Suppose there are three entities A, B, and C, where B and C are fully trusted, and the communication channel between them is secure. Moreover, A and C share a secret key, K. Please design a three-party authenticated key exchange protocol with forward secrecy using only symmetry-based encryption, cryptographic hash function, and Diffie-Hellman key agreement. (Note:The security feature of mutual authentication, session key exchange, and forward secrecy should be achieved among A and B).