1 /* crypto/dh/dh_gen.c */
2 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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.
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).
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.
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
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)"
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
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.]
60 * NB: These functions have been upgraded - the previous prototypes are in
61 * dh_depr.c as wrappers to these ones. - Geoff
66 #include <openssl/bn.h>
67 #include <openssl/dh.h>
70 # include <openssl/fips.h>
73 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
76 int DH_generate_parameters_ex(DH *ret, int prime_len, int generator,
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);
86 if (ret->meth->generate_params)
87 return ret->meth->generate_params(ret, prime_len, generator, cb);
90 return FIPS_dh_generate_parameters_ex(ret, prime_len, generator, cb);
92 return dh_builtin_genparams(ret, prime_len, generator, cb);
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.
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
110 * Thanks to Phil Karn <karn@qualcomm.com> for the pointers about the
111 * special generators and for answering some of my questions.
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.
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
122 static int dh_builtin_genparams(DH *ret, int prime_len, int generator,
133 t1 = BN_CTX_get(ctx);
134 t2 = BN_CTX_get(ctx);
135 if (t1 == NULL || t2 == NULL)
138 /* Make sure 'ret' has the necessary elements */
139 if (!ret->p && ((ret->p = BN_new()) == NULL))
141 if (!ret->g && ((ret->g = BN_new()) == NULL))
144 if (generator <= 1) {
145 DHerr(DH_F_DH_BUILTIN_GENPARAMS, DH_R_BAD_GENERATOR);
148 if (generator == DH_GENERATOR_2) {
149 if (!BN_set_word(t1, 24))
151 if (!BN_set_word(t2, 11))
155 #if 0 /* does not work for safe primes */
156 else if (generator == DH_GENERATOR_3) {
157 if (!BN_set_word(t1, 12))
159 if (!BN_set_word(t2, 5))
164 else if (generator == DH_GENERATOR_5) {
165 if (!BN_set_word(t1, 10))
167 if (!BN_set_word(t2, 3))
170 * BN_set_word(t3,7); just have to miss out on these ones :-(
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
179 if (!BN_set_word(t1, 2))
181 if (!BN_set_word(t2, 1))
186 if (!BN_generate_prime_ex(ret->p, prime_len, 1, t1, t2, cb))
188 if (!BN_GENCB_call(cb, 3, 0))
190 if (!BN_set_word(ret->g, g))
195 DHerr(DH_F_DH_BUILTIN_GENPARAMS, ERR_R_BN_LIB);