Patent ID: 7496758
Filing Date: 2009-02-24
Classification: G06F

Abstract:
1. A method for protecting an exponentiation calculation by means of the Chinese remainder theorem using two prime numbers forming auxiliary modules for calculating auxiliary quantities which may be joined to calculate a modular exponentiation for a module equal to the product of the auxiliary quantities, wherein the exponentiation calculation is performed within a cryptographic algorithm for an encryption of a message, a decryption of a message, a signature generation from a message or a signature verification calculation from a message, the method comprising: calculating the first auxiliary quantity using the first prime number as the module and using the message; calculating the second auxiliary quantity using the second prime number as the module and using the message; combining the first auxiliary quantity and the second auxiliary quantity using a combination algorithm to obtain a result of the exponentiation calculation; following the combining step, verifying the result of the exponentiation calculation by means of a verifying algorithm, which differs from the combination algorithm, using the first prime number and/or the second prime number, the verifying algorithm providing a predetermined result if the combining step has been performed correctly; and if the verifying step shows that the verifying algorithm provides a result other than the predetermined result, suppressing an output of the result of the exponentiation calculation.