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: 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 transforming an input byte into an output byte comprises the following steps: converting a plurality of words, each comprising at least one bit of the input byte, into input cryptograms by application, to each of said words, of a homomorphic encryption function from a first group to a second group provided with an operation; obtaining output cryptograms as a function of the input cryptograms, this obtaining step including at least one processing during which said operation is applied to two intermediate cryptograms, this processing producing a cryptogram that is an image by the homomorphic encryption function of a word including a Boolean logic combination of two bits comprised respectively in two words that are arguments, for the homomorphic encryption function, of said two intermediate cryptograms; determining bits of the output byte by applying respectively to the output cryptograms, an inverse function of the homomorphic encryption function.