crypto/dh/dh_check.c

/* crypto/dh/dh_check.c */
/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
 * All rights reserved.
 *
 * This package is an SSL implementation written
 * by Eric Young (eay@cryptsoft.com).
 * The implementation was written so as to conform with Netscapes SSL.
 *
 * This library is free for commercial and non-commercial use as long as
 * the following conditions are aheared to.  The following conditions
 * apply to all code found in this distribution, be it the RC4, RSA,
 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
 * included with this distribution is covered by the same copyright terms
 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
 *
 * Copyright remains Eric Young's, and as such any Copyright notices in
 * the code are not to be removed.
 * If this package is used in a product, Eric Young should be given attribution
 * as the author of the parts of the library used.
 * This can be in the form of a textual message at program startup or
 * in documentation (online or textual) provided with the package.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *    "This product includes cryptographic software written by
 *     Eric Young (eay@cryptsoft.com)"
 *    The word 'cryptographic' can be left out if the rouines from the library
 *    being used are not cryptographic related :-).
 * 4. If you include any Windows specific code (or a derivative thereof) from
 *    the apps directory (application code) you must include an acknowledgement:
 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
 *
 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 * The licence and distribution terms for any publically available version or
 * derivative of this code cannot be changed.  i.e. this code cannot simply be
 * copied and put under another distribution licence
 * [including the GNU Public Licence.]
 */

#include <stdio.h>
#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/dh.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;
    }
#if 0
    else if (BN_is_word(dh->g, DH_GENERATOR_3)) {
        l = BN_mod_word(dh->p, 12);
        if (l != 5)
            *ret |= DH_NOT_SUITABLE_GENERATOR;
    }
#endif
    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 *q = NULL;

    *ret = 0;
    q = BN_new();
    if (q == NULL)
        goto err;
    BN_set_word(q, 1);
    if (BN_cmp(pub_key, q) <= 0)
        *ret |= DH_CHECK_PUBKEY_TOO_SMALL;
    BN_copy(q, dh->p);
    BN_sub_word(q, 1);
    if (BN_cmp(pub_key, q) >= 0)
        *ret |= DH_CHECK_PUBKEY_TOO_LARGE;

    ok = 1;
 err:
    if (q != NULL)
        BN_free(q);
    return (ok);
}