16. The system according to claim 15 , in which the extraction means comprise means forming an error correction code, reading means, processing means configured for determining said value of the digital information, and control means configured for disabling the means forming an error correction code and enabling the reading means for reading each modified digital word, the processing means comprising comparison means configured for carrying out a comparison of the bits of each modified digital word with the bits of each corresponding initial word, the result of each comparison supplying the position of the modified bit in the corresponding digital word.
17. The system according to claim 16 , in which the control means are further configured for enabling the means forming an error correction code and enabling the reading means for reading each modified digital word, this read operation supplying the values of the bits of each initial digital word.