dsa_ossl.c revision 325337 
1/* crypto/dsa/dsa_ossl.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/* Original version from Steven Schoch <schoch@sheba.arc.nasa.gov> */
60
61#include <stdio.h>
62#include "cryptlib.h"
63#include <openssl/bn.h>
64#include <openssl/sha.h>
65#include <openssl/dsa.h>
66#include <openssl/rand.h>
67#include <openssl/asn1.h>
68
69static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
70static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
71                          BIGNUM **rp);
72static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
73                         DSA_SIG *sig, DSA *dsa);
74static int dsa_init(DSA *dsa);
75static int dsa_finish(DSA *dsa);
76
77static DSA_METHOD openssl_dsa_meth = {
78    "OpenSSL DSA method",
79    dsa_do_sign,
80    dsa_sign_setup,
81    dsa_do_verify,
82    NULL,                       /* dsa_mod_exp, */
83    NULL,                       /* dsa_bn_mod_exp, */
84    dsa_init,
85    dsa_finish,
86    0,
87    NULL,
88    NULL,
89    NULL
90};
91
92/*-
93 * These macro wrappers replace attempts to use the dsa_mod_exp() and
94 * bn_mod_exp() handlers in the DSA_METHOD structure. We avoid the problem of
95 * having a the macro work as an expression by bundling an "err_instr". So;
96 *
97 *     if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx,
98 *                 dsa->method_mont_p)) goto err;
99 *
100 * can be replaced by;
101 *
102 *     DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, &k, dsa->p, ctx,
103 *                 dsa->method_mont_p);
104 */
105
106#define DSA_MOD_EXP(err_instr,dsa,rr,a1,p1,a2,p2,m,ctx,in_mont) \
107        do { \
108        int _tmp_res53; \
109        if ((dsa)->meth->dsa_mod_exp) \
110                _tmp_res53 = (dsa)->meth->dsa_mod_exp((dsa), (rr), (a1), (p1), \
111                                (a2), (p2), (m), (ctx), (in_mont)); \
112        else \
113                _tmp_res53 = BN_mod_exp2_mont((rr), (a1), (p1), (a2), (p2), \
114                                (m), (ctx), (in_mont)); \
115        if (!_tmp_res53) err_instr; \
116        } while(0)
117#define DSA_BN_MOD_EXP(err_instr,dsa,r,a,p,m,ctx,m_ctx) \
118        do { \
119        int _tmp_res53; \
120        if ((dsa)->meth->bn_mod_exp) \
121                _tmp_res53 = (dsa)->meth->bn_mod_exp((dsa), (r), (a), (p), \
122                                (m), (ctx), (m_ctx)); \
123        else \
124                _tmp_res53 = BN_mod_exp_mont((r), (a), (p), (m), (ctx), (m_ctx)); \
125        if (!_tmp_res53) err_instr; \
126        } while(0)
127
128const DSA_METHOD *DSA_OpenSSL(void)
129{
130    return &openssl_dsa_meth;
131}
132
133static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
134{
135    BIGNUM *kinv = NULL, *r = NULL, *s = NULL;
136    BIGNUM m;
137    BIGNUM xr;
138    BN_CTX *ctx = NULL;
139    int reason = ERR_R_BN_LIB;
140    DSA_SIG *ret = NULL;
141    int noredo = 0;
142
143    BN_init(&m);
144    BN_init(&xr);
145
146    if (!dsa->p || !dsa->q || !dsa->g) {
147        reason = DSA_R_MISSING_PARAMETERS;
148        goto err;
149    }
150
151    s = BN_new();
152    if (s == NULL)
153        goto err;
154    ctx = BN_CTX_new();
155    if (ctx == NULL)
156        goto err;
157 redo:
158    if ((dsa->kinv == NULL) || (dsa->r == NULL)) {
159        if (!DSA_sign_setup(dsa, ctx, &kinv, &r))
160            goto err;
161    } else {
162        kinv = dsa->kinv;
163        dsa->kinv = NULL;
164        r = dsa->r;
165        dsa->r = NULL;
166        noredo = 1;
167    }
168
169    if (dlen > BN_num_bytes(dsa->q))
170        /*
171         * if the digest length is greater than the size of q use the
172         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
173         * 4.2
174         */
175        dlen = BN_num_bytes(dsa->q);
176    if (BN_bin2bn(dgst, dlen, &m) == NULL)
177        goto err;
178
179    /* Compute  s = inv(k) (m + xr) mod q */
180    if (!BN_mod_mul(&xr, dsa->priv_key, r, dsa->q, ctx))
181        goto err;               /* s = xr */
182    if (!BN_add(s, &xr, &m))
183        goto err;               /* s = m + xr */
184    if (BN_cmp(s, dsa->q) > 0)
185        if (!BN_sub(s, s, dsa->q))
186            goto err;
187    if (!BN_mod_mul(s, s, kinv, dsa->q, ctx))
188        goto err;
189
190    /*
191     * Redo if r or s is zero as required by FIPS 186-3: this is very
192     * unlikely.
