Signal Community Debates Using Zero-Knowledge Proofs to End Phone Number Requirements

Users on the Signal Community forum and Hacker News are discussing the potential for account registration without a phone number, specifically through the use of zero-knowledge proofs (ZKPs). While Signal currently mandates a phone number for initial account creation, the conversation centers on whether the app's existing ZKP infrastructure could eventually eliminate this requirement while preventing spam.

Signal has already integrated ZKPs into its ecosystem to protect usernames. According to technical discussions on Hacker News, the platform uses ZKPs and a custom Ristretto 25519 hashing algorithm to ensure usernames are not stored in plaintext. This architecture prevents the server from easily linking a specific phone number to a username, providing a layer of separation between a user's primary identifier and their public handle.

The Identity Struggle

Historically, Signal has relied on phone numbers as the primary identifier for accounts. This dependency has been a recurring point of criticism for privacy advocates, as SIM cards are typically registered to real-world identities through government-mandated KYC (Know Your Customer) laws in many jurisdictions. To mitigate this, Signal introduced usernames, which allow users to communicate with others without sharing their phone numbers. However, the initial registration process still requires a valid number to establish the account.

Implications for Anonymity

Removing the phone number requirement would eliminate one of the last remaining links between a user's real-world identity and their encrypted communications. For activists, whistleblowers, and journalists operating in hostile environments, this shift would significantly enhance anonymity by removing the need for a SIM card, which can be tracked or seized by state actors. By decoupling the account from a telephony provider, the platform could move toward a model where identity is self-sovereign rather than tied to a corporate or state-monitored utility.

The Path Forward

The current debate focuses on whether the same ZKP logic used for usernames can be scaled to the registration process to maintain security without a central phone-based authority. While the community is actively exploring these possibilities, Signal has not officially announced a timeline or a technical roadmap for removing phone numbers from the registration flow. Observers are watching to see if the platform will move toward a fully decoupled identity system or maintain the phone number as a necessary barrier against automated bot registration. The resolution of this debate will likely determine if Signal can truly offer a registration process that is invisible to state surveillance.