/src/openssl/crypto/dsa/dsa_ossl.c

Source (jump to first uncovered line)
/*
 * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include <openssl/sha.h>
#include "dsa_locl.h"
#include <openssl/asn1.h>

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
                                    BIGNUM **rp);
static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
                          BIGNUM **rp, const unsigned char *dgst, int dlen);
static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
                         DSA_SIG *sig, DSA *dsa);
static int dsa_init(DSA *dsa);
static int dsa_finish(DSA *dsa);

static DSA_METHOD openssl_dsa_meth = {
    "OpenSSL DSA method",
    dsa_do_sign,
    dsa_sign_setup_no_digest,
    dsa_do_verify,
    NULL,                       /* dsa_mod_exp, */
    NULL,                       /* dsa_bn_mod_exp, */
    dsa_init,
    dsa_finish,
    DSA_FLAG_FIPS_METHOD,
    NULL,
    NULL,
    NULL
};

static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;

void DSA_set_default_method(const DSA_METHOD *meth)
{
    default_DSA_method = meth;
}

const DSA_METHOD *DSA_get_default_method(void)
{
    return default_DSA_method;
}

const DSA_METHOD *DSA_OpenSSL(void)
{
    return &openssl_dsa_meth;
}

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
{
    BIGNUM *kinv = NULL;
    BIGNUM *m, *blind, *blindm, *tmp;
    BN_CTX *ctx = NULL;
    int reason = ERR_R_BN_LIB;
    DSA_SIG *ret = NULL;
    int rv = 0;

    if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) {
        reason = DSA_R_MISSING_PARAMETERS;
        goto err;
    }

    ret = DSA_SIG_new();
    if (ret == NULL)
        goto err;
    ret->r = BN_new();
    ret->s = BN_new();
    if (ret->r == NULL || ret->s == NULL)
        goto err;

    ctx = BN_CTX_new();
    if (ctx == NULL)
        goto err;
    m = BN_CTX_get(ctx);
    blind = BN_CTX_get(ctx);
    blindm = BN_CTX_get(ctx);
    tmp = BN_CTX_get(ctx);
    if (tmp == NULL)
        goto err;

 redo:
    if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
        goto err;

    if (dlen > BN_num_bytes(dsa->q))
        /*
         * if the digest length is greater than the size of q use the
         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
         * 4.2
         */
        dlen = BN_num_bytes(dsa->q);
    if (BN_bin2bn(dgst, dlen, m) == NULL)
        goto err;

    /*
     * The normal signature calculation is:
     *
     *   s := k^-1 * (m + r * priv_key) mod q
     *
     * We will blind this to protect against side channel attacks
     *
     *   s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
     */

    /* Generate a blinding value */
    do {
        if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1,
                          BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
            goto err;
    } while (BN_is_zero(blind));
    BN_set_flags(blind, BN_FLG_CONSTTIME);
    BN_set_flags(blindm, BN_FLG_CONSTTIME);
    BN_set_flags(tmp, BN_FLG_CONSTTIME);

    /* tmp := blind * priv_key * r mod q */
    if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx))
        goto err;
    if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx))
        goto err;

    /* blindm := blind * m mod q */
    if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx))
        goto err;

    /* s : = (blind * priv_key * r) + (blind * m) mod q */
    if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q))
        goto err;

    /* s := s * k^-1 mod q */
    if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
        goto err;

    /* s:= s * blind^-1 mod q */
    if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL)
        goto err;
    if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx))
        goto err;

    /*
     * Redo if r or s is zero as required by FIPS 186-3: this is very
     * unlikely.
     */
    if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
        goto redo;

    rv = 1;

 err:
    if (rv == 0) {
        DSAerr(DSA_F_DSA_DO_SIGN, reason);
        DSA_SIG_free(ret);
        ret = NULL;
    }
    BN_CTX_free(ctx);
    BN_clear_free(kinv);
    return ret;
}

static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
                                    BIGNUM **kinvp, BIGNUM **rp)
{
    return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
}

static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
                          BIGNUM **kinvp, BIGNUM **rp,
                          const unsigned char *dgst, int dlen)
{
    BN_CTX *ctx = NULL;
    BIGNUM *k, *kinv = NULL, *r = *rp;
    BIGNUM *l, *m;
    int ret = 0;
    int q_bits;

    if (!dsa->p || !dsa->q || !dsa->g) {
        DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
        return 0;
    }

    k = BN_new();
    l = BN_new();
    m = BN_new();
    if (k == NULL || l == NULL || m == NULL)
        goto err;

    if (ctx_in == NULL) {
        if ((ctx = BN_CTX_new()) == NULL)
            goto err;
    } else
        ctx = ctx_in;

