A local copy of OpenSSL from GitHub
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/*
* Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include "dh_locl.h"
/*-
* Check that p is a safe prime and
* if g is 2, 3 or 5, check that it is a suitable generator
* where
* for 2, p mod 24 == 11
* for 3, p mod 12 == 5
* for 5, p mod 10 == 3 or 7
* should hold.
*/
int DH_check(const DH *dh, int *ret)
{
int ok = 0;
BN_CTX *ctx = NULL;
BN_ULONG l;
BIGNUM *t1 = NULL, *t2 = NULL;
*ret = 0;
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
BN_CTX_start(ctx);
t1 = BN_CTX_get(ctx);
if (t1 == NULL)
goto err;
t2 = BN_CTX_get(ctx);
if (t2 == NULL)
goto err;
if (dh->q) {
if (BN_cmp(dh->g, BN_value_one()) <= 0)
*ret |= DH_NOT_SUITABLE_GENERATOR;
else if (BN_cmp(dh->g, dh->p) >= 0)
*ret |= DH_NOT_SUITABLE_GENERATOR;
else {
/* Check g^q == 1 mod p */
if (!BN_mod_exp(t1, dh->g, dh->q, dh->p, ctx))
goto err;
if (!BN_is_one(t1))
*ret |= DH_NOT_SUITABLE_GENERATOR;
}
if (!BN_is_prime_ex(dh->q, BN_prime_checks, ctx, NULL))
*ret |= DH_CHECK_Q_NOT_PRIME;
/* Check p == 1 mod q i.e. q divides p - 1 */
if (!BN_div(t1, t2, dh->p, dh->q, ctx))
goto err;
if (!BN_is_one(t2))
*ret |= DH_CHECK_INVALID_Q_VALUE;
if (dh->j && BN_cmp(dh->j, t1))
*ret |= DH_CHECK_INVALID_J_VALUE;
} else if (BN_is_word(dh->g, DH_GENERATOR_2)) {
l = BN_mod_word(dh->p, 24);
if (l != 11)
*ret |= DH_NOT_SUITABLE_GENERATOR;
} else if (BN_is_word(dh->g, DH_GENERATOR_5)) {
l = BN_mod_word(dh->p, 10);
if ((l != 3) && (l != 7))
*ret |= DH_NOT_SUITABLE_GENERATOR;
} else
*ret |= DH_UNABLE_TO_CHECK_GENERATOR;
if (!BN_is_prime_ex(dh->p, BN_prime_checks, ctx, NULL))
*ret |= DH_CHECK_P_NOT_PRIME;
else if (!dh->q) {
if (!BN_rshift1(t1, dh->p))
goto err;
if (!BN_is_prime_ex(t1, BN_prime_checks, ctx, NULL))
*ret |= DH_CHECK_P_NOT_SAFE_PRIME;
}
ok = 1;
err:
if (ctx != NULL) {
BN_CTX_end(ctx);
BN_CTX_free(ctx);
}
return (ok);
}
int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
{
int ok = 0;
BIGNUM *tmp = NULL;
BN_CTX *ctx = NULL;
*ret = 0;
ctx = BN_CTX_new();
if (ctx == NULL)
goto err;
BN_CTX_start(ctx);
tmp = BN_CTX_get(ctx);
if (tmp == NULL || !BN_set_word(tmp, 1))
goto err;
if (BN_cmp(pub_key, tmp) <= 0)
*ret |= DH_CHECK_PUBKEY_TOO_SMALL;
if (BN_copy(tmp, dh->p) == NULL || !BN_sub_word(tmp, 1))
goto err;
if (BN_cmp(pub_key, tmp) >= 0)
*ret |= DH_CHECK_PUBKEY_TOO_LARGE;
if (dh->q != NULL) {
/* Check pub_key^q == 1 mod p */
if (!BN_mod_exp(tmp, pub_key, dh->q, dh->p, ctx))
goto err;
if (!BN_is_one(tmp))
*ret |= DH_CHECK_PUBKEY_INVALID;
}
ok = 1;
err:
if (ctx != NULL) {
BN_CTX_end(ctx);
BN_CTX_free(ctx);
}
return (ok);
}