Gemalto Sa

Gemplus

Christophe Clavier

Jean-Sébastien Coron

Olivier Benoit

In an electronic component using a secret key cryptographic algorithm, one operation utilizes a first table for supplying output data from input data. The output data, and/or derived data, is manipulated by critical instructions. A countermeasure method involves the use of other tables such that the output data and the derived data are unpredictable. The other tables are obtained from the first table by an exclusive-OR operation with a random value, or a derived random value, on one and/or the other of the input and output data of the first table.

Countermeasure method in an electronic component using a secret key cryptographic algorithm

The invention concerns a countermeasure method in an electronic component using a secret key K cryptographic algorithm with sixteen computing cycles to supply an encrypted message (C) from an input message (M), each cycle using first means TCto supply an output information from an input information, Said method consists in applying by selection a sequence with the first means or another sequence with other means TC, TCto a group Gcomprising the first three cycles at least and another group Gcomprising the last three cycles at least. Whatever the sequence, the output result of the last cycle of each group is the same for the same input message (M).

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Gémenos, France

Christophe Clavier