    /* Preallocate space */
    q_bits = BN_num_bits(dsa->q);
    if (!BN_set_bit(k, q_bits)
        || !BN_set_bit(l, q_bits)
        || !BN_set_bit(m, q_bits))
        goto err;

    /* Get random k */
    do {
        if (dgst != NULL) {
            /*
             * We calculate k from SHA512(private_key + H(message) + random).
             * This protects the private key from a weak PRNG.
             */
            if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
                                       dlen, ctx))
                goto err;
        } else if (!BN_priv_rand_range(k, dsa->q))
            goto err;
    } while (BN_is_zero(k));

    BN_set_flags(k, BN_FLG_CONSTTIME);

    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
        if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
                                    dsa->lock, dsa->p, ctx))
            goto err;
    }

    /* Compute r = (g^k mod p) mod q */

    /*
     * We do not want timing information to leak the length of k, so we
     * compute G^k using an equivalent scalar of fixed bit-length.
     *
     * We unconditionally perform both of these additions to prevent a
     * small timing information leakage.  We then choose the sum that is
     * one bit longer than the modulus.
     *
     * TODO: revisit the BN_copy aiming for a memory access agnostic
     * conditional copy.
     */
    if (!BN_add(l, k, dsa->q)
        || !BN_add(m, l, dsa->q)
        || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m))
        goto err;

    if ((dsa)->meth->bn_mod_exp != NULL) {
            if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
                                       dsa->method_mont_p))
                goto err;
    } else {
            if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
                goto err;
    }

    if (!BN_mod(r, r, dsa->q, ctx))
        goto err;

    /* Compute  part of 's = inv(k) (m + xr) mod q' */
    if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL)
        goto err;

    BN_clear_free(*kinvp);
    *kinvp = kinv;
    kinv = NULL;
    ret = 1;
 err:
    if (!ret)
        DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
    if (ctx != ctx_in)
        BN_CTX_free(ctx);
    BN_clear_free(k);
    BN_clear_free(l);
    BN_clear_free(m);
    return ret;
}

static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
                         DSA_SIG *sig, DSA *dsa)
{
    BN_CTX *ctx;
    BIGNUM *u1, *u2, *t1;
    BN_MONT_CTX *mont = NULL;
    const BIGNUM *r, *s;
    int ret = -1, i;
    if (!dsa->p || !dsa->q || !dsa->g) {
        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
        return -1;
    }

    i = BN_num_bits(dsa->q);
    /* fips 186-3 allows only different sizes for q */
    if (i != 160 && i != 224 && i != 256) {
        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
        return -1;
    }

    if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
        return -1;
    }
    u1 = BN_new();
    u2 = BN_new();
    t1 = BN_new();
    ctx = BN_CTX_new();
    if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
        goto err;

    DSA_SIG_get0(sig, &r, &s);

    if (BN_is_zero(r) || BN_is_negative(r) ||
        BN_ucmp(r, dsa->q) >= 0) {
        ret = 0;
        goto err;
    }
    if (BN_is_zero(s) || BN_is_negative(s) ||
        BN_ucmp(s, dsa->q) >= 0) {
        ret = 0;
        goto err;
    }

    /*
     * Calculate W = inv(S) mod Q save W in u2
     */
    if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
        goto err;

    /* save M in u1 */
    if (dgst_len > (i >> 3))
        /*
         * if the digest length is greater than the size of q use the
         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
         * 4.2
         */
        dgst_len = (i >> 3);
    if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
        goto err;

    /* u1 = M * w mod q */
    if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
        goto err;

    /* u2 = r * w mod q */
    if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
        goto err;

    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
        mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
                                      dsa->lock, dsa->p, ctx);
        if (!mont)
            goto err;
    }

    if (dsa->meth->dsa_mod_exp != NULL) {
        if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
                                    dsa->p, ctx, mont))
            goto err;
    } else {
        if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
                              mont))
            goto err;
    }

    /* let u1 = u1 mod q */
    if (!BN_mod(u1, t1, dsa->q, ctx))
        goto err;

    /*
     * V is now in u1.  If the signature is correct, it will be equal to R.
     */
    ret = (BN_ucmp(u1, r) == 0);

 err:
    if (ret < 0)
        DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
    BN_CTX_free(ctx);
    BN_free(u1);
    BN_free(u2);
    BN_free(t1);
    return ret;
}

static int dsa_init(DSA *dsa)
{
    dsa->flags |= DSA_FLAG_CACHE_MONT_P;
    return 1;
}

static int dsa_finish(DSA *dsa)
{
    BN_MONT_CTX_free(dsa->method_mont_p);
    return 1;
}

