| 摘要 |
PROBLEM TO BE SOLVED: To provide a frame work for ciphering/deciphering which supports a function to transfer the decoding right of a message. SOLUTION: An original message to be transmitted to a recipient is coded by a public, non-exchangeable method. The method includes a step in which a ciphered message of an original message that is ciphered by a public key corresponding to the recipient is obtained, a step in which a public substitute key in which the secret key of the recipient is very difficult to be deciphered by computations on the basis of the secret key of the recipient, and a step in which the public substitute key is applied to convert the ciphered message to a converted message that can be decoded by the recipient by employing the secret key of the recipient and a piece of information selected from public information that is arbitrarily usable. |
