Signal PQXDH

Signal's post-quantum extended Diffie-Hellman handshake, the first mass-market messenger deployment of a NIST-selected KEM.

Core Principles & Analysis

• Upgraded the X3DH initial handshake so newly captured sessions resist future quantum decryption.
• Chose the highest parameter set, Kyber-1024, prioritizing margin over bandwidth.
• Published with a formal security analysis developed alongside academic reviewers.

Specifications & Metrics

• PLATFORM: Signal
• MECHANISM: X25519 + Kyber-1024
• SINCE: 2023