| 摘要 |
PROBLEM TO BE SOLVED: To provide an encrypting/decrypting method in which calculating cost is low, at least by using a common key. SOLUTION: The encrypting/decrypting method of the invention uses; a first device including a first private key and the common key, and a second device including a second private key and the common key. In the encrypting/decrypting method, a cipher which the first device encrypts is decrypted to a plain text by the second device. The method comprises: a first step in which the first device gives the second device a first cipher which is obtained by encrypting the plain text according to a predetermined formula using the second private key and the common key; a second step in which the second device gives the first device a second cipher which is obtained by encrypting the first cipher according to the predetermined formula using the second private key and the common key; a third step in which the first device gives the second device a third cipher which is obtained by encrypting the second cipher according to the predetermined formula using the first private key and the common key; and a fourth step in which the second device restores the plain text from the third cipher according to the predetermined formula using the second private key and the common key. COPYRIGHT: (C)2007,JPO&INPIT
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