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