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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*/
#include "tomcrypt.h"
#ifdef LTC_MDH
/**
Check DH public key (INTERNAL ONLY, not part of public API)
@param key The key you wish to test
@return CRYPT_OK if successful
*/
int dh_check_pubkey(dh_key *key)
{
void *p_minus1;
ltc_mp_digit digit;
int i, digit_count, bits_set = 0, err;
LTC_ARGCHK(key != NULL);
if ((err = mp_init(&p_minus1)) != CRYPT_OK) {
return err;
}
/* avoid: y <= 1 OR y >= p-1 */
if ((err = mp_sub_d(key->prime, 1, p_minus1)) != CRYPT_OK) {
goto error;
}
if (mp_cmp(key->y, p_minus1) != LTC_MP_LT || mp_cmp_d(key->y, 1) != LTC_MP_GT) {
err = CRYPT_INVALID_ARG;
goto error;
}
/* public key must have more than one bit set */
digit_count = mp_get_digit_count(key->y);
for (i = 0; i < digit_count && bits_set < 2; i++) {
digit = mp_get_digit(key->y, i);
while (digit > 0) {
if (digit & 1) bits_set++;
digit >>= 1;
}
}
if (bits_set > 1) {
err = CRYPT_OK;
}
else {
err = CRYPT_INVALID_ARG;
}
error:
mp_clear(p_minus1);
return err;
}
#endif /* LTC_MDH */
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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