Asynchronous Bidirectional Secure Channels¶
links: AC2 TOC - Secure messaging and channels - Index
Forward secrecy¶
If the long-term secret key is compromised, decryption is only possible for future sessions, not for past sessions.
Future secrecy¶
If a session key is compromised, it doesn't affect the security of future session keys.
Silent Circle Instant Message Protocol (SCIMP)¶
Forward Secrecy
Protocol which uses hashes of the private key to encrypt data instead of using the actual key. This leads to forward secrecy because if the current key (\(h_3(h_2(h_1(k)))\)) gets leaked the attacker can't go back to previous hashes of the key. Past encryptions stay secure.
Axolotl / Signal Protocol¶
Forward & Future Secrecy
The protocol combines the Double Ratchet algorithm, prekeys, and a triple Elliptic-curve Diffie–Hellman (Secure Channels#Triple Diffie-Hellman (3DH)|3DH) handshake, and uses Curve25519, AES-256, and HMAC-SHA256 as primitives.
