Hi, I've been looking at the Axolotl Ratchet protocol and have a few questions:
- If a message is lost, it seems one must try to decrypt an incoming message with different keys, one after the other. This seems wasteful - why not maintain a "ratchet count" that can map directly to the right root key to use? - Key chaining means all previous keys in the chain are required. Why not instead "reuse" the original handshake? That is, initially Alice and Bob send their identity keys (IDa, IDb) and ephemeral keys (A0, B0). Now, if Alice wants to perform a ratchet, she will generate a new key pair (A1) and then perform the handshake again with IDa, IDb, A1, B0 (it will indicate it is using the B0 for the handshake). Bob will then create B1 and will perform 3DHE with IDa, IDb, A1, B1, ... This seems somewhat simpler than Axolotl, but allows a simpler handling of missing messages. What am I missing? Thanks, Sunny
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