Key setup for secure channel

• exchange nonces
• Alices generates random key K for the secure channel
• Alice sends K encrypted by Bob’s public key
• Both Alice and Bob sign the transcript of the protocol.
  • binds instance of the protocol to the nonces
  • ensures that there is no man in the middle

Steps 2 and 3 are replaceable by Diffie-Hellman (it is recommended to hash the result of DH). This is also little bit better because it is forward secure.