Coverage Report

Created: 2018-08-29 13:53

Line	Count	Source (jump to first uncovered line)
1		/*
2		* Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
3		*
4		* Licensed under the OpenSSL license (the "License"). You may not use
5		* this file except in compliance with the License. You can obtain a copy
6		* in the file LICENSE in the source distribution or at
7		* https://www.openssl.org/source/license.html
8		*/
9
10		#include <stdio.h>
11		#include "internal/cryptlib.h"
12		#include <openssl/bn.h>
13		#include <openssl/sha.h>
14		#include "dsa_locl.h"
15		#include <openssl/asn1.h>
16
17		static DSA_SIG dsa_do_sign(const unsigned char dgst, int dlen, DSA *dsa);
18		static int dsa_sign_setup_no_digest(DSA dsa, BN_CTX ctx_in, BIGNUM **kinvp,
19		BIGNUM **rp);
20		static int dsa_sign_setup(DSA dsa, BN_CTX ctx_in, BIGNUM **kinvp,
21		BIGNUM *rp, const unsigned char dgst, int dlen);
22		static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
23		DSA_SIG sig, DSA dsa);
24		static int dsa_init(DSA *dsa);
25		static int dsa_finish(DSA *dsa);
26
27		static DSA_METHOD openssl_dsa_meth = {
28		"OpenSSL DSA method",
29		dsa_do_sign,
30		dsa_sign_setup_no_digest,
31		dsa_do_verify,
32		NULL, /* dsa_mod_exp, */
33		NULL, /* dsa_bn_mod_exp, */
34		dsa_init,
35		dsa_finish,
36		DSA_FLAG_FIPS_METHOD,
37		NULL,
38		NULL,
39		NULL
40		};
41
42		static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
43
44		void DSA_set_default_method(const DSA_METHOD *meth)
45	0	{
46	0	default_DSA_method = meth;
47	0	}
48
49		const DSA_METHOD *DSA_get_default_method(void)
50	0	{
51	0	return default_DSA_method;
52	0	}
53
54		const DSA_METHOD *DSA_OpenSSL(void)
55	0	{
56	0	return &openssl_dsa_meth;
57	0	}
58
59		static DSA_SIG dsa_do_sign(const unsigned char dgst, int dlen, DSA *dsa)
60	0	{
61	0	BIGNUM *kinv = NULL;
62	0	BIGNUM m, blind, blindm, tmp;
63	0	BN_CTX *ctx = NULL;
64	0	int reason = ERR_R_BN_LIB;
65	0	DSA_SIG *ret = NULL;
66	0	int rv = 0;
67	0
68	0	if (dsa->p == NULL \|\| dsa->q == NULL \|\| dsa->g == NULL) {
69	0	reason = DSA_R_MISSING_PARAMETERS;
70	0	goto err;
71	0	}
72	0
73	0	ret = DSA_SIG_new();
74	0	if (ret == NULL)
75	0	goto err;
76	0	ret->r = BN_new();
77	0	ret->s = BN_new();
78	0	if (ret->r == NULL \|\| ret->s == NULL)
79	0	goto err;
80	0
81	0	ctx = BN_CTX_new();
82	0	if (ctx == NULL)
83	0	goto err;
84	0	m = BN_CTX_get(ctx);
85	0	blind = BN_CTX_get(ctx);
86	0	blindm = BN_CTX_get(ctx);
87	0	tmp = BN_CTX_get(ctx);
88	0	if (tmp == NULL)
89	0	goto err;
90	0
91	0	redo:
92	0	if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
93	0	goto err;
94	0
95	0	if (dlen > BN_num_bytes(dsa->q))
96	0	/*
97	0	* if the digest length is greater than the size of q use the
98	0	* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
99	0	* 4.2
100	0	*/
101	0	dlen = BN_num_bytes(dsa->q);
102	0	if (BN_bin2bn(dgst, dlen, m) == NULL)
103	0	goto err;
104	0
105	0	/*
106	0	* The normal signature calculation is:
107	0	*
108	0	* s := k^-1 * (m + r * priv_key) mod q
109	0	*
110	0	* We will blind this to protect against side channel attacks
111	0	*
112	0	* s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
113	0	*/
114	0
115	0	/* Generate a blinding value */
116	0	do {
117	0	if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1,
118	0	BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
119	0	goto err;
120	0	} while (BN_is_zero(blind));
121	0	BN_set_flags(blind, BN_FLG_CONSTTIME);
122	0	BN_set_flags(blindm, BN_FLG_CONSTTIME);
123	0	BN_set_flags(tmp, BN_FLG_CONSTTIME);
124	0
125	0	/* tmp := blind * priv_key * r mod q */
126	0	if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx))
