| 摘要 |
PROBLEM TO BE SOLVED: To provide a key escrow system that can prevent escape of escrow at a low cost, allow a criminal investigation agency to intercept communication quickly as required and prevent limitless interception. SOLUTION: A control station 2 decides a group configuration in response to a request from a terminal 5, prepares one idle terminal 8 with respect to one group, and stores it. A base station 3 allows group terminals including the idle terminal 8 to generate a group key by the BD method. When the criminal investigation agency 6 intercepts communication, the control station 2 rents the idle terminal 8 to the criminal investigation agency 6. When the interception permission period is finished, the control station 2 excludes the idle terminal 8 and delivers a new group key to the group memberships. Even when the group configuration is dynamically subject to change, the communication of the group in which the criminal investigation object terminal is included can surely be intercepted only for the permitted period.
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