CIPHERING METHOD, CIPHERING DEVICE, RECORDING MEDIUM WHERE CIPHERING PROGRAM IS RECORDED

摘要

PROBLEM TO BE SOLVED: To enable a provable and safe ciphering process to be performed against an attack using impossible differentials. SOLUTION: An inverse element calculation part 10 receives an n-bit plaintext, and converts it into an inverse element on GF (2n). However, the inverse element of 0 is defined as 0. An exclusive-OR calculation part 120 calculates an exclusive-OR for every bit of n-bit key and the output of the inverse element calculation part 110. The inverse element calculation part 130 converts the output of the exclusive-OR calculation part 120 into an inverse element on GF (2n) and outputs it. However, the inverse element of 0 is defined as 0.