Method for cryptographic processing of first data (M; C), comprising the following steps: - storage of an initial value as a current value; - implementation of a predetermined number of first steps (E14, E16; E66, E68), one (E14; E66) of said first steps involving the obtaining of second data by applying a first cryptographic algorithm (F K; F I) to the first data (M; C), the other ones (E16; E68) of said first steps each involving the obtaining of a result by applying the first cryptographic algorithm (F K; F I) to the current value and the storage of the result as the new current value; - implementation of the predetermined number of second steps (E28, E30; E86, E88), one (E28; E86) of said second steps involving the obtaining of fourth data (C') by applying, to third data (C; C'), a second cryptographic algorithm (F K -1; F P+1-I -1) that is the inverse of the first cryptographic algorithm (F K; F I), the other ones (E30; E88) of said second steps each involving the obtaining of another result by applying the second cryptographic algorithm (F K -1; F P+1-I -1) to the current value and the storage of the other result as the new current value; - verification (E36; E98, E100) of the equality of the first data (M; C) and the fourth data (C'), and of the equality of the current value and the initial value, wherein the third data is the second data, or wherein the method further comprises the following steps: - obtaining fifth data by applying a third cryptographic algorithm to the second data; - obtaining sixth data by applying a fourth cryptographic algorithm to the fifth data; - obtaining seventh data by applying, to the sixth data, a fifth cryptographic algorithm that is the inverse of the fourth cryptographic algorithm; - obtaining the third data by applying, to the seventh data, a sixth cryptographic algorithm that is the inverse of the third cryptographic algorithm, or wherein the method comprises the following steps, the second data being used as current data: - implementation of a second predetermined number of third steps each involving the obtaining of a result by applying the first cryptographic algorithm to the current data and the storage of the result as the new current data; - implementation of the second predetermined number of fourth steps each involving the obtaining of another result by applying the second cryptographic algorithm to the current data and the storage of the other result as the new current data, said third data being the current data after implementation of said fourth steps. - storage of an initial value as a current value; - implementation of a predetermined number of first steps (E14, E16; E66, E68), one (E14; E66) of said first steps involving the obtaining of second data by applying a first cryptographic algorithm (F K; F I) to the first data (M; C), the other ones (E16; E68) of said first steps each involving the obtaining of a result by applying the first cryptographic algorithm (F K; F I) to the current value and the storage of the result as the new current value; - implementation of the predetermined number of second steps (E28, E30; E86, E88), one (E28; E86) of said second steps involving the obtaining of fourth data (C') by applying, to third data (C; C'), a second cryptographic algorithm (F K -1; F P+1-I -1) that is the inverse of the first cryptographic algorithm (F K; F I), the other ones (E30; E88) of said second steps each involving the obtaining of another result by applying the second cryptographic algorithm (F K -1; F P+1-I -1) to the current value and the storage of the other result as the new current value; - verification (E36; E98, E100) of the equality of the first data (M; C) and the fourth data (C'), and of the equality of the current value and the initial value, - obtaining fifth data by applying a third cryptographic algorithm to the second data; - obtaining sixth data by applying a fourth cryptographic algorithm to the fifth data; - obtaining seventh data by applying, to the sixth data, a fifth cryptographic algorithm that is the inverse of the fourth cryptographic algorithm; - obtaining the third data by applying, to the seventh data, a sixth cryptographic algorithm that is the inverse of the third cryptographic algorithm, - implementation of a second predetermined number of third steps each involving the obtaining of a result by applying the first cryptographic algorithm to the current data and the storage of the result as the new current data; - implementation of the second predetermined number of fourth steps each involving the obtaining of another result by applying the second cryptographic algorithm to the current data and the storage of the other result as the new current data,