| 摘要 |
PROBLEM TO BE SOLVED: To provide a method, system, etc., of forming intricately changed keys form source keys without increasing the burden for packaging. SOLUTION: An F function 10 which is the same as the function for encryption is used in forming the key Ki; key formation data ri to ri+3 are stored into a memory 40 and the results of the exclusive OR operation of the data ri and ri+1 are inputted to the F function. A series qi of parameters is used as the key to be used in the F function and the outputs of the F function are determined as the keys of respective rounds. The outputs are subjected to the exclusive OR operation with the source keys Ka and Kb and the results thereof are used as the next key formation data.
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