| 摘要 |
PROBLEM TO BE SOLVED: To provide an encryption techniques, etc., which shorten the time required for decryption processing as far as possible while taking countermeasures against an illicit copying. SOLUTION: Data are subjected to encryption invariable in data length before and after the encryption in accordance with an encryption ratio for every data length. The encryption patterns of (a) encrypt only the one-third from the top and leave the remaining two-thirds as a plaintext. The encryption patterns of (b) successively apply three kinds of the encryption patterns P1 to P3 varying in the encryption ratios to the data. These patterns encrypt data size 50%, 25% and 75%, respectively from the top. The encryption patterns of (c) successively apply three kinds of the encryption patterns P11 to P13 further changed up to an encryption start position to the data. The contents of the patterns are that P11 encrypts a data size 50% from the top 25% position, P12 encrypts a data size 25% from the top 50% position and P13 encrypts a data size 75% from the top 0% position. COPYRIGHT: (C)2004,JPO |
