1/* crypto/dh/dh_gen.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 <string.h>
61#include <openssl/err.h>
62#include <openssl/bn.h>
63#ifndef OPENSSL_NO_DH
64#include <openssl/dh.h>
65#endif
66#include <openssl/fips.h>
67
68#ifndef OPENSSL_NO_DH
69#ifdef OPENSSL_FIPS
70
71/* We generate DH parameters as follows
72 * find a prime q which is prime_len/2 bits long.
73 * p=(2*q)+1 or (p-1)/2 = q
74 * For this case, g is a generator if
75 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
76 * Since the factors of p-1 are q and 2, we just need to check
77 * g^2 mod p != 1 and g^q mod p != 1.
78 *
79 * Having said all that,
80 * there is another special case method for the generators 2, 3 and 5.
81 * for 2, p mod 24 == 11
82 * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
83 * for 5, p mod 10 == 3 or 7
84 *
85 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
86 * special generators and for answering some of my questions.
87 *
88 * I've implemented the second simple method :-).
89 * Since DH should be using a safe prime (both p and q are prime),
90 * this generator function can take a very very long time to run.
91 */
92/* Actually there is no reason to insist that 'generator' be a generator.
93 * It's just as OK (and in some sense better) to use a generator of the
94 * order-q subgroup.
95 */
96
97DH *DH_generate_parameters(int prime_len, int generator,
98	     void (*callback)(int,int,void *), void *cb_arg)
99	{
100	BIGNUM *p=NULL,*t1,*t2;
101	DH *ret=NULL;
102	int g,ok= -1;
103	BN_CTX *ctx=NULL;
104
105	if(FIPS_selftest_failed())
106		{
107		FIPSerr(FIPS_F_DH_GENERATE_PARAMETERS,FIPS_R_FIPS_SELFTEST_FAILED);
108		return NULL;
109		}
110
111	ret=DH_new();
112	if (ret == NULL) goto err;
113	ctx=BN_CTX_new();
114	if (ctx == NULL) goto err;
115	BN_CTX_start(ctx);
116	t1 = BN_CTX_get(ctx);
117	t2 = BN_CTX_get(ctx);
118	if (t1 == NULL || t2 == NULL) goto err;
119
120	if (generator <= 1)
121		{
122		DHerr(DH_F_DH_GENERATE_PARAMETERS, DH_R_BAD_GENERATOR);
123		goto err;
124		}
125	if (generator == DH_GENERATOR_2)
126		{
127		if (!BN_set_word(t1,24)) goto err;
128		if (!BN_set_word(t2,11)) goto err;
129		g=2;
130		}
131#if 0 /* does not work for safe primes */
132	else if (generator == DH_GENERATOR_3)
133		{
134		if (!BN_set_word(t1,12)) goto err;
135		if (!BN_set_word(t2,5)) goto err;
136		g=3;
137		}
138#endif
139	else if (generator == DH_GENERATOR_5)
140		{
141		if (!BN_set_word(t1,10)) goto err;
142		if (!BN_set_word(t2,3)) goto err;
143		/* BN_set_word(t3,7); just have to miss
144		 * out on these ones :-( */
145		g=5;
146		}
147	else
148		{
149		/* in the general case, don't worry if 'generator' is a
150		 * generator or not: since we are using safe primes,
151		 * it will generate either an order-q or an order-2q group,
152		 * which both is OK */
153		if (!BN_set_word(t1,2)) goto err;
154		if (!BN_set_word(t2,1)) goto err;
155		g=generator;
156		}
157
158	p=BN_generate_prime(NULL,prime_len,1,t1,t2,callback,cb_arg);
159	if (p == NULL) goto err;
160	if (callback != NULL) callback(3,0,cb_arg);
161	ret->p=p;
162	ret->g=BN_new();
163	if (!BN_set_word(ret->g,g)) goto err;
164	ok=1;
165err:
166	if (ok == -1)
167		{
168		DHerr(DH_F_DH_GENERATE_PARAMETERS,ERR_R_BN_LIB);
169		ok=0;
170		}
171
172	if (ctx != NULL)
173		{
174		BN_CTX_end(ctx);
175		BN_CTX_free(ctx);
176		}
177	if (!ok && (ret != NULL))
178		{
179		DH_free(ret);
180		ret=NULL;
181		}
182	return(ret);
183	}
184
185#endif
186#endif
187