127	0	goto err;
128	0	if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx))
129	0	goto err;
130	0
131	0	/* blindm := blind * m mod q */
132	0	if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx))
133	0	goto err;
134	0
135	0	/* s : = (blind * priv_key * r) + (blind * m) mod q */
136	0	if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q))
137	0	goto err;
138	0
139	0	/* s := s * k^-1 mod q */
140	0	if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
141	0	goto err;
142	0
143	0	/* s:= s * blind^-1 mod q */
144	0	if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL)
145	0	goto err;
146	0	if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx))
147	0	goto err;
148	0
149	0	/*
150	0	* Redo if r or s is zero as required by FIPS 186-3: this is very
151	0	* unlikely.
152	0	*/
153	0	if (BN_is_zero(ret->r) \|\| BN_is_zero(ret->s))
154	0	goto redo;
155	0
156	0	rv = 1;
157	0
158	0	err:
159	0	if (rv == 0) {
160	0	DSAerr(DSA_F_DSA_DO_SIGN, reason);
161	0	DSA_SIG_free(ret);
162	0	ret = NULL;
163	0	}
164	0	BN_CTX_free(ctx);
165	0	BN_clear_free(kinv);
166	0	return ret;
167	0	}
168
169		static int dsa_sign_setup_no_digest(DSA dsa, BN_CTX ctx_in,
170		BIGNUM kinvp, BIGNUM rp)
171	0	{
172	0	return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
173	0	}
174
175		static int dsa_sign_setup(DSA dsa, BN_CTX ctx_in,
176		BIGNUM kinvp, BIGNUM rp,
177		const unsigned char *dgst, int dlen)
178	0	{
179	0	BN_CTX *ctx = NULL;
180	0	BIGNUM k, kinv = NULL, r = rp;
181	0	BIGNUM l, m;
182	0	int ret = 0;
183	0	int q_bits;
184	0
185	0	if (!dsa->p \|\| !dsa->q \|\| !dsa->g) {
186	0	DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
187	0	return 0;
188	0	}
189	0
190	0	k = BN_new();
191	0	l = BN_new();
192	0	m = BN_new();
193	0	if (k == NULL \|\| l == NULL \|\| m == NULL)
194	0	goto err;
195	0
196	0	if (ctx_in == NULL) {
197	0	if ((ctx = BN_CTX_new()) == NULL)
198	0	goto err;
199	0	} else
200	0	ctx = ctx_in;
201	0
202	0	/* Preallocate space */
203	0	q_bits = BN_num_bits(dsa->q);
204	0	if (!BN_set_bit(k, q_bits)
205	0	\|\| !BN_set_bit(l, q_bits)
206	0	\|\| !BN_set_bit(m, q_bits))
207	0	goto err;
208	0
209	0	/* Get random k */
210	0	do {
211	0	if (dgst != NULL) {
212	0	/*
213	0	* We calculate k from SHA512(private_key + H(message) + random).
214	0	* This protects the private key from a weak PRNG.
215	0	*/
216	0	if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
217	0	dlen, ctx))
218	0	goto err;
219	0	} else if (!BN_priv_rand_range(k, dsa->q))
220	0	goto err;
221	0	} while (BN_is_zero(k));
222	0
223	0	BN_set_flags(k, BN_FLG_CONSTTIME);
224	0
225	0	if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
226	0	if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
227	0	dsa->lock, dsa->p, ctx))
228	0	goto err;
229	0	}
230	0
231	0	/* Compute r = (g^k mod p) mod q */
232	0
233	0	/*
234	0	* We do not want timing information to leak the length of k, so we
235	0	* compute G^k using an equivalent scalar of fixed bit-length.
236	0	*
237	0	* We unconditionally perform both of these additions to prevent a
238	0	* small timing information leakage. We then choose the sum that is
239	0	* one bit longer than the modulus.
240	0	*
241	0	* TODO: revisit the BN_copy aiming for a memory access agnostic
242	0	* conditional copy.
243	0	*/
244	0	if (!BN_add(l, k, dsa->q)
245	0	\|\| !BN_add(m, l, dsa->q)
246	0	\|\| !BN_copy(k, BN_num_bits(l) > q_bits ? l : m))
247	0	goto err;
248	0
249	0	if ((dsa)->meth->bn_mod_exp != NULL) {
250	0	if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
251	0	dsa->method_mont_p))
252	0	goto err;
253	0	} else {
254	0	if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
