Signal is considering a new registration feature that would allow users to sign up without providing a phone number. This approach relies on zero-knowledge proofs (ZKP), a cryptographic technique already used by Signal for donation badges, backup payments, and group management. ZKP enables verification of information without revealing the underlying data, enhancing privacy by preventing the server from linking users to specific donations or groups. The Signal client is designed to operate without trusting the server, which helps maintain security even without examining server code. In this context, ZKP could verify username properties like character set and length without exposing the actual username. However, questions remain about the extent to which phone numbers can be completely unlinked from usernames and what data might persist locally or on servers. There are concerns that unlinking phone numbers might not be absolute, and simply removing phone number requirements could invite abuse. For example, spammers might exploit the system by registering multiple accounts after unlinking phone numbers, potentially creating unlimited free accounts. To mitigate this, Signal might implement cooldown periods between registrations, though the optimal duration is uncertain, as it must balance usability and spam prevention. Signal has yet to clarify the technical details and privacy implications of this potential feature, but it represents a significant step toward enhancing user privacy in messaging platforms.