Method for distributing key using public key cryptographic technique and on-line updating of the public key

The invention relates to a method for the distribution of an encryption key and the online innovation of a public key, which comprises the steps that: (1) a first entity produces a temporary public and private key pair; (2) a communication conversation encryption key exists between the first entity and a second entity; (3) an encryption key distribution center locally stored is utilized to carry out the signature verification of the public key; (4) the second entity produces a temporary public and private key pair; (5) a encryption key response message is formed and returned to the second entity; (6) the encryption key distribution center locally stored is utilized to carry out the signature verification of the public key; (7) the communication conversation encryption key is utilized by the first entity and the second entity to serve as a conversation encryption key to carry out secret communication. The method proposes a method that safely distributes communication encryption key to each pair of entity, causes the encryption key to have PFS property and lowers the complexity of the encryption key management of the system, and also supports the online innovation function of a public key of the encryption key distribution center which is the trusted third party.