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AssigneeGemalto SA
InventorsMathieu Ciet, Benoit Feix
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A cryptographic method carries out a modular exponentiation of the type C=A<B1> mod N, where A is an operand, B1 is a first exponent, N is a modulus and C is a result. The method includes the steps of masking the operand A by a number s, carrying out a modular exponentiation of the masked operand by the exponent B1, and demasking the result of the exponentiation, by removing a contribution from the random number s from the result of the exponentiation. During the step of masking the operand A, the operand A is multiplied by a parameter of the form K<s.B2>, where K is a constant and B2 is a second exponent such that B1.B2=1 mod N. The method is implemented preferably by using a Montgomery multiplier. The preferred choice for the constant K is K=2p, p being an integer lying between 0 and n, n being an upper bound of the size of the modulus N and conventionally depending on the choice of implementation of the Montgomery multiplication.
Cryptographic method during which, in order to carry out a modular exponentiation of type C=AB1 mod N, where A is an operand comprising a message on which a cryptographic operation is being performed, B1 is a first exponent, N is a modulus, and C is a result, comprising the following steps:
A cryptoprocessor device comprising a Montgomery multiplier configured to implement a method to carry out a modular exponentiation of type C=AB1 mod N, where A is an operand comprising a message on which a cryptographic operation is being performed, B1 is a first exponent, N is a modulus, and C is a result, comprising the following steps:
Dependencies are inferred from the claim text.