/src/openssl31/crypto/dsa/dsa_ossl.c

Source (jump to first uncovered line)
/*
 * Copyright 1995-2024 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the Apache License 2.0 (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
 */

/*
 * DSA low level APIs are deprecated for public use, but still ok for
 * internal use.
 */
#include "internal/deprecated.h"

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

#define MIN_DSA_SIGN_QBITS   128
#define MAX_DSA_SIGN_RETRIES 8

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 BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
                                      BN_CTX *ctx);

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;

#ifndef FIPS_MODULE
void DSA_set_default_method(const DSA_METHOD *meth)
{
    default_DSA_method = meth;
}
#endif /* FIPS_MODULE */

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

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

DSA_SIG *ossl_dsa_do_sign_int(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;
    int retries = 0;

    if (dsa->params.p == NULL
        || dsa->params.q == NULL
        || dsa->params.g == NULL) {
        reason = DSA_R_MISSING_PARAMETERS;
        goto err;
    }
    if (dsa->priv_key == NULL) {
        reason = DSA_R_MISSING_PRIVATE_KEY;
        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_ex(dsa->libctx);
    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->params.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->params.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
     * The size of q is tested in dsa_sign_setup() so there should not be an infinite loop here.
     */
    do {
        if (!BN_priv_rand_ex(blind, BN_num_bits(dsa->params.q) - 1,
                             BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, 0, ctx))
            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->params.q, ctx))
        goto err;
    if (!BN_mod_mul(tmp, tmp, ret->r, dsa->params.q, ctx))
        goto err;

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

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

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

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

    /*
     * Redo if r or s is zero as required by FIPS 186-4: Section 4.6
     * This is very unlikely.
     * Limit the retries so there is no possibility of an infinite
     * loop for bad domain parameter values.
     */
    if (BN_is_zero(ret->r) || BN_is_zero(ret->s)) {
        if (retries++ > MAX_DSA_SIGN_RETRIES) {
            reason = DSA_R_TOO_MANY_RETRIES;
            goto err;
        }
        goto redo;
    }
    rv = 1;
 err:
    if (rv == 0) {
        ERR_raise(ERR_LIB_DSA, reason);
        DSA_SIG_free(ret);
        ret = NULL;
    }
    BN_CTX_free(ctx);
    BN_clear_free(kinv);
    return ret;
}

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
{
    return ossl_dsa_do_sign_int(dgst, dlen, dsa);
}

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;
    int ret = 0;
    int q_bits, q_words;

    if (!dsa->params.p || !dsa->params.q || !dsa->params.g) {
        ERR_raise(ERR_LIB_DSA, DSA_R_MISSING_PARAMETERS);
        return 0;
    }

    /* Reject obviously invalid parameters */
    if (BN_is_zero(dsa->params.p)
        || BN_is_zero(dsa->params.q)
        || BN_is_zero(dsa->params.g)
        || BN_is_negative(dsa->params.p)
        || BN_is_negative(dsa->params.q)
        || BN_is_negative(dsa->params.g)) {
        ERR_raise(ERR_LIB_DSA, DSA_R_INVALID_PARAMETERS);
        return 0;
    }
    if (dsa->priv_key == NULL) {
        ERR_raise(ERR_LIB_DSA, DSA_R_MISSING_PRIVATE_KEY);
        return 0;
    }
    k = BN_new();
    l = BN_new();
    if (k == NULL || l == NULL)
        goto err;

    if (ctx_in == NULL) {
        /* if you don't pass in ctx_in you get a default libctx */
        if ((ctx = BN_CTX_new_ex(NULL)) == NULL)
            goto err;
    } else
        ctx = ctx_in;

    /* Preallocate space */
    q_bits = BN_num_bits(dsa->params.q);
    q_words = bn_get_top(dsa->params.q);
    if (q_bits < MIN_DSA_SIGN_QBITS
        || !bn_wexpand(k, q_words + 2)
        || !bn_wexpand(l, q_words + 2))
        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 (!ossl_bn_gen_dsa_nonce_fixed_top(k, dsa->params.q,
                                                 dsa->priv_key, dgst,
                                                 dlen, ctx))
                goto err;
        } else if (!ossl_bn_priv_rand_range_fixed_top(k, dsa->params.q, 0, ctx))
            goto err;
    } while (ossl_bn_is_word_fixed_top(k, 0));