193     */
194    if (BN_is_zero(r) || BN_is_zero(s)) {
195        if (noredo) {
196            reason = DSA_R_NEED_NEW_SETUP_VALUES;
197            goto err;
198        }
199        goto redo;
200    }
201    ret = DSA_SIG_new();
202    if (ret == NULL)
203        goto err;
204    ret->r = r;
205    ret->s = s;
206
207 err:
208    if (ret == NULL) {
209        DSAerr(DSA_F_DSA_DO_SIGN, reason);
210        BN_free(r);
211        BN_free(s);
212    }
213    if (ctx != NULL)
214        BN_CTX_free(ctx);
215    BN_clear_free(&m);
216    BN_clear_free(&xr);
217    if (kinv != NULL)           /* dsa->kinv is NULL now if we used it */
218        BN_clear_free(kinv);
219    return (ret);
220}
221
222static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
223                          BIGNUM **rp)
224{
225    BN_CTX *ctx;
226    BIGNUM k, kq, *K, *kinv = NULL, *r = NULL;
227    BIGNUM l, m;
228    int ret = 0;
229    int q_bits;
230
231    if (!dsa->p || !dsa->q || !dsa->g) {
232        DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
233        return 0;
234    }
235
236    BN_init(&k);
237    BN_init(&kq);
238    BN_init(&l);
239    BN_init(&m);
240
241    if (ctx_in == NULL) {
242        if ((ctx = BN_CTX_new()) == NULL)
243            goto err;
244    } else
245        ctx = ctx_in;
246
247    if ((r = BN_new()) == NULL)
248        goto err;
249
250    /* Preallocate space */
251    q_bits = BN_num_bits(dsa->q);
252    if (!BN_set_bit(&k, q_bits)
253        || !BN_set_bit(&l, q_bits)
254        || !BN_set_bit(&m, q_bits))
255        goto err;
256
257    /* Get random k */
258    do
259        if (!BN_rand_range(&k, dsa->q))
260            goto err;
261    while (BN_is_zero(&k));
262
263    if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
264        BN_set_flags(&k, BN_FLG_CONSTTIME);
265    }
266
267
268    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
269        if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
270                                    CRYPTO_LOCK_DSA, dsa->p, ctx))
271            goto err;
272    }
273
274    /* Compute r = (g^k mod p) mod q */
275
276    if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
277        /*
278         * We do not want timing information to leak the length of k, so we
279         * compute G^k using an equivalent scalar of fixed bit-length.
280         *
281         * We unconditionally perform both of these additions to prevent a
282         * small timing information leakage.  We then choose the sum that is
283         * one bit longer than the modulus.
284         *
285         * TODO: revisit the BN_copy aiming for a memory access agnostic
286         * conditional copy.
