| 摘要 |
PURPOSE:To prevent reduction in data transmission efficiency from being caused by outputting a data cryptographic key from a common key and a time latch value, ciphering a communication plain text and outputting a data decoding key from the common key and the time latch to decode the received cryptographic key. CONSTITUTION:A trigger message generator 23 generating a trigger signal message when a communication session is started, a timer 17 giving data time information, a time latch 19 latching it by the trigger message, and a ciphering device 21 are provided to give the same data time information to two terminal equipments by the trigger signal message and the data cryptographic key is provided in common between two terminal equipments by using the common key KC. Thus, every time one communication session of the ciphering data communication is applied, the request of a data cryptographic key KS is not required to the key delivery center and the data transmission efficiency is not lowered.
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