1/* crypto/dh/dh_check.c */
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#include "cryptlib.h"
61#include <openssl/bn.h>
62#include <openssl/dh.h>
63
64/* Check that p is a safe prime and
65 * if g is 2, 3 or 5, check that it is a suitable generator
66 * where
67 * for 2, p mod 24 == 11
68 * for 3, p mod 12 == 5
69 * for 5, p mod 10 == 3 or 7
70 * should hold.
71 */
72
73int DH_check(const DH *dh, int *ret)
74	{
75	int ok=0;
76	BN_CTX *ctx=NULL;
77	BN_ULONG l;
78	BIGNUM *q=NULL;
79
80	*ret=0;
81	ctx=BN_CTX_new();
82	if (ctx == NULL) goto err;
83	q=BN_new();
84	if (q == NULL) goto err;
85
86	if (BN_is_word(dh->g,DH_GENERATOR_2))
87		{
88		l=BN_mod_word(dh->p,24);
89		if (l != 11) *ret|=DH_NOT_SUITABLE_GENERATOR;
90		}
91#if 0
92	else if (BN_is_word(dh->g,DH_GENERATOR_3))
93		{
94		l=BN_mod_word(dh->p,12);
95		if (l != 5) *ret|=DH_NOT_SUITABLE_GENERATOR;
96		}
97#endif
98	else if (BN_is_word(dh->g,DH_GENERATOR_5))
99		{
100		l=BN_mod_word(dh->p,10);
101		if ((l != 3) && (l != 7))
102			*ret|=DH_NOT_SUITABLE_GENERATOR;
103		}
104	else
105		*ret|=DH_UNABLE_TO_CHECK_GENERATOR;
106
107	if (!BN_is_prime_ex(dh->p,BN_prime_checks,ctx,NULL))
108		*ret|=DH_CHECK_P_NOT_PRIME;
109	else
110		{
111		if (!BN_rshift1(q,dh->p)) goto err;
112		if (!BN_is_prime_ex(q,BN_prime_checks,ctx,NULL))
113			*ret|=DH_CHECK_P_NOT_SAFE_PRIME;
114		}
115	ok=1;
116err:
117	if (ctx != NULL) BN_CTX_free(ctx);
118	if (q != NULL) BN_free(q);
119	return(ok);
120	}
121
122int DH_check_pub_key(const DH *dh, const BIGNUM *pub_key, int *ret)
123	{
124	int ok=0;
125	BIGNUM *q=NULL;
126
127	*ret=0;
128	q=BN_new();
129	if (q == NULL) goto err;
130	BN_set_word(q,1);
131	if (BN_cmp(pub_key,q)<=0)
132		*ret|=DH_CHECK_PUBKEY_TOO_SMALL;
133	BN_copy(q,dh->p);
134	BN_sub_word(q,1);
135	if (BN_cmp(pub_key,q)>=0)
136		*ret|=DH_CHECK_PUBKEY_TOO_LARGE;
137
138	ok = 1;
139err:
140	if (q != NULL) BN_free(q);
141	return(ok);
142	}
143