crypto/libressl/crypto/dh/dh_check.c

   1 /* $OpenBSD: dh_check.c,v 1.15 2015/02/07 13:19:15 doug Exp $ */
   2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
   3  * All rights reserved.
   4  *
   5  * This package is an SSL implementation written
   6  * by Eric Young (eay@cryptsoft.com).
   7  * The implementation was written so as to conform with Netscapes SSL.
   8  *
   9  * This library is free for commercial and non-commercial use as long as
  10  * the following conditions are aheared to.  The following conditions
  11  * apply to all code found in this distribution, be it the RC4, RSA,
  12  * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
  13  * included with this distribution is covered by the same copyright terms
  14  * except that the holder is Tim Hudson (tjh@cryptsoft.com).
  15  *
  16  * Copyright remains Eric Young's, and as such any Copyright notices in
  17  * the code are not to be removed.
  18  * If this package is used in a product, Eric Young should be given attribution
  19  * as the author of the parts of the library used.
  20  * This can be in the form of a textual message at program startup or
  21  * in documentation (online or textual) provided with the package.
  22  *
  23  * Redistribution and use in source and binary forms, with or without
  24  * modification, are permitted provided that the following conditions
  25  * are met:
  26  * 1. Redistributions of source code must retain the copyright
  27  *    notice, this list of conditions and the following disclaimer.
  28  * 2. Redistributions in binary form must reproduce the above copyright
  29  *    notice, this list of conditions and the following disclaimer in the
  30  *    documentation and/or other materials provided with the distribution.
  31  * 3. All advertising materials mentioning features or use of this software
  32  *    must display the following acknowledgement:
  33  *    "This product includes cryptographic software written by
  34  *     Eric Young (eay@cryptsoft.com)"
  35  *    The word 'cryptographic' can be left out if the rouines from the library
  36  *    being used are not cryptographic related :-).
  37  * 4. If you include any Windows specific code (or a derivative thereof) from
  38  *    the apps directory (application code) you must include an acknowledgement:
  39  *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
  40  *
  41  * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
  42  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  43  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  44  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  45  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  46  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  47  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  48  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  49  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  50  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  51  * SUCH DAMAGE.
  52  *
  53  * The licence and distribution terms for any publically available version or
  54  * derivative of this code cannot be changed.  i.e. this code cannot simply be
  55  * copied and put under another distribution licence
  56  * [including the GNU Public Licence.]
  57  */
  58
  59 #include <stdio.h>
  60
  61 #include <openssl/bn.h>
  62 #include <openssl/dh.h>
  63
  64 /*
  65  * Check that p is a safe prime and
  66  * if g is 2, 3 or 5, check that it is a suitable generator
  67  * where
  68  * for 2, p mod 24 == 11
  69  * for 3, p mod 12 == 5
  70  * for 5, p mod 10 == 3 or 7
  71  * should hold.
  72  */
  73
  74 int
  75 DH_check(const DH *dh, int *ret)
  76 {
  77         int ok = 0;
  78         BN_CTX *ctx = NULL;
  79         BN_ULONG l;
  80         BIGNUM *q = NULL;
  81
  82         *ret = 0;
  83         ctx = BN_CTX_new();
  84         if (ctx == NULL)
  85                 goto err;
  86         q = BN_new();
  87         if (q == NULL)
  88                 goto err;
  89
  90         if (BN_is_word(dh->g, DH_GENERATOR_2)) {
  91                 l = BN_mod_word(dh->p, 24);
  92                 if (l == (BN_ULONG)-1)
  93                         goto err;
  94                 if (l != 11)
  95                         *ret |= DH_NOT_SUITABLE_GENERATOR;
  96         } else if (BN_is_word(dh->g, DH_GENERATOR_5)) {
  97                 l = BN_mod_word(dh->p, 10);
  98                 if (l == (BN_ULONG)-1)
  99                         goto err;
 100                 if (l != 3 && l != 7)
 101                         *ret |= DH_NOT_SUITABLE_GENERATOR;
 102         } else
 103                 *ret |= DH_UNABLE_TO_CHECK_GENERATOR;
 104
 105         if (!BN_is_prime_ex(dh->p, BN_prime_checks, ctx, NULL))
 106                 *ret |= DH_CHECK_P_NOT_PRIME;
 107         else {
 108                 if (!BN_rshift1(q, dh->p))
 109                         goto err;
 110                 if (!BN_is_prime_ex(q, BN_prime_checks, ctx, NULL))
 111                         *ret |= DH_CHECK_P_NOT_SAFE_PRIME;
 112         }
 113         ok = 1;
 114 err:
 115         BN_CTX_free(ctx);
 116         BN_free(q);
 117         return ok;
 118 }
 119
 120 int
 121 DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
 122 {
 123         BIGNUM *q = NULL;
 124
 125         *ret = 0;
 126         q = BN_new();
 127         if (q == NULL)
 128                 return 0;
 129         BN_set_word(q, 1);
 130         if (BN_cmp(pub_key, q) <= 0)
 131                 *ret |= DH_CHECK_PUBKEY_TOO_SMALL;
 132         BN_copy(q, dh->p);
 133         BN_sub_word(q, 1);
 134         if (BN_cmp(pub_key, q) >= 0)
 135                 *ret |= DH_CHECK_PUBKEY_TOO_LARGE;
 136
 137         BN_free(q);
 138         return 1;
 139 }