolutely knows who you correspond with. How could they otherwise route your chat messages?

They promise to throw this information away, which is nice but not possible to verify.

They also employ a roundabout way of encrypting this data, but as they rightly point out in their article that describes the scheme, encrypting or hashing phone numbers is not safe from a malicious attacker. The space of all possible phone numbers is so small that it could be brute forced in the blink of an eye.

You place all your trust in Signal (and Google/Apple) when you use them. That may be better than the alternatives, but it's still something we should be honest about.

That said, keep in mind that Signal and Google/Apple can also trivially backdoor your software, so unless you take specific precautions against that, the details of their middleman protection isn't terribly important.