Signal adds new cryptographic defense against quantum attacks

Signal announced SPQR, a post-quantum cryptographic component that augments its Double Ratchet into a Triple Ratchet by mixing keys from both classical and post-quantum sources (ML-KEM/CRYSTALS‑Kyber) via a KDF to provide forward secrecy and post‑compromise security. Developed with PQShield, AIST, and NYU, the design was formally verified (ProVerif) and the Rust implementation tested with hax, with ongoing continuous verification. SPQR will roll out gradually, remain backward compatible until universally deployed, and requires only that users keep clients updated.