Secure message exchange protocol

In the two and three Security Packet Exchange Protocols, one party is responsible for the "starting" role, and the other party is responsible for the "responding" role. The "Security Proxy" for starting user operations is considered as "starter", and the "responder" for responding to user operations ".
In the secure message exchange protocol, when an asymmetric (public) Key algorithm is used, it can be assumed that each entity (A, B) has A public key/private key pair. When used for encryption, Ka indicates the public part of a's asymmetric key. In digital signature, Ka indicates the private part of A's asymmetric key. The situation for entity B is similar. When symmetric (private) key algorithms are used, assume that the identified entity A and entity B share two one-way secret keys Ka and Kb or A single secret key Ka = Kb.
Security negotiation is completed by using parameters in the three-way exchange protocol. Negotiation is required to support flexibility in the architecture. This flexibility allows executors and users to select cryptographic algorithms and protocols they prefer. In the first process, the starter provides a security service directory and connection parameters (such as algorithm type, key length, and specific algorithm parameters for public keys ). In the second process, the responder should answer the question according to the service directory and connection parameters. If the initiator is consistent with the responder, the Protocol is executed and both parties use the parameters included in the response from the service and responder. Otherwise, the protocol and Connection Request fail.