Signal Community Debates Phone-Number-Free Signup Built on Zero-Knowledge Proofs

A Signal community thread digs into how the app might let people register without exposing a phone number, using the same zero-knowledge proof techniques Signal already relies on for donation badges, private group membership, and username validation. The core appeal is that ZKPs let the server verify a fact — that a username fits allowed length and character rules, for example — without learning the underlying data, and Signal’s client is deliberately built to distrust the server regardless.

Participants raise practical privacy questions the organization would need to answer before shipping such a feature: whether a phone number would be truly severed from a username, and what identifying remnants might linger on the device or server after ‘unlinking.’ Several posters are skeptical that decoupling is ever fully complete, and suggest that creating a fresh account without a number may be cleaner than retroactively unlinking one.

The discussion also surfaces the perennial tension between anonymity and abuse. If unlinking a number were free and repeatable, spammers could recycle a single number to spin up unlimited accounts, so commenters float rate-limiting via a registration cooldown — while acknowledging the window can’t be long enough to deter scammers without also frustrating legitimate users.