| 摘要 |
PROBLEM TO BE SOLVED: To reduce the risk of information leak by shortening a time to be required for encryption and data concealing processing. SOLUTION: A server device 1 generates a primary cipher text 103 by applying an exclusive OR operation to a plain text 101 and a first stream encryption key 102 by bit so as to primarily encrypt the plain text; generates a bit string 104 by applying an exclusive OR operation to the first stream encryption key and the second stream encryption key by bit, operating the bit string and the primary cipher text by bit, so as to secondarily encrypt the primary cipher text; and then transmits a secondary cipher text 105 generated by secondary encryption to a user device 2. The user device applies an exclusive OR operation to the secondary cipher text and a second stream encryption key 106 by bit, so as to decrypt the secondary cipher text. The different keys are used simultaneously for decryption and encryption. Consequently, high-speed re-encryption processing is attained, and the data are not restored to the plain text in re-encryption, so that the risk of the information leak is reduced. COPYRIGHT: (C)2008,JPO&INPIT
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