    BN_set_flags(k, BN_FLG_CONSTTIME);
    BN_set_flags(l, BN_FLG_CONSTTIME);

    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
        if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
                                    dsa->lock, dsa->params.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.
     *
     * There are some concerns about the efficacy of doing this.  More
     * specifically refer to the discussion starting with:
     *     https://github.com/openssl/openssl/pull/7486#discussion_r228323705
     * The fix is to rework BN so these gymnastics aren't required.
     */
    if (!BN_add(l, k, dsa->params.q)
        || !BN_add(k, l, dsa->params.q))
        goto err;

    BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);

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

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

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

    BN_clear_free(*kinvp);
    *kinvp = kinv;
    kinv = NULL;
    ret = 1;
 err:
    if (!ret)
        ERR_raise(ERR_LIB_DSA, ERR_R_BN_LIB);
    if (ctx != ctx_in)
        BN_CTX_free(ctx);
    BN_clear_free(k);
    BN_clear_free(l);
    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->params.p == NULL
        || dsa->params.q == NULL
        || dsa->params.g == NULL) {
        ERR_raise(ERR_LIB_DSA, DSA_R_MISSING_PARAMETERS);
        return -1;
    }

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

    if (BN_num_bits(dsa->params.p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
        ERR_raise(ERR_LIB_DSA, DSA_R_MODULUS_TOO_LARGE);
        return -1;
    }
    u1 = BN_new();
    u2 = BN_new();
    t1 = BN_new();
    ctx = BN_CTX_new_ex(NULL); /* verify does not need a libctx */
    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->params.q) >= 0) {
        ret = 0;
        goto err;
    }
    if (BN_is_zero(s) || BN_is_negative(s) ||
        BN_ucmp(s, dsa->params.q) >= 0) {
        ret = 0;
        goto err;
    }

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

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

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

    /* let u1 = u1 mod q */
    if (!BN_mod(u1, t1, dsa->params.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)
        ERR_raise(ERR_LIB_DSA, 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;
    dsa->dirty_cnt++;
    return 1;
}

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

/*
 * Compute the inverse of k modulo q.
 * Since q is prime, Fermat's Little Theorem applies, which reduces this to
 * mod-exp operation.  Both the exponent and modulus are public information
 * so a mod-exp that doesn't leak the base is sufficient.  A newly allocated
 * BIGNUM is returned which the caller must free.
 */
static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
                                      BN_CTX *ctx)
{
    BIGNUM *res = NULL;
    BIGNUM *r, *e;

    if ((r = BN_new()) == NULL)
        return NULL;

    BN_CTX_start(ctx);
    if ((e = BN_CTX_get(ctx)) != NULL
            && BN_set_word(r, 2)
            && BN_sub(e, q, r)
            && BN_mod_exp_mont(r, k, e, q, ctx, NULL))
        res = r;
    else
        BN_free(r);
    BN_CTX_end(ctx);
    return res;
}

