Patent ID: 8634551

Claim:
A cryptographic apparatus to carry out calculations according to an FI function including a first non-linear function S 9 and a second non-linear function S 7 , comprising: a read-only memory recording a first conversion table including, for each first input X of 9*n bits (n is an integer equal to or larger than 1), a value obtained by exclusively ORing a first value and an first output from said first non-linear function S 9 with respect to a first input X, wherein said first value is generated by shifting lower 7*n bits in said first output to left by 9*n bits; and a second conversion table including, for each second input Y of 7*n bits, a value obtained by exclusively ORing a second value and said second input Y, wherein said second value is generated by shifting a result of an exclusive OR of said second input Y and a second output from said second non-linear function S 7 with respect to a second input Y to left by 9*n bits; and an FI function calculation unit to carry out one calculation of an FI function by using, twice, said first conversion table recorded on said read-only memory and using, once, said second conversion table recorded on said read-only memory.