Axolotl, an asynchronous cryptographic protocol with perfect forward secrecy for long-lived sessions

Transcript

1. @FredericJacobs
2. What? Security, simplified. TextSecure RedPhone
3. TextSecure
4. Protocols
5. We live asynchronously
6. Perfect Forward Secrecy
7. Perfect Future Secrecy
8. Deniability
9. General Approach Message Protocols Session protocols Examples : PGP, S/MIME ! Asynchronous ! Problems: Conversation Integrity, forward secrecy, deniability Examples: OTR, SSL, SSH ! Synchronous ! Short-lived session Axolotl Examples: TextSecure, Pond ! Asynchronous with all great features of short lived protocols ! Forward secrecy, deniability, conversation integrity …
10. Axolotl
11. Protocols WhatsApp iMessage Threema MTProto (Telegram) SCIMP (SilentText) Axolotl (TextSecure) OTR End-to-End Encryption No Yes (no control on key management) Yes Yes Yes Yes Yes PFS No No No No Yes Yes Yes Perfect Future Secrecy No No No No No Yes Yes Multi-Party Encrypted Chats No Yes Yes No Yes Yes No Multi-Device Encrypted Chats No Yes No No No Yes (not yet implemented ) No
12. Axolotl Outline • Basic features! • Authentication • Handshake •  Forward-secrecy ratcheting • Advanced (not covered in this talk) • Multi-party • Multi-device
13. Contact Discovery
14. Authentication
15. TextSecure Server Prekey for Moxie? Ephemeral Prekey + Identity Key for Moxie
16. Handshaking
17. Moxie’s Identity Key My Identity Key Moxie’s ephemeral prekey My ephemeral key Shared Secret = HKDF(3-Way DH)
18. Ratcheting
19. OTR-Ratchet (three step ratchet)
20. SCIMP-Ratchet (hash-based ratchet)
21. OTR Ratchet Silent Circle Ratchet Excellent Perfect Forward & Future Secrecy Excellent Perfect Forward Secrecy. But if message key gets compromised, all future conversations will be compromised.
22. Axolotl-Ratchet
23. A leap into the future
24. Thanks Questions? Such Crypto Very Datalove Wow