Vitalik: Signal is exploring phone number-free registration, but true privacy still requires "no cross-message correlation"

Ethereum co-founder Vitalik Buterin published a post noting that Signal recently announced it is exploring enabling users to register accounts without a phone number. He welcomed the move, stating it helps reduce reliance on the highly oligopolistic phone number system, lowers identity security risks stemming from SIM swap attacks, and makes it harder for governments to pressure Signal to ban local users on nationality grounds. Vitalik also pointed out that while this measure is superior to the status quo in privacy protection, it only delivers "confidentiality" rather than true anonymity, as metadata such as message send time, frequency, and recipient could still be used to piece together identity links. He argued that with the advancement of AI technology, long-term persistent anonymous accounts have become outdated, and the only defensible form of privacy is "unlinkability per message"—meaning no one except the communicating parties knows their identities. This direction is currently being explored and advanced by emerging communication tools like Session and SimpleX, as well as mixnet projects. Additionally, protection against spam and denial-of-service attacks will also be a key priority to address moving forward.