Method and device for cryptographic processing of data

A device for cryptographic processing of first data, comprising a processor programmed to:

• store an initial value as a current value;
• implement a predetermined number of first steps, involving, during one of said first steps, an application of a first cryptographic algorithm to the first data in such a way as to obtain second data, and, during each of the other of said first steps, the application of the first cryptographic algorithm to the current value in such a way as to obtain a result and a storage of the result as the new current value;
• implement the predetermined number of second steps, involving, during one of said second steps, the application, to third data, of a second cryptographic algorithm that is the inverse of the first cryptographic algorithm in such a way as to obtain fourth data, and, during each of the other of said second steps, an application of the second cryptographic algorithm to the current value in such a way as to obtain another result and a storage of the other result as the new current value;
• verify the equality of the first data and the fourth data, and the equality of the current value and the initial value.