| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the need for a group key to secure confidentiality of a multiple address message in group communication for mobile communication, where the configuration of groups is always changing. SOLUTION: In the case of making group communication from a terminal A to terminals B, C in a group (a) consisting of the terminals A, B, C, a message is divided in the unit of transmission and the message is encrypted by a common encryption key different in each transmission unit. The common encryption key is encrypted by a public encryption key of the terminals A, B. The encrypted message and plural common encryption keys which are encrypted for each of the terminals B, C are transmitted all together to the terminal B, C through multiple address transmission. Each of the reception terminal B, C decodes the common encryption key by the use of a decoding key of a public key and decodes the message by the use of the decoded common encryption key. Since other terminals cannot decode the common encryption key and cannot use common encryption keys with different transmission unit, confidentiality of the message is ensured. In the case of sending from the terminal B (c) and sending from the terminal C (b), the processing above is applied similarly. Since a public key corresponding to each terminal is used and no group key is required, the secrecy confidentiality of group communication is ensured by having merely to store the decoded key of the public key confidentially.
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