dh_gen.c revision 296465 
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/*
60 * NB: These functions have been upgraded - the previous prototypes are in
61 * dh_depr.c as wrappers to these ones.  - Geoff
62 */
63
64#include <stdio.h>
65#include "cryptlib.h"
66#include <openssl/bn.h>
67#include <openssl/dh.h>
68
69#ifndef OPENSSL_FIPS
70
71static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
72                                BN_GENCB *cb);
73
74int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
75                              BN_GENCB *cb)
76{
77    if (ret->meth->generate_params)
78        return ret->meth->generate_params(ret, prime_len, generator, cb);
79    return dh_builtin_genparams(ret, prime_len, generator, cb);
80}
81
82/*-
83 * We generate DH parameters as follows
84 * find a prime q which is prime_len/2 bits long.
85 * p=(2*q)+1 or (p-1)/2 = q
86 * For this case, g is a generator if
87 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
88 * Since the factors of p-1 are q and 2, we just need to check
89 * g^2 mod p != 1 and g^q mod p != 1.
90 *
91 * Having said all that,
92 * there is another special case method for the generators 2, 3 and 5.
93 * for 2, p mod 24 == 11
94 * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
95 * for 5, p mod 10 == 3 or 7
96 *
97 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
98 * special generators and for answering some of my questions.
99 *
100 * I've implemented the second simple method :-).
101 * Since DH should be using a safe prime (both p and q are prime),
102 * this generator function can take a very very long time to run.
103 */
104/*
105 * Actually there is no reason to insist that 'generator' be a generator.
106 * It's just as OK (and in some sense better) to use a generator of the
107 * order-q subgroup.
108 */
109static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
110                                BN_GENCB *cb)
111{
112    BIGNUM *t1, *t2;
113    int g, ok = -1;
114    BN_CTX *ctx = NULL;
115
116    ctx = BN_CTX_new();
117    if (ctx == NULL)
118        goto err;
119    BN_CTX_start(ctx);
120    t1 = BN_CTX_get(ctx);
121    t2 = BN_CTX_get(ctx);
122    if (t1 == NULL || t2 == NULL)
123        goto err;
124
125    /* Make sure 'ret' has the necessary elements */
126    if (!ret->p && ((ret->p = BN_new()) == NULL))
127        goto err;
128    if (!ret->g && ((ret->g = BN_new()) == NULL))
129        goto err;
130
131    if (generator <= 1) {
132        DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
133        goto err;
134    }
135    if (generator == DH_GENERATOR_2) {
136        if (!BN_set_word(t1, 24))
137            goto err;
138        if (!BN_set_word(t2, 11))
139            goto err;
140        g = 2;
141    }
142# if 0                          /* does not work for safe primes */
143    else if (generator == DH_GENERATOR_3) {
144        if (!BN_set_word(t1, 12))
145            goto err;
146        if (!BN_set_word(t2, 5))
147            goto err;
148        g = 3;
149    }
150# endif
151    else if (generator == DH_GENERATOR_5) {
152        if (!BN_set_word(t1, 10))
153            goto err;
154        if (!BN_set_word(t2, 3))
155            goto err;
156        /*
157         * BN_set_word(t3,7); just have to miss out on these ones :-(
158         */
159        g = 5;
160    } else {
161        /*
162         * in the general case, don't worry if 'generator' is a generator or
163         * not: since we are using safe primes, it will generate either an
164         * order-q or an order-2q group, which both is OK
165         */
166        if (!BN_set_word(t1, 2))
167            goto err;
168        if (!BN_set_word(t2, 1))
169            goto err;
170        g = generator;
171    }
172
173    if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
174        goto err;
175    if (!BN_GENCB_call(cb, 3, 0))
176        goto err;
177    if (!BN_set_word(ret->g, g))
178        goto err;
179    ok = 1;
180 err:
181    if (ok == -1) {
182        DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
183        ok = 0;
184    }
185
186    if (ctx != NULL) {
187        BN_CTX_end(ctx);
188        BN_CTX_free(ctx);
189    }
190    return ok;
191}
192
193#endif
194