Signal is building phone-number-free registration on zero-knowledge proofs
Registration without a phone number on Signal will use zero-knowledge proofs
Signal's Android app is gaining the scaffolding for numberless accounts: new login screens, username setup during registration, and a fresh zkgroup credential. Community members note that zero-knowledge proofs already underpin donation badges, backup payments, and groups, letting the server verify a user without identifying them. Signal staff confirm ZKP also checks username length and character set without revealing the name itself.
the great thing about Signal is the client is designed to already not trust the server. in fact you can show that Signal is perfectly safe without even looking at server code.