Signal Protocol Specifications
The Signal Protocol Specifications define the core cryptographic protocols that underpin Signal's end-to-end encrypted messaging. These include the X3DH (Extended Triple Diffie-Hellman) key agreement protocol for establishing shared secrets between parties, the Double Ratchet Algorithm for deriving new encryption keys per message, the PQXDH (Post-Quantum Extended Diffie-Hellman) protocol for quantum-resistant key agreement, and XEdDSA for EdDSA-compatible signature schemes. These specifications are published independently so they can be adopted by other projects beyond Signal itself.