Coverage Report

Created: 2025-06-13 06:58

Line	Count	Source (jump to first uncovered line)
1		/*
2		* Copyright 1995-2024 The OpenSSL Project Authors. All Rights Reserved.
3		*
4		* Licensed under the Apache License 2.0 (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		/*
11		* DSA low level APIs are deprecated for public use, but still ok for
12		* internal use.
13		*/
14		#include "internal/deprecated.h"
15
16		#include <stdio.h>
17		#include "internal/cryptlib.h"
18		#include "crypto/bn.h"
19		#include <openssl/bn.h>
20		#include <openssl/sha.h>
21		#include "dsa_local.h"
22		#include <openssl/asn1.h>
23
24	0	#define MIN_DSA_SIGN_QBITS 128
25	0	#define MAX_DSA_SIGN_RETRIES 8
26
27		static DSA_SIG dsa_do_sign(const unsigned char dgst, int dlen, DSA *dsa);
28		static int dsa_sign_setup_no_digest(DSA dsa, BN_CTX ctx_in, BIGNUM **kinvp,
29		BIGNUM **rp);
30		static int dsa_sign_setup(DSA dsa, BN_CTX ctx_in, BIGNUM **kinvp,
31		BIGNUM *rp, const unsigned char dgst, int dlen);
32		static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
33		DSA_SIG sig, DSA dsa);
34		static int dsa_init(DSA *dsa);
35		static int dsa_finish(DSA *dsa);
36		static BIGNUM dsa_mod_inverse_fermat(const BIGNUM k, const BIGNUM *q,
37		BN_CTX *ctx);
38
39		static DSA_METHOD openssl_dsa_meth = {
40		"OpenSSL DSA method",
41		dsa_do_sign,
42		dsa_sign_setup_no_digest,
43		dsa_do_verify,
44		NULL, /* dsa_mod_exp, */
45		NULL, /* dsa_bn_mod_exp, */
46		dsa_init,
47		dsa_finish,
48		DSA_FLAG_FIPS_METHOD,
49		NULL,
50		NULL,
51		NULL
52		};
53
54		static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
55
56		#ifndef FIPS_MODULE
57		void DSA_set_default_method(const DSA_METHOD *meth)
58	0	{
59	0	default_DSA_method = meth;
60	0	}
61		#endif /* FIPS_MODULE */
62
63		const DSA_METHOD *DSA_get_default_method(void)
64	403k	{
65	403k	return default_DSA_method;
66	403k	}
67
68		const DSA_METHOD *DSA_OpenSSL(void)
69	90.3k	{
70	90.3k	return &openssl_dsa_meth;
71	90.3k	}
72
73		DSA_SIG ossl_dsa_do_sign_int(const unsigned char dgst, int dlen, DSA *dsa)
74	0	{
75	0	BIGNUM *kinv = NULL;
76	0	BIGNUM m, blind, blindm, tmp;
77	0	BN_CTX *ctx = NULL;
78	0	int reason = ERR_R_BN_LIB;
79	0	DSA_SIG *ret = NULL;
80	0	int rv = 0;
81	0	int retries = 0;
82
83	0	if (dsa->params.p == NULL
84	0	\|\| dsa->params.q == NULL
85	0	\|\| dsa->params.g == NULL) {
86	0	reason = DSA_R_MISSING_PARAMETERS;
87	0	goto err;
88	0	}
89	0	if (dsa->priv_key == NULL) {
90	0	reason = DSA_R_MISSING_PRIVATE_KEY;
91	0	goto err;
92	0	}
93
94	0	ret = DSA_SIG_new();
95	0	if (ret == NULL)
96	0	goto err;
97	0	ret->r = BN_new();
98	0	ret->s = BN_new();
99	0	if (ret->r == NULL \|\| ret->s == NULL)
100	0	goto err;
101
102	0	ctx = BN_CTX_new_ex(dsa->libctx);
103	0	if (ctx == NULL)
104	0	goto err;
105	0	m = BN_CTX_get(ctx);
106	0	blind = BN_CTX_get(ctx);
107	0	blindm = BN_CTX_get(ctx);
108	0	tmp = BN_CTX_get(ctx);
109	0	if (tmp == NULL)
110	0	goto err;
111
112	0	redo:
113	0	if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
114	0	goto err;
115
116	0	if (dlen > BN_num_bytes(dsa->params.q))
117		/*
118		* if the digest length is greater than the size of q use the
119		* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
120		* 4.2
121		*/
122	0	dlen = BN_num_bytes(dsa->params.q);
123	0	if (BN_bin2bn(dgst, dlen, m) == NULL)
124	0	goto err;
125
126		/*
127		* The normal signature calculation is:
128		*
129		* s := k^-1 * (m + r * priv_key) mod q
130		*
131		* We will blind this to protect against side channel attacks
