Patent ID: 7471791

Claim:
A countermeasure method in an electronic component that implements the DES cryptographic algorithm in which multiple rounds of calculation are performed on input data, said DES cryptographic algorithm being divided into stages including a plurality of successive rounds, wherein each round of calculation in the DES cryptographic algorithm includes at least the following operations: a first permutation of data; manipulation of the permuted data by a secret key; a table look-up operation based on the manipulated data; and a second permutation of data; wherein, for some, but less than all, of said stages of said DES cryptographic algorithm, at least one of said first and second permutations of data comprises the following steps: selecting a first random value having the same size as the data being permuted, performing an exclusive-OR operation between the data being permuted and the first random value to generate a second random value, executing said permutation operation on each of the first and second random values, to generate respective first and second random results, and performing an exclusive-OR operation between said first and second random results to produce a final permuted result.