A method, system and equipment for key distribution are disclosed. During the course of computing a shared key Kab between a client node and a third party equipment, a serial number is introduced into keying materials to compute the Kab, instead of just using constant parameter, thus once the Kab is leaked, the Kab can be simply and duly updated by updating the variable parameter, and hence the security of message transmission is improved. Furthermore, in the implementations, methods for security protection and security verification for message are used, so as to effectively prevent threats to message security such as message forgery or replay attack, and hence further improve the security of message transmission.