Patent ID: 8065735

Claim:
A method for performing a cryptographic operation on data in an electronic device with a key represented as a plurality of components (k t−1 , . . . , k 0 ) each having a first or second component value, said electronic device having at least one memory comprising at least one first register and a second register, said first register storing a first register value, said second register storing a second register value said method comprising the following steps: allocating to said first register a first initial register value as a first register value; allocating to said second register a second initial register value as a second register value, said second initial register value corresponding to the data on which the cryptographic operation is being performed; carrying out an iteration on said plurality of components of said representation, said iteration comprising the steps of, for each (k i ) of the components of said key: when said component (k i ) is equal to said first component value, calculating a first calculation value equal to the double of said first register value added to said second register value; and allocating said first calculation value to said first register as the first register value; when said component (k i ) is equal to said second component value, calculating a second calculation value equal to the double of said second register value added to said first register value; and allocating said second calculation value to said second register, as the second register value; following said iteration, returning at least one register value from said first register value and said second register value as the cryptographically processed data.