255	0	goto err;
256	0	}
257	0
258	0	if (!BN_mod(r, r, dsa->q, ctx))
259	0	goto err;
260	0
261	0	/* Compute part of 's = inv(k) (m + xr) mod q' */
262	0	if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL)
263	0	goto err;
264	0
265	0	BN_clear_free(*kinvp);
266	0	*kinvp = kinv;
267	0	kinv = NULL;
268	0	ret = 1;
269	0	err:
270	0	if (!ret)
271	0	DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
272	0	if (ctx != ctx_in)
273	0	BN_CTX_free(ctx);
274	0	BN_clear_free(k);
275	0	BN_clear_free(l);
276	0	BN_clear_free(m);
277	0	return ret;
278	0	}
279
280		static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
281		DSA_SIG sig, DSA dsa)
282	0	{
283	0	BN_CTX *ctx;
284	0	BIGNUM u1, u2, *t1;
285	0	BN_MONT_CTX *mont = NULL;
286	0	const BIGNUM r, s;
287	0	int ret = -1, i;
288	0	if (!dsa->p \|\| !dsa->q \|\| !dsa->g) {
289	0	DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
290	0	return -1;
291	0	}
292	0
293	0	i = BN_num_bits(dsa->q);
294	0	/* fips 186-3 allows only different sizes for q */
295	0	if (i != 160 && i != 224 && i != 256) {
296	0	DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
297	0	return -1;
298	0	}
299	0
300	0	if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
301	0	DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
302	0	return -1;
303	0	}
304	0	u1 = BN_new();
305	0	u2 = BN_new();
306	0	t1 = BN_new();
307	0	ctx = BN_CTX_new();
308	0	if (u1 == NULL \|\| u2 == NULL \|\| t1 == NULL \|\| ctx == NULL)
309	0	goto err;
310	0
311	0	DSA_SIG_get0(sig, &r, &s);
312	0
313	0	if (BN_is_zero(r) \|\| BN_is_negative(r) \|\|
314	0	BN_ucmp(r, dsa->q) >= 0) {
315	0	ret = 0;
316	0	goto err;
317	0	}
318	0	if (BN_is_zero(s) \|\| BN_is_negative(s) \|\|
319	0	BN_ucmp(s, dsa->q) >= 0) {
320	0	ret = 0;
321	0	goto err;
322	0	}
323	0
324	0	/*
325	0	* Calculate W = inv(S) mod Q save W in u2
326	0	*/
327	0	if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
328	0	goto err;
329	0
330	0	/* save M in u1 */
331	0	if (dgst_len > (i >> 3))
332	0	/*
333	0	* if the digest length is greater than the size of q use the
334	0	* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
335	0	* 4.2
336	0	*/
337	0	dgst_len = (i >> 3);
338	0	if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
339	0	goto err;
340	0
341	0	/* u1 = M * w mod q */
342	0	if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
343	0	goto err;
344	0
345	0	/* u2 = r * w mod q */
346	0	if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
347	0	goto err;
348	0
349	0	if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
350	0	mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
351	0	dsa->lock, dsa->p, ctx);
352	0	if (!mont)
353	0	goto err;
354	0	}
355	0
356	0	if (dsa->meth->dsa_mod_exp != NULL) {
357	0	if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
358	0	dsa->p, ctx, mont))
359	0	goto err;
360	0	} else {
361	0	if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
362	0	mont))
363	0	goto err;
364	0	}
365	0
366	0	/* let u1 = u1 mod q */
367	0	if (!BN_mod(u1, t1, dsa->q, ctx))
368	0	goto err;
369	0
370	0	/*
371	0	* V is now in u1. If the signature is correct, it will be equal to R.
372	0	*/
373	0	ret = (BN_ucmp(u1, r) == 0);
374	0
375	0	err:
376	0	if (ret < 0)
377	0	DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
378	0	BN_CTX_free(ctx);
379	0	BN_free(u1);
380	0	BN_free(u2);
381	0	BN_free(t1);
382	0	return ret;
383	0	}
384
385		static int dsa_init(DSA *dsa)
386	0	{
387	0	dsa->flags \|= DSA_FLAG_CACHE_MONT_P;
388	0	return 1;
389	0	}
390
391		static int dsa_finish(DSA *dsa)
392	0	{
393	0	BN_MONT_CTX_free(dsa->method_mont_p);
394	0	return 1;
395	0	}