Every message sent through Synapse is individually encrypted using the Signal Protocol, widely regarded as the most secure messaging protocol available. The protocol combines the Extended Triple Diffie-Hellman (X3DH) key agreement with the Double Ratchet algorithm.

Quantum computers may one day break the elliptic-curve cryptography that underpins most encrypted messaging today. Synapse is ready. We use the PQXDH (Post-Quantum Extended Diffie-Hellman) protocol with ML-KEM-768, a NIST-standardized lattice-based key encapsulation mechanism.

This means messages encrypted today remain safe even if quantum computers become powerful enough to break classical encryption in the future. This is not a theoretical concern — it is a known attack vector called "harvest now, decrypt later."

Synapse is built so that we structurally cannot access your communications. Private encryption keys are generated and stored exclusively on your devices — in the iOS Secure Enclave or Keychain. They never leave the device, and they are never transmitted to our servers.

Your local message database is encrypted with SQLCipher. Even if someone gained physical access to your device, they would need your authentication credentials to access any data.

Most encrypted messaging platforms protect message content but still expose metadata — who is talking to whom, when, and how often. Synapse uses Sealed Sender technology to encrypt the sender's identity, reducing the metadata footprint of your communications.

Voice calls use peer-to-peer WebRTC connections encrypted with DTLS-SRTP. Audio data travels directly between devices without passing through our servers. Call signaling is routed through our secure SignalR infrastructure with end-to-end encryption.