132		*
133		* s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
134		*/
135
136		/*
137		* Generate a blinding value
138		* The size of q is tested in dsa_sign_setup() so there should not be an infinite loop here.
139		*/
140	0	do {
141	0	if (!BN_priv_rand_ex(blind, BN_num_bits(dsa->params.q) - 1,
142	0	BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, 0, ctx))
143	0	goto err;
144	0	} while (BN_is_zero(blind));
145	0	BN_set_flags(blind, BN_FLG_CONSTTIME);
146	0	BN_set_flags(blindm, BN_FLG_CONSTTIME);
147	0	BN_set_flags(tmp, BN_FLG_CONSTTIME);
148
149		/* tmp := blind * priv_key * r mod q */
150	0	if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->params.q, ctx))
151	0	goto err;
152	0	if (!BN_mod_mul(tmp, tmp, ret->r, dsa->params.q, ctx))
153	0	goto err;
154
155		/* blindm := blind * m mod q */
156	0	if (!BN_mod_mul(blindm, blind, m, dsa->params.q, ctx))
157	0	goto err;
158
159		/* s : = (blind * priv_key * r) + (blind * m) mod q */
160	0	if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->params.q))
161	0	goto err;
162
163		/* s := s * k^-1 mod q */
164	0	if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->params.q, ctx))
165	0	goto err;
166
167		/* s:= s * blind^-1 mod q */
168	0	if (BN_mod_inverse(blind, blind, dsa->params.q, ctx) == NULL)
169	0	goto err;
170	0	if (!BN_mod_mul(ret->s, ret->s, blind, dsa->params.q, ctx))
171	0	goto err;
172
173		/*
174		* Redo if r or s is zero as required by FIPS 186-4: Section 4.6
175		* This is very unlikely.
176		* Limit the retries so there is no possibility of an infinite
177		* loop for bad domain parameter values.
178		*/
179	0	if (BN_is_zero(ret->r) \|\| BN_is_zero(ret->s)) {
180	0	if (retries++ > MAX_DSA_SIGN_RETRIES) {
181	0	reason = DSA_R_TOO_MANY_RETRIES;
182	0	goto err;
183	0	}
184	0	goto redo;
185	0	}
186	0	rv = 1;
187	0	err:
188	0	if (rv == 0) {
189	0	ERR_raise(ERR_LIB_DSA, reason);
190	0	DSA_SIG_free(ret);
191	0	ret = NULL;
192	0	}
193	0	BN_CTX_free(ctx);
194	0	BN_clear_free(kinv);
195	0	return ret;
196	0	}
197
198		static DSA_SIG dsa_do_sign(const unsigned char dgst, int dlen, DSA *dsa)
199	0	{
200	0	return ossl_dsa_do_sign_int(dgst, dlen, dsa);
201	0	}
202
203		static int dsa_sign_setup_no_digest(DSA dsa, BN_CTX ctx_in,
204		BIGNUM kinvp, BIGNUM rp)
205	0	{
206	0	return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
207	0	}
208
209		static int dsa_sign_setup(DSA dsa, BN_CTX ctx_in,
210		BIGNUM kinvp, BIGNUM rp,
211		const unsigned char *dgst, int dlen)
212	0	{
213	0	BN_CTX *ctx = NULL;
214	0	BIGNUM k, kinv = NULL, r = rp;
215	0	BIGNUM *l;
216	0	int ret = 0;
217	0	int q_bits, q_words;
218
219	0	if (!dsa->params.p \|\| !dsa->params.q \|\| !dsa->params.g) {
220	0	ERR_raise(ERR_LIB_DSA, DSA_R_MISSING_PARAMETERS);
221	0	return 0;
222	0	}
223
224		/* Reject obviously invalid parameters */
225	0	if (BN_is_zero(dsa->params.p)
226	0	\|\| BN_is_zero(dsa->params.q)
227	0	\|\| BN_is_zero(dsa->params.g)
228	0	\|\| BN_is_negative(dsa->params.p)
229	0	\|\| BN_is_negative(dsa->params.q)
230	0	\|\| BN_is_negative(dsa->params.g)) {
231	0	ERR_raise(ERR_LIB_DSA, DSA_R_INVALID_PARAMETERS);
232	0	return 0;
233	0	}
234	0	if (dsa->priv_key == NULL) {
235	0	ERR_raise(ERR_LIB_DSA, DSA_R_MISSING_PRIVATE_KEY);
236	0	return 0;
237	0	}
238	0	k = BN_new();
239	0	l = BN_new();
240	0	if (k == NULL \|\| l == NULL)
241	0	goto err;
242
243	0	if (ctx_in == NULL) {
244		/* if you don't pass in ctx_in you get a default libctx */
