Files
Momentum-Firmware/lib/nfc/protocols/mrtd_helpers.c
Chris van Marle 0871d274eb MRTD add helper functions:
- Check digit
- KMRZ
2022-10-11 22:13:02 +02:00

71 lines
2.0 KiB
C

#include "mrtd_helpers.h"
uint8_t mrtd_bac_check_digit(const uint8_t* input, const size_t length) {
const size_t num_weights = 3;
uint8_t weights[] = {7, 3, 1};
uint8_t check_digit = 0;
uint8_t idx;
for(size_t i=0; i<length; ++i) {
uint8_t c = input[i];
if(c >= 'A' && c <= 'Z') {
idx = c - 'A' + 10;
} else if(c >= 'a' && c <= 'z') {
idx = c - 'a' + 10;
} else if(c >= '0' && c <= '9') {
idx = c - '0';
} else {
idx = 0;
}
check_digit = (check_digit + idx * weights[i%num_weights]) % 10;
}
return check_digit;
}
void mrtd_print_date(uint8_t* output, MrtdDate* date) {
output[0] = (date->year / 10) + '0';
output[1] = (date->year % 10) + '0';
output[2] = (date->month / 10) + '0';
output[3] = (date->month % 10) + '0';
output[4] = (date->day / 10) + '0';
output[5] = (date->day % 10) + '0';
}
// Safe size: MRTD_DOCNR_MAX_LENGTH + 1 (CD) + 6 (DOB) + 1 (CD) + 6 (DOE) + 1 (CD) + 1 (0x00)
// Test with:
// - DOCNR of size 9
// - DOCNR of size <9
// - DOCNR of size >9
// - DOCNR of size MRTD_DOCNR_MAX_LENGTH
bool mrtd_bac_get_kmrz(MrtdAuthData* auth, uint8_t* output, size_t output_size) {
size_t idx = 0;
size_t docnr_length = strlen(auth->doc_number);
size_t cd_idx = 0;
if(output_size < docnr_length + 16) {
return false;
}
cd_idx = idx;
memcpy(output+idx, auth->doc_number, docnr_length);
idx += docnr_length;
if(docnr_length < 9) {
memset(output+idx, '<', 9-docnr_length);
idx += 9-docnr_length;
}
output[idx++] = mrtd_bac_check_digit(output+cd_idx, docnr_length) + '0';
cd_idx = idx;
mrtd_print_date(output+idx, &auth->birth_date);
idx += 6;
output[idx++] = mrtd_bac_check_digit(output+cd_idx, 6) + '0';
cd_idx = idx;
mrtd_print_date(output+idx, &auth->expiry_date);
idx += 6;
output[idx++] = mrtd_bac_check_digit(output+cd_idx, 6) + '0';
output[idx++] = '\x00';
return true;
}