| 摘要 |
PROBLEM TO BE SOLVED: To reduce a processing time and communication costs for updating a key in cipher communication. SOLUTION: The user of the cipher communication first exchanges and shares a basic key (k) by a Diffie-Hellman key exchange system or the like. The size of the basic key (k) is kept larger than that of a cryptographic key. Cryptographic keys (g) are respectively separately generated from the basic key (k) according to the same one directional function. After the end of the communication, key updating is executed for the next cipher communication. Only by the first basic key exchange, an i-th cryptographic key g(k, i) is generated without performing communication for cryptographic key updating after that. Key updating can be executed after the end of communication and a waiting time and communication costs during communication for key updating can be reduced. Identity is also proved by enabling the generation of the next cryptographic key and a role as authentication can be obtained as well.
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