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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"
/**
@file dsa_verify_key.c
DSA implementation, verify a key, Tom St Denis
*/
#ifdef LTC_MDSA
/**
Validate a DSA key
Yeah, this function should've been called dsa_validate_key()
in the first place and for compat-reasons we keep it
as it was (for now).
@param key The key to validate
@param stat [out] Result of test, 1==valid, 0==invalid
@return CRYPT_OK if successful
*/
int dsa_verify_key(dsa_key *key, int *stat)
{
int err;
err = dsa_int_validate_primes(key, stat);
if (err != CRYPT_OK || *stat == 0) return err;
err = dsa_int_validate_pqg(key, stat);
if (err != CRYPT_OK || *stat == 0) return err;
return dsa_int_validate_xy(key, stat);
}
/**
Non-complex part (no primality testing) of the validation
of DSA params (p, q, g)
@param key The key to validate
@param stat [out] Result of test, 1==valid, 0==invalid
@return CRYPT_OK if successful
*/
int dsa_int_validate_pqg(dsa_key *key, int *stat)
{
void *tmp1, *tmp2;
int err;
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(stat != NULL);
*stat = 0;
/* check q-order */
if ( key->qord >= LTC_MDSA_MAX_GROUP || key->qord <= 15 ||
(unsigned long)key->qord >= mp_unsigned_bin_size(key->p) ||
(mp_unsigned_bin_size(key->p) - key->qord) >= LTC_MDSA_DELTA ) {
return CRYPT_OK;
}
/* FIPS 186-4 chapter 4.1: 1 < g < p */
if (mp_cmp_d(key->g, 1) != LTC_MP_GT || mp_cmp(key->g, key->p) != LTC_MP_LT) {
return CRYPT_OK;
}
if ((err = mp_init_multi(&tmp1, &tmp2, NULL)) != CRYPT_OK) { return err; }
/* FIPS 186-4 chapter 4.1: q is a divisor of (p - 1) */
if ((err = mp_sub_d(key->p, 1, tmp1)) != CRYPT_OK) { goto error; }
if ((err = mp_div(tmp1, key->q, tmp1, tmp2)) != CRYPT_OK) { goto error; }
if (mp_iszero(tmp2) != LTC_MP_YES) {
err = CRYPT_OK;
goto error;
}
/* FIPS 186-4 chapter 4.1: g is a generator of a subgroup of order q in
* the multiplicative group of GF(p) - so we make sure that g^q mod p = 1
*/
if ((err = mp_exptmod(key->g, key->q, key->p, tmp1)) != CRYPT_OK) { goto error; }
if (mp_cmp_d(tmp1, 1) != LTC_MP_EQ) {
err = CRYPT_OK;
goto error;
}
err = CRYPT_OK;
*stat = 1;
error:
mp_clear_multi(tmp2, tmp1, NULL);
return err;
}
/**
Primality testing of DSA params p and q
@param key The key to validate
@param stat [out] Result of test, 1==valid, 0==invalid
@return CRYPT_OK if successful
*/
int dsa_int_validate_primes(dsa_key *key, int *stat)
{
int err, res;
*stat = 0;
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(stat != NULL);
/* key->q prime? */
if ((err = mp_prime_is_prime(key->q, LTC_MILLER_RABIN_REPS, &res)) != CRYPT_OK) {
return err;
}
if (res == LTC_MP_NO) {
return CRYPT_OK;
}
/* key->p prime? */
if ((err = mp_prime_is_prime(key->p, LTC_MILLER_RABIN_REPS, &res)) != CRYPT_OK) {
return err;
}
if (res == LTC_MP_NO) {
return CRYPT_OK;
}
*stat = 1;
return CRYPT_OK;
}
/**
Validation of a DSA key (x and y values)
@param key The key to validate
@param stat [out] Result of test, 1==valid, 0==invalid
@return CRYPT_OK if successful
*/
int dsa_int_validate_xy(dsa_key *key, int *stat)
{
void *tmp;
int err;
*stat = 0;
LTC_ARGCHK(key != NULL);
LTC_ARGCHK(stat != NULL);
/* 1 < y < p-1 */
if ((err = mp_init(&tmp)) != CRYPT_OK) {
return err;
}
if ((err = mp_sub_d(key->p, 1, tmp)) != CRYPT_OK) {
goto error;
}
if (mp_cmp_d(key->y, 1) != LTC_MP_GT || mp_cmp(key->y, tmp) != LTC_MP_LT) {
err = CRYPT_OK;
goto error;
}
if (key->type == PK_PRIVATE) {
/* FIPS 186-4 chapter 4.1: 0 < x < q */
if (mp_cmp_d(key->x, 0) != LTC_MP_GT || mp_cmp(key->x, key->q) != LTC_MP_LT) {
err = CRYPT_OK;
goto error;
}
/* FIPS 186-4 chapter 4.1: y = g^x mod p */
if ((err = mp_exptmod(key->g, key->x, key->p, tmp)) != CRYPT_OK) {
goto error;
}
if (mp_cmp(tmp, key->y) != LTC_MP_EQ) {
err = CRYPT_OK;
goto error;
}
}
else {
/* with just a public key we cannot test y = g^x mod p therefore we
* only test that y^q mod p = 1, which makes sure y is in g^x mod p
*/
if ((err = mp_exptmod(key->y, key->q, key->p, tmp)) != CRYPT_OK) {
goto error;
}
if (mp_cmp_d(tmp, 1) != LTC_MP_EQ) {
err = CRYPT_OK;
goto error;
}
}
err = CRYPT_OK;
*stat = 1;
error:
mp_clear(tmp);
return err;
}
#endif
/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */
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