245	0	if ((ctx = BN_CTX_new_ex(NULL)) == NULL)
246	0	goto err;
247	0	} else
248	0	ctx = ctx_in;
249
250		/* Preallocate space */
251	0	q_bits = BN_num_bits(dsa->params.q);
252	0	q_words = bn_get_top(dsa->params.q);
253	0	if (q_bits < MIN_DSA_SIGN_QBITS
254	0	\|\| !bn_wexpand(k, q_words + 2)
255	0	\|\| !bn_wexpand(l, q_words + 2))
256	0	goto err;
257
258		/* Get random k */
259	0	do {
260	0	if (dgst != NULL) {
261		/*
262		* We calculate k from SHA512(private_key + H(message) + random).
263		* This protects the private key from a weak PRNG.
264		*/
265	0	if (!ossl_bn_gen_dsa_nonce_fixed_top(k, dsa->params.q,
266	0	dsa->priv_key, dgst,
267	0	dlen, ctx))
268	0	goto err;
269	0	} else if (!ossl_bn_priv_rand_range_fixed_top(k, dsa->params.q, 0, ctx))
270	0	goto err;
271	0	} while (ossl_bn_is_word_fixed_top(k, 0));
272
273	0	BN_set_flags(k, BN_FLG_CONSTTIME);
274	0	BN_set_flags(l, BN_FLG_CONSTTIME);
275
276	0	if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
277	0	if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
278	0	dsa->lock, dsa->params.p, ctx))
279	0	goto err;
280	0	}
281
282		/* Compute r = (g^k mod p) mod q */
283
284		/*
285		* We do not want timing information to leak the length of k, so we
286		* compute G^k using an equivalent scalar of fixed bit-length.
287		*
288		* We unconditionally perform both of these additions to prevent a
289		* small timing information leakage. We then choose the sum that is
290		* one bit longer than the modulus.
291		*
292		* There are some concerns about the efficacy of doing this. More
293		* specifically refer to the discussion starting with:
294		* https://github.com/openssl/openssl/pull/7486#discussion_r228323705
295		* The fix is to rework BN so these gymnastics aren't required.
296		*/
297	0	if (!BN_add(l, k, dsa->params.q)
298	0	\|\| !BN_add(k, l, dsa->params.q))
299	0	goto err;
300
301	0	BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);
302
303	0	if ((dsa)->meth->bn_mod_exp != NULL) {
304	0	if (!dsa->meth->bn_mod_exp(dsa, r, dsa->params.g, k, dsa->params.p,
305	0	ctx, dsa->method_mont_p))
306	0	goto err;
307	0	} else {
308	0	if (!BN_mod_exp_mont(r, dsa->params.g, k, dsa->params.p, ctx,
309	0	dsa->method_mont_p))
310	0	goto err;
311	0	}
312
313	0	if (!BN_mod(r, r, dsa->params.q, ctx))
314	0	goto err;
315
316		/* Compute part of 's = inv(k) (m + xr) mod q' */
317	0	if ((kinv = dsa_mod_inverse_fermat(k, dsa->params.q, ctx)) == NULL)
318	0	goto err;
319
320	0	BN_clear_free(*kinvp);
321	0	*kinvp = kinv;
322	0	kinv = NULL;
323	0	ret = 1;
324	0	err:
325	0	if (!ret)
326	0	ERR_raise(ERR_LIB_DSA, ERR_R_BN_LIB);
327	0	if (ctx != ctx_in)
328	0	BN_CTX_free(ctx);
329	0	BN_clear_free(k);
330	0	BN_clear_free(l);
331	0	return ret;
332	0	}
333
334		static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
335		DSA_SIG sig, DSA dsa)
336	1.25k	{
337	1.25k	BN_CTX *ctx;
338	1.25k	BIGNUM u1, u2, *t1;
339	1.25k	BN_MONT_CTX *mont = NULL;
340	1.25k	const BIGNUM r, s;
341	1.25k	int ret = -1, i;
342
343	1.25k	if (dsa->params.p == NULL
344	1.25k	\|\| dsa->params.q == NULL
345	1.25k	\|\| dsa->params.g == NULL) {
346	0	ERR_raise(ERR_LIB_DSA, DSA_R_MISSING_PARAMETERS);
347	0	return -1;
348	0	}
349
350	1.25k	i = BN_num_bits(dsa->params.q);
351		/* fips 186-3 allows only different sizes for q */
352	1.25k	if (i != 160 && i != 224 && i != 256) {
353	20	ERR_raise(ERR_LIB_DSA, DSA_R_BAD_Q_VALUE);
354	20	return -1;
355	20	}
356
357	1.23k	if (BN_num_bits(dsa->params.p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
