Patent ID: 7778413

Claim:
A cryptographic system for encrypting input data in accordance with an encryption algorithm having a repeated-round structure, comprising: an encryption unit updating and storing encrypted data in accordance with the encryption algorithm in each given round, and outputting the encrypted data after executing encryption for a given number of rounds, and a compensation unit generating and storing compensation data so that a sum of a Hamming distance for the updated and stored encrypted data and a Hamming distance of the compensation data is maintained at a constant value, wherein the compensation unit includes: a compensation data generating unit generating the compensation data based on the number of rounds performed, and a compensation register storing the compensation data in response to a clock signal, wherein the compensation data generating unit includes: an inverting unit inverting the encrypted data, a first selecting unit selecting and outputting one of the encrypted data and inverted data of the encrypted data, based on the number of rounds performed, and a second selecting unit selecting and outputting one of data output from the first selecting unit and the input data based on the number of rounds performed.