Patent ID: 8588407
Filing Date: 2013-11-19
Classification: G06F

Abstract:
1. A method for protecting a digital quantity over a first number of bits, in an algorithm executing at least one modular exponentiation of data by said quantity, successive iterations of different calculation steps, according to a state of a current bit of said quantity, comprising at least two multiplications, the method comprising performing, for each iteration, a same number of multiplications whatever the state of said current bit, said steps of each iteration comprising a test on the state of only said current bit to condition the operands of at least one of the multiplications, branching to a first multiplication or to a second multiplication according to the state of said current bit, and using intermediate results of all the multiplication steps of each iteration in calculating a final result, wherein for a number n of bits of said quantity, a first register for storing the final result is initialized with the unity value and said steps of each iteration of n iterations are: where S