/**
* checks a message authenticity
*
* The function computes CMAC of the given plain text and compares
* it against cmac4. Returns 1 if CMACs matches.
*
* @param skey 128-bit session key
* @param cmac4: points to CMAC message part, i.e. 4 bytes CMAC
* @param plain: plain text to be CMACked and checked against
* @param len: length of plain text in bytes
*/
int macan_check_cmac(struct macan_ctx *ctx, struct macan_key *skey, const uint8_t *cmac4, uint8_t *plain, uint8_t *fill_time, unsigned len)
{
uint8_t cmac[16];
uint64_t time;
int32_t *ftime = (int32_t *)fill_time;
int i;
if (!fill_time) {
macan_aes_cmac(skey, len, cmac, plain);
/* add memcmp instead of memchk */
return memchk(cmac4, cmac, 4);
}
time = macan_get_time(ctx);
for (i = -1; i <= 1; i++) {
*ftime = htole32((int)time + i);
macan_aes_cmac(skey, len, cmac, plain);
if (memcmp(cmac4, cmac, 4) == 0) {
return 1;
}
}
return 0;
}
/**
* checks a message authenticity
*
* The function computes CMAC of the given plain text and compares
* it against cmac4. Returns 1 if CMACs matches.
*
* @param skey 128-bit session key
* @param cmac4: points to CMAC message part, i.e. 4 bytes CMAC
* @param plain: plain text to be CMACked and checked against
* @param len: length of plain text in bytes
*/
int macan_check_cmac(struct macan_ctx *ctx, struct macan_key *skey, const uint8_t *cmac4,
uint8_t *plain, int time_index, unsigned len)
{
uint8_t cmac[16];
uint32_t *time_ptr;
if (time_index < 0 || (unsigned)time_index > len - sizeof(*time_ptr)) {
macan_aes_cmac(skey, len, cmac, plain);
/* add memcmp instead of memchk */
return memchk(cmac4, cmac, 4);
}
uint32_t time = (uint32_t)macan_get_time(ctx);
int delta_t;
time_ptr = (uint32_t *)&plain[time_index];
for (delta_t = -1; delta_t <= 1; delta_t++) {
*time_ptr = htole32(time + (uint32_t)delta_t);
macan_aes_cmac(skey, len, cmac, plain);
if (memcmp(cmac4, cmac, 4) == 0) {
return 1;
}
}
return 0;
}
/**
* sign() - signs a message with CMAC
* @skey: 128-bit session key
* @cmac4: 4 bytes of the CMAC signature will be written to
* @plain: a plain text to sign
* @len: length of the plain text
*/
void macan_sign(struct macan_key *skey, uint8_t *cmac4, uint8_t *plain, unsigned len)
{
uint8_t cmac[16];
macan_aes_cmac(skey, len, cmac, plain);
memcpy(cmac4, cmac, 4);
}
