| 摘要 |
PROBLEM TO BE SOLVED: To efficiently broadcast an electronic mail containing an enciphered data. SOLUTION: A personal computer PC1 generates a session key when receiving from a user an indication that the same data is transmitted to plural addresses by the electronic mail (S105), and enciphers the data using the generated session key (S106). A common key is generated using a public key generated based on each electronic mail address of the addresses and a private key acquired preliminarily from a center (S107), and enciphers the session key using the generated common key (S108). The electronic mail containing the enciphered data and the session key is transmitted to the respective addresses (S110).
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