Abstract: A cryptographic processing method comprises the following steps: obtaining a second number determined by adding to a first number the order of a finite group or a multiple of this order; determining a quotient and a remainder by dividing the second number by a random number; obtaining a third element equal to the combination of elements equal to a first element of the finite group and in number equal to the product of the quotient and the random number; obtaining a fourth element equal to the combination of elements equal to the first element and in number equal to the remainder; determining a second element by combining the third element and the fourth element.

Abstract: The invention proposes a novel type of infective countermeasure against fault injection attacks. Instead of determining the injected error before amplifying it, the novel countermeasure applies the same diffusion function to two intermediate ciphers obtained by executing a cryptographic operation on an input. The error is therefore amplified within the same intermediate ciphers, referred to as infective ciphers after diffusion. It is then possible to use diffusion functions which do not map the cipher 0 as an output equal to 0. A cipher recomposed from bits of undiffused ciphers is also generated. These infective and recomposed ciphers are XOR-combined to provide an output cipher. This approach makes it possible to adapt, by simple duplication of the pairs and associated specific diffusion functions, the protection offered by the countermeasure to a desired number of injected faults.

Abstract: A cryptographic processing method comprises the following steps: obtaining a second number determined by adding to a first number the order of a finite group or a multiple of this order; determining a quotient and a remainder by dividing the second number by a random number; obtaining a third element equal to the combination of elements equal to a first element of the finite group and in number equal to the product of the quotient and the random number; obtaining a fourth element equal to the combination of elements equal to the first element and in number equal to the remainder; determining a second element by combining the third element and the fourth element.

Abstract: A method for determining a first integrity sum including the following steps: determining a first masked item of data by application of an “exclusive OR” operation between a first item of data and a first data mask; —determining a second item of data by application to the first masked item of data of a first cryptographic function, the second item of data being masked by a second data mask; —determining a second integrity sum associated with the second item of data by application to the second item of data of a checksum function; and determining the first integrity sum by application of an “exclusive OR” operation between the second integrity sum and a third integrity sum associated with the second data mask. A computer program and an electronic entity are also described.

Abstract: A method for determining a first integrity sum including the following steps: determining a first masked item of data by application of an “exclusive OR” operation between a first item of data and a first data mask; —determining a second item of data by application to the first masked item of data of a first cryptographic function, the second item of data being masked by a second data mask; —determining a second integrity sum associated with the second item of data by application to the second item of data of a checksum function; and determining the first integrity sum by application of an “exclusive OR” operation between the second integrity sum and a third integrity sum associated with the second data mask. A computer program and an electronic entity are also described.