Method and device for secured writing of data in rewritable memory, for use in microelectronics and chip cards

摘要

The defined memory comprises a cyclic file containing m recordings organized in a loop, where m is in the range from 1 to n+1, and each recording comprises a rank, an integrity indicator having good and bad states, and a data value (step 2). The recordings of rank 1 to n are accessible, while the recording of rank n+1 is hidden to the user. In the presence of data, the cyclic file is selected (step 4). The device comprises means for searching the current recording having the higher rank m=n+1 (step 6), and for verifying the state of its integrity indicator (step 8). In the case of bad integrity indicator, the datum is written in the current recording of rank m=n+1 (step 10), and in the case of success of writing test (step 12) the rank of current recording is incremented by one unit m=n+1+1 becoming 1 which remains hidden, leaving accessible the recordings of rank from 2 to n+1 (step 14), while in the case of failure no modification is made to the rank of current recording m=n+1 which remains hidden, and the recordings of rank from 1 to n remain accessible (step 16). In the case of good integrity indicator, the datum is written in the recording of next rank m=n+1+1 becoming 1 (step 18), and in the case of success of writing test (step 20) the rank of recording is incremented by one unit which remains hidden, leaving the recordings of rank from 3 to n+2 accessible (step 22), while in the case of failure no modification is made to the rank of current recording m=n+2 which remains hidden, leaving the recordings of rank from 2 to n+1 accessible (step 24). The method also comprises a step of memory personalization which includes, in the presence of a recording of length x octets, the creation of recordings of size x+3 supplementary octets, where the supplementary octets remain hidden and affect the integrity indicator and the rank of recordings so that the writing procedure accepts only recordings whose size x+3 is less than or equal to the size of modulo memory page. The device is incorporated in a microelectronic component with rewritable memory.