dh_key.c revision 312826 
1/* crypto/dh/dh_key.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/rand.h>
63#include <openssl/dh.h>
64
65static int generate_key(DH *dh);
66static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
67static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
68                         const BIGNUM *a, const BIGNUM *p,
69                         const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
70static int dh_init(DH *dh);
71static int dh_finish(DH *dh);
72
73int DH_generate_key(DH *dh)
74{
75#ifdef OPENSSL_FIPS
76    if (FIPS_mode() && !(dh->meth->flags & DH_FLAG_FIPS_METHOD)
77        && !(dh->flags & DH_FLAG_NON_FIPS_ALLOW)) {
78        DHerr(DH_F_DH_GENERATE_KEY, DH_R_NON_FIPS_METHOD);
79        return 0;
80    }
81#endif
82    return dh->meth->generate_key(dh);
83}
84
85int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
86{
87#ifdef OPENSSL_FIPS
88    if (FIPS_mode() && !(dh->meth->flags & DH_FLAG_FIPS_METHOD)
89        && !(dh->flags & DH_FLAG_NON_FIPS_ALLOW)) {
90        DHerr(DH_F_DH_COMPUTE_KEY, DH_R_NON_FIPS_METHOD);
91        return 0;
92    }
93#endif
94    return dh->meth->compute_key(key, pub_key, dh);
95}
96
97int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
98{
99    int rv, pad;
100    rv = dh->meth->compute_key(key, pub_key, dh);
101    if (rv <= 0)
102        return rv;
103    pad = BN_num_bytes(dh->p) - rv;
104    if (pad > 0) {
105        memmove(key + pad, key, rv);
106        memset(key, 0, pad);
107    }
108    return rv + pad;
109}
110
111static DH_METHOD dh_ossl = {
112    "OpenSSL DH Method",
113    generate_key,
114    compute_key,
115    dh_bn_mod_exp,
116    dh_init,
117    dh_finish,
118    0,
119    NULL,
120    NULL
121};
122
123const DH_METHOD *DH_OpenSSL(void)
124{
125    return &dh_ossl;
126}
127
128static int generate_key(DH *dh)
129{
130    int ok = 0;
131    int generate_new_key = 0;
132    unsigned l;
133    BN_CTX *ctx;
134    BN_MONT_CTX *mont = NULL;
135    BIGNUM *pub_key = NULL, *priv_key = NULL;
136
137    ctx = BN_CTX_new();
138    if (ctx == NULL)
139        goto err;
140
141    if (dh->priv_key == NULL) {
142        priv_key = BN_new();
143        if (priv_key == NULL)
144            goto err;
145        generate_new_key = 1;
146    } else
147        priv_key = dh->priv_key;
148
149    if (dh->pub_key == NULL) {
150        pub_key = BN_new();
151        if (pub_key == NULL)
152            goto err;
153    } else
154        pub_key = dh->pub_key;
155
156    if (dh->flags & DH_FLAG_CACHE_MONT_P) {
157        mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
158                                      CRYPTO_LOCK_DH, dh->p, ctx);
159        if (!mont)
160            goto err;
161    }
162
163    if (generate_new_key) {
164        if (dh->q) {
165            do {
166                if (!BN_rand_range(priv_key, dh->q))
167                    goto err;
168            }
169            while (BN_is_zero(priv_key) || BN_is_one(priv_key));
170        } else {
171            /* secret exponent length */
172            l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
173            if (!BN_rand(priv_key, l, 0, 0))
174                goto err;
175        }
176    }
177
178    {
179        BIGNUM local_prk;
180        BIGNUM *prk;
181
182        if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {
183            BN_init(&local_prk);
184            prk = &local_prk;
185            BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
186        } else
187            prk = priv_key;
188
189        if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont))
190            goto err;
191    }
192
193    dh->pub_key = pub_key;
194    dh->priv_key = priv_key;
195    ok = 1;
196 err:
197    if (ok != 1)
198        DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
199
200    if ((pub_key != NULL) && (dh->pub_key == NULL))
201        BN_free(pub_key);
202    if ((priv_key != NULL) && (dh->priv_key == NULL))
203        BN_free(priv_key);
204    BN_CTX_free(ctx);
205    return (ok);
206}
207
208static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
209{
210    BN_CTX *ctx = NULL;
211    BN_MONT_CTX *mont = NULL;
212    BIGNUM *tmp;
213    int ret = -1;
214    int check_result;
215
216    if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
217        DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
218        goto err;
219    }
220
221    ctx = BN_CTX_new();
222    if (ctx == NULL)
223        goto err;
224    BN_CTX_start(ctx);
225    tmp = BN_CTX_get(ctx);
226    if (tmp == NULL)
227        goto err;
228
229    if (dh->priv_key == NULL) {
230        DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
231        goto err;
232    }
233
234    if (dh->flags & DH_FLAG_CACHE_MONT_P) {
235        mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
236                                      CRYPTO_LOCK_DH, dh->p, ctx);
237        if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {
238            /* XXX */
239            BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
240        }
241        if (!mont)
242            goto err;
243    }
244
245    if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
246        DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
247        goto err;
248    }
249
250    if (!dh->
251        meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
252        DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
253        goto err;
254    }
255
256    ret = BN_bn2bin(tmp, key);
257 err:
258    if (ctx != NULL) {
259        BN_CTX_end(ctx);
260        BN_CTX_free(ctx);
261    }
262    return (ret);
263}
264
265static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
266                         const BIGNUM *a, const BIGNUM *p,
267                         const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
268{
269    /*
270     * If a is only one word long and constant time is false, use the faster
271     * exponenentiation function.
272     */
273    if (a->top == 1 && ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) != 0)) {
274        BN_ULONG A = a->d[0];
275        return BN_mod_exp_mont_word(r, A, p, m, ctx, m_ctx);
276    } else
277        return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
278}
279
280static int dh_init(DH *dh)
281{
282    dh->flags |= DH_FLAG_CACHE_MONT_P;
283    return (1);
284}
285
286static int dh_finish(DH *dh)
287{
288    if (dh->method_mont_p)
289        BN_MONT_CTX_free(dh->method_mont_p);
290    return (1);
291}
292