287         */
288        if (!BN_add(&l, &k, dsa->q)
289            || !BN_add(&m, &l, dsa->q)
290            || !BN_copy(&kq, BN_num_bits(&l) > q_bits ? &l : &m))
291            goto err;
292
293        BN_set_flags(&kq, BN_FLG_CONSTTIME);
294
295        K = &kq;
296    } else {
297        K = &k;
298    }
299
300    DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx,
301                   dsa->method_mont_p);
302    if (!BN_mod(r, r, dsa->q, ctx))
303        goto err;
304
305    /* Compute  part of 's = inv(k) (m + xr) mod q' */
306    if ((kinv = BN_mod_inverse(NULL, &k, dsa->q, ctx)) == NULL)
307        goto err;
308
309    if (*kinvp != NULL)
310        BN_clear_free(*kinvp);
311    *kinvp = kinv;
312    kinv = NULL;
313    if (*rp != NULL)
314        BN_clear_free(*rp);
315    *rp = r;
316    ret = 1;
317 err:
318    if (!ret) {
319        DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
320        if (r != NULL)
321            BN_clear_free(r);
322    }
323    if (ctx_in == NULL)
324        BN_CTX_free(ctx);
325    BN_clear_free(&k);
326    BN_clear_free(&kq);
327    BN_clear_free(&l);
328    BN_clear_free(&m);
329    return ret;
330}
331
332static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
333                         DSA_SIG *sig, DSA *dsa)
334{
335    BN_CTX *ctx;
336    BIGNUM u1, u2, t1;
337    BN_MONT_CTX *mont = NULL;
338    int ret = -1, i;
339    if (!dsa->p || !dsa->q || !dsa->g) {
340        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
341        return -1;
342    }
343
344    i = BN_num_bits(dsa->q);
345    /* fips 186-3 allows only different sizes for q */
346    if (i != 160 && i != 224 && i != 256) {
347        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
348        return -1;
349    }
350
351    if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
352        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
353        return -1;
354    }
355    BN_init(&u1);
356    BN_init(&u2);
357    BN_init(&t1);
358
359    if ((ctx = BN_CTX_new()) == NULL)
360        goto err;
361
362    if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||
363        BN_ucmp(sig->r, dsa->q) >= 0) {
364        ret = 0;
365        goto err;
366    }
367    if (BN_is_zero(sig->s) || BN_is_negative(sig->s) ||
368        BN_ucmp(sig->s, dsa->q) >= 0) {
369        ret = 0;
370        goto err;
371    }
372
373    /*
374     * Calculate W = inv(S) mod Q save W in u2
375     */
376    if ((BN_mod_inverse(&u2, sig->s, dsa->q, ctx)) == NULL)
377        goto err;
378
379    /* save M in u1 */
380    if (dgst_len > (i >> 3))
381        /*
382         * if the digest length is greater than the size of q use the
383         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
384         * 4.2
385         */
386        dgst_len = (i >> 3);
387    if (BN_bin2bn(dgst, dgst_len, &u1) == NULL)
388        goto err;
389
390    /* u1 = M * w mod q */
391    if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx))
392        goto err;
393
394    /* u2 = r * w mod q */
395    if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx))
396        goto err;
397
398    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
399        mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
400                                      CRYPTO_LOCK_DSA, dsa->p, ctx);
401        if (!mont)
402            goto err;
403    }
404
405    DSA_MOD_EXP(goto err, dsa, &t1, dsa->g, &u1, dsa->pub_key, &u2, dsa->p,
406                ctx, mont);
407    /* BN_copy(&u1,&t1); */
408    /* let u1 = u1 mod q */
409    if (!BN_mod(&u1, &t1, dsa->q, ctx))
410        goto err;
411
412    /*
413     * V is now in u1.  If the signature is correct, it will be equal to R.
414     */
415    ret = (BN_ucmp(&u1, sig->r) == 0);
416
417 err:
418    if (ret < 0)
419        DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
420    if (ctx != NULL)
421        BN_CTX_free(ctx);
422    BN_free(&u1);
423    BN_free(&u2);
424    BN_free(&t1);
425    return (ret);
426}
427
428static int dsa_init(DSA *dsa)
429{
430    dsa->flags |= DSA_FLAG_CACHE_MONT_P;
431    return (1);
432}
433
434static int dsa_finish(DSA *dsa)
435{
436    if (dsa->method_mont_p)
437        BN_MONT_CTX_free(dsa->method_mont_p);
438    return (1);
439}
440