Patent ID: 7558386

Claim:
A countermeasure method in an electronic component using a cryptographic algorithm that comprises multiple successive rounds of operation with a secret key, wherein at least one of said rounds is implemented with a first manipulation means for supplying an output data item from an input data item, and the output data item is manipulated by means of instructions, and wherein at least one other round of said algorithm is implemented with other manipulation means for supplying output data, so that the output data item is unpredictable, said other manipulation means being obtained from said first manipulation means by performing an exclusive OR operation on said first manipulation means with a random value, and wherein each round using manipulation means for supplying an output data item from an input data item, the output data item being manipulated by instructions in at least a first three rounds and at least a last three rounds, and wherein said method includes the steps of forming a first group comprising at least the first three rounds and another group comprising at least the last three rounds, and implementing the first group and the last group with an execution sequence using the other manipulation means in at least some rounds.