X3DH — initial key agreement
Extended triple Diffie-Hellman. Uses long-term + one-time prekeys. Alice + Bob derive a shared secret asynchronously (Bob doesn't need to be online).
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X3DH — initial key agreement
Extended triple Diffie-Hellman. Uses long-term + one-time prekeys. Alice + Bob derive a shared secret asynchronously (Bob doesn't need to be online).
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Ratchet 1: Diffie-Hellman
Each new message exchange advances the DH ratchet. New shared secret. Even if one key leaks, future keys are safe (post-compromise security).