| 摘要 |
PROBLEM TO BE SOLVED: To realize a high speed cipher/decipher conversion which is strong in decipher without increasing the repeating times of the conversion by providing a means which sets the shift number in bit string conversion processing for cipher so as to become specified value and sets the same in such a manner that the value of the shift number does not coincide with each other between continuously executed cipher operation processes. SOLUTION: An algorythm key is composed of addition values A1n-A3n (32 bit data) which is used for adding operation in adding operational parts 95, 96 and 98 and shift values S1n-S3n (1<=S1n-S3n<=31) which are used for left cyclic shift operation in cyclic shift operational parts 91-93. Therein, the shift values S1n-S3n are set in such a manner that all of the shift values are odd numbers or either one of S1n and S2n is 2 and the remaining two are odd numbers. Further, in transformed letter inverting and transforming parts of successive two steps, corresponding shift numbers are set so as not to coincide with each other. That is, the shift values are set so as to be S1i≠S1i+1, S2i≠S2i+1 and S3i≠S3i+1.
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