| 摘要 |
PROBLEM TO BE SOLVED: To carry out group encryption communication between computers of a plurality of users without communicating with a server. SOLUTION: When a computer 1-C transmits a request for subscription to a group to a computer 1-A (S202-3) when computers 1-A and 1-B carry out the group encryption communication, exchange keys are exchanged among the computers 1-A to 1-C (S210-1 and S210-3). The respective computers 1-A, 1-B and 1-C generate group secret keys based on received exchange keys (S211-1 to S211-3). Hereafter, the group encryption communication is carried out using the group secret keys. In the case of according to a Diffie-Hellman type key exchange system, the exchange keysαand Z of the computers 1-A, 1-C become gamod p and gzmod p, and the group secret keys calculated by the computers 1-A, 1-C become Zamod p,αzmod p, and become the same value as gazmod p. That is, it is possible to carry out group encryption communication using the group secret key without using the server. COPYRIGHT: (C)2007,JPO&INPIT
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