358	0	ERR_raise(ERR_LIB_DSA, DSA_R_MODULUS_TOO_LARGE);
359	0	return -1;
360	0	}
361	1.23k	u1 = BN_new();
362	1.23k	u2 = BN_new();
363	1.23k	t1 = BN_new();
364	1.23k	ctx = BN_CTX_new_ex(NULL); /* verify does not need a libctx */
365	1.23k	if (u1 == NULL \|\| u2 == NULL \|\| t1 == NULL \|\| ctx == NULL)
366	0	goto err;
367
368	1.23k	DSA_SIG_get0(sig, &r, &s);
369
370	1.23k	if (BN_is_zero(r) \|\| BN_is_negative(r) \|\|
371	1.23k	BN_ucmp(r, dsa->params.q) >= 0) {
372	4	ret = 0;
373	4	goto err;
374	4	}
375	1.23k	if (BN_is_zero(s) \|\| BN_is_negative(s) \|\|
376	1.23k	BN_ucmp(s, dsa->params.q) >= 0) {
377	8	ret = 0;
378	8	goto err;
379	8	}
380
381		/*
382		* Calculate W = inv(S) mod Q save W in u2
383		*/
384	1.22k	if ((BN_mod_inverse(u2, s, dsa->params.q, ctx)) == NULL)
385	52	goto err;
386
387		/* save M in u1 */
388	1.17k	if (dgst_len > (i >> 3))
389		/*
390		* if the digest length is greater than the size of q use the
391		* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
392		* 4.2
393		*/
394	530	dgst_len = (i >> 3);
395	1.17k	if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
396	0	goto err;
397
398		/* u1 = M * w mod q */
399	1.17k	if (!BN_mod_mul(u1, u1, u2, dsa->params.q, ctx))
400	0	goto err;
401
402		/* u2 = r * w mod q */
403	1.17k	if (!BN_mod_mul(u2, r, u2, dsa->params.q, ctx))
404	0	goto err;
405
406	1.17k	if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
407	1.17k	mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
408	1.17k	dsa->lock, dsa->params.p, ctx);
409	1.17k	if (!mont)
410	41	goto err;
411	1.17k	}
412
413	1.13k	if (dsa->meth->dsa_mod_exp != NULL) {
414	0	if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->params.g, u1, dsa->pub_key, u2,
415	0	dsa->params.p, ctx, mont))
416	0	goto err;
417	1.13k	} else {
418	1.13k	if (!BN_mod_exp2_mont(t1, dsa->params.g, u1, dsa->pub_key, u2,
419	1.13k	dsa->params.p, ctx, mont))
420	0	goto err;
421	1.13k	}
422
423		/* let u1 = u1 mod q */
424	1.13k	if (!BN_mod(u1, t1, dsa->params.q, ctx))
425	0	goto err;
426
427		/*
428		* V is now in u1. If the signature is correct, it will be equal to R.
429		*/
430	1.13k	ret = (BN_ucmp(u1, r) == 0);
431
432	1.23k	err:
433	1.23k	if (ret < 0)
434	1.23k	ERR_raise(ERR_LIB_DSA, ERR_R_BN_LIB);
435	1.23k	BN_CTX_free(ctx);
436	1.23k	BN_free(u1);
437	1.23k	BN_free(u2);
438	1.23k	BN_free(t1);
439	1.23k	return ret;
440	1.13k	}
441
442		static int dsa_init(DSA *dsa)
443	403k	{
444	403k	dsa->flags \|= DSA_FLAG_CACHE_MONT_P;
445	403k	dsa->dirty_cnt++;
446	403k	return 1;
447	403k	}
448
449		static int dsa_finish(DSA *dsa)
450	403k	{
451	403k	BN_MONT_CTX_free(dsa->method_mont_p);
452	403k	return 1;
453	403k	}
454
455		/*
456		* Compute the inverse of k modulo q.
457		* Since q is prime, Fermat's Little Theorem applies, which reduces this to
458		* mod-exp operation. Both the exponent and modulus are public information
459		* so a mod-exp that doesn't leak the base is sufficient. A newly allocated
460		* BIGNUM is returned which the caller must free.
461		*/
462		static BIGNUM dsa_mod_inverse_fermat(const BIGNUM k, const BIGNUM *q,
463		BN_CTX *ctx)
464	0	{
465	0	BIGNUM *res = NULL;
466	0	BIGNUM r, e;
467
468	0	if ((r = BN_new()) == NULL)
469	0	return NULL;
470
471	0	BN_CTX_start(ctx);
472	0	if ((e = BN_CTX_get(ctx)) != NULL
473	0	&& BN_set_word(r, 2)
474	0	&& BN_sub(e, q, r)
475	0	&& BN_mod_exp_mont(r, k, e, q, ctx, NULL))
476	0	res = r;
477	0	else
478	0	BN_free(r);
479	0	BN_CTX_end(ctx);
480	0	return res;
481	0	}