dh_gen.c revision 296341 
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#ifdef OPENSSL_FIPS
70# include <openssl/fips.h>
71#endif
72
73static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
74                                BN_GENCB *cb);
75
76int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
77                              BN_GENCB *cb)
78{
79#ifdef OPENSSL_FIPS
80    if (FIPS_mode() && !(ret->meth->flags & DH_FLAG_FIPS_METHOD)
81        && !(ret->flags & DH_FLAG_NON_FIPS_ALLOW)) {
82        DHerr(DH_F_DH_GENERATE_PARAMETERS_EX, DH_R_NON_FIPS_METHOD);
83        return 0;
84    }
85#endif
86    if (ret->meth->generate_params)
87        return ret->meth->generate_params(ret, prime_len, generator, cb);
88#ifdef OPENSSL_FIPS
89    if (FIPS_mode())
90        return FIPS_dh_generate_parameters_ex(ret, prime_len, generator, cb);
91#endif
92    return dh_builtin_genparams(ret, prime_len, generator, cb);
93}
94
95/*-
96 * We generate DH parameters as follows
97 * find a prime q which is prime_len/2 bits long.
98 * p=(2*q)+1 or (p-1)/2 = q
99 * For this case, g is a generator if
100 * g^((p-1)/q) mod p != 1 for values of q which are the factors of p-1.
101 * Since the factors of p-1 are q and 2, we just need to check
102 * g^2 mod p != 1 and g^q mod p != 1.
103 *
104 * Having said all that,
105 * there is another special case method for the generators 2, 3 and 5.
106 * for 2, p mod 24 == 11
107 * for 3, p mod 12 == 5  <<<<< does not work for safe primes.
108 * for 5, p mod 10 == 3 or 7
109 *
110 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
111 * special generators and for answering some of my questions.
112 *
113 * I've implemented the second simple method :-).
114 * Since DH should be using a safe prime (both p and q are prime),
115 * this generator function can take a very very long time to run.
116 */
117/*
118 * Actually there is no reason to insist that 'generator' be a generator.
119 * It's just as OK (and in some sense better) to use a generator of the
120 * order-q subgroup.
121 */
122static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
123                                BN_GENCB *cb)
124{
125    BIGNUM *t1, *t2;
126    int g, ok = -1;
127    BN_CTX *ctx = NULL;
128
129    ctx = BN_CTX_new();
130    if (ctx == NULL)
131        goto err;
132    BN_CTX_start(ctx);
133    t1 = BN_CTX_get(ctx);
134    t2 = BN_CTX_get(ctx);
135    if (t1 == NULL || t2 == NULL)
136        goto err;
137
138    /* Make sure 'ret' has the necessary elements */
139    if (!ret->p && ((ret->p = BN_new()) == NULL))
140        goto err;
141    if (!ret->g && ((ret->g = BN_new()) == NULL))
142        goto err;
143
144    if (generator <= 1) {
145        DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
146        goto err;
147    }
148    if (generator == DH_GENERATOR_2) {
149        if (!BN_set_word(t1, 24))
150            goto err;
151        if (!BN_set_word(t2, 11))
152            goto err;
153        g = 2;
154    }
155#if 0                           /* does not work for safe primes */
156    else if (generator == DH_GENERATOR_3) {
157        if (!BN_set_word(t1, 12))
158            goto err;
159        if (!BN_set_word(t2, 5))
160            goto err;
161        g = 3;
162    }
163#endif
164    else if (generator == DH_GENERATOR_5) {
165        if (!BN_set_word(t1, 10))
166            goto err;
167        if (!BN_set_word(t2, 3))
168            goto err;
169        /*
170         * BN_set_word(t3,7); just have to miss out on these ones :-(
171         */
172        g = 5;
173    } else {
174        /*
175         * in the general case, don't worry if 'generator' is a generator or
176         * not: since we are using safe primes, it will generate either an
177         * order-q or an order-2q group, which both is OK
178         */
179        if (!BN_set_word(t1, 2))
180            goto err;
181        if (!BN_set_word(t2, 1))
182            goto err;
183        g = generator;
184    }
185
186    if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
187        goto err;
188    if (!BN_GENCB_call(cb, 3, 0))
189        goto err;
190    if (!BN_set_word(ret->g, g))
191        goto err;
192    ok = 1;
193 err:
194    if (ok == -1) {
195        DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);
196        ok = 0;
197    }
198
199    if (ctx != NULL) {
200        BN_CTX_end(ctx);
201        BN_CTX_free(ctx);
202    }
203    return ok;
204}
205