[thirdparty/openssl.git] / crypto / dsa / dsa_ossl.c

/*
 * Copyright 1995-2018 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
 */

#include <stdio.h>
#include "internal/cryptlib.h"
#include "internal/bn_int.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 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;

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;
    int ret = 0;
    int q_bits, q_words;

    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();
    if (k == NULL || l == 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);
    q_words = bn_get_top(dsa->q);
    if (!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 (!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);
    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->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
     * specificly 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->q)
        || !BN_add(k, l, dsa->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->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 = dsa_mod_inverse_fermat(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);
    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;
}

/*
 * 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;
}
Commit	Line	Data
d2e9e320	1	/*
1212818e	2	* Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
c0711f7f	3	*
3cdbea65	4	* Licensed under the Apache License 2.0 (the "License"). You may not use
d2e9e320 RS	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
c0711f7f DSH	8	*/
c0711f7f DSH	9
c0711f7f	10	#include <stdio.h>
b39fc560	11	#include "internal/cryptlib.h"
a9cfb8c2	12	#include "internal/bn_int.h"
c0711f7f	13	#include <openssl/bn.h>
357d5de5	14	#include <openssl/sha.h>
1258396d	15	#include "dsa_locl.h"
c0711f7f DSH	16	#include <openssl/asn1.h>
	17
	18	static DSA_SIG dsa_do_sign(const unsigned char dgst, int dlen, DSA *dsa);
0f113f3e MC	19	static int dsa_sign_setup_no_digest(DSA dsa, BN_CTX ctx_in, BIGNUM **kinvp,
	20	BIGNUM **rp);
	21	static int dsa_sign_setup(DSA dsa, BN_CTX ctx_in, BIGNUM **kinvp,
	22	BIGNUM *rp, const unsigned char dgst, int dlen);
	23	static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
	24	DSA_SIG sig, DSA dsa);
c0711f7f DSH	25	static int dsa_init(DSA *dsa);
c0711f7f DSH	26	static int dsa_finish(DSA *dsa);
415c3356 P	27	static BIGNUM dsa_mod_inverse_fermat(const BIGNUM k, const BIGNUM *q,
415c3356 P	28	BN_CTX *ctx);
c0711f7f DSH	29
c0711f7f DSH	30	static DSA_METHOD openssl_dsa_meth = {
0f113f3e MC	31	"OpenSSL DSA method",
	32	dsa_do_sign,
	33	dsa_sign_setup_no_digest,
	34	dsa_do_verify,
	35	NULL, /* dsa_mod_exp, */
	36	NULL, /* dsa_bn_mod_exp, */
	37	dsa_init,
	38	dsa_finish,
	39	DSA_FLAG_FIPS_METHOD,
	40	NULL,
	41	NULL,
	42	NULL
c0711f7f DSH	43	};
c0711f7f DSH	44
076fc555 RS	45	static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
	46
	47	void DSA_set_default_method(const DSA_METHOD *meth)
	48	{
	49	default_DSA_method = meth;
	50	}
	51
	52	const DSA_METHOD *DSA_get_default_method(void)
	53	{
	54	return default_DSA_method;
	55	}
	56
a4aba800	57	const DSA_METHOD *DSA_OpenSSL(void)
c0711f7f	58	{
0f113f3e	59	return &openssl_dsa_meth;
c0711f7f DSH	60	}
	61
	62	static DSA_SIG dsa_do_sign(const unsigned char dgst, int dlen, DSA *dsa)
0f113f3e	63	{
706a13f1	64	BIGNUM *kinv = NULL;
7f9822a4	65	BIGNUM m, blind, blindm, tmp;
0f113f3e MC	66	BN_CTX *ctx = NULL;
	67	int reason = ERR_R_BN_LIB;
	68	DSA_SIG *ret = NULL;
706a13f1	69	int rv = 0;
0f113f3e	70
7f9822a4	71	if (dsa->p == NULL \|\| dsa->q == NULL \|\| dsa->g == NULL) {
0f113f3e MC	72	reason = DSA_R_MISSING_PARAMETERS;
	73	goto err;
	74	}
	75
706a13f1 DSH	76	ret = DSA_SIG_new();
706a13f1 DSH	77	if (ret == NULL)
0f113f3e	78	goto err;
8cc44d97 DSH	79	ret->r = BN_new();
	80	ret->s = BN_new();
	81	if (ret->r == NULL \|\| ret->s == NULL)
	82	goto err;
706a13f1	83
0f113f3e MC	84	ctx = BN_CTX_new();
	85	if (ctx == NULL)
	86	goto err;
7f9822a4 MC	87	m = BN_CTX_get(ctx);
	88	blind = BN_CTX_get(ctx);
	89	blindm = BN_CTX_get(ctx);
	90	tmp = BN_CTX_get(ctx);
	91	if (tmp == NULL)
	92	goto err;
	93
0f113f3e	94	redo:
9267c11b	95	if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
e1d9f1ab	96	goto err;
0f113f3e MC	97
	98	if (dlen > BN_num_bytes(dsa->q))
	99	/*
	100	* if the digest length is greater than the size of q use the
	101	* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
	102	* 4.2
	103	*/
	104	dlen = BN_num_bytes(dsa->q);
	105	if (BN_bin2bn(dgst, dlen, m) == NULL)
	106	goto err;
	107
7f9822a4 MC	108	/*
	109	* The normal signature calculation is:
	110	*
	111	* s := k^-1 * (m + r * priv_key) mod q
	112	*
	113	* We will blind this to protect against side channel attacks
	114	*
	115	* s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
	116	*/
	117
	118	/* Generate a blinding value */
	119	do {
	120	if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1,
	121	BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
0f113f3e	122	goto err;
7f9822a4 MC	123	} while (BN_is_zero(blind));
	124	BN_set_flags(blind, BN_FLG_CONSTTIME);
	125	BN_set_flags(blindm, BN_FLG_CONSTTIME);
	126	BN_set_flags(tmp, BN_FLG_CONSTTIME);
	127
	128	/* tmp := blind * priv_key * r mod q */
	129	if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx))
	130	goto err;
	131	if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx))
	132	goto err;
	133
	134	/* blindm := blind * m mod q */
	135	if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx))
	136	goto err;
	137
	138	/* s : = (blind * priv_key * r) + (blind * m) mod q */
	139	if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q))
	140	goto err;
	141
	142	/* s := s * k^-1 mod q */
9267c11b	143	if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
0f113f3e MC	144	goto err;
0f113f3e MC	145
7f9822a4 MC	146	/* s:= s * blind^-1 mod q */
	147	if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL)
	148	goto err;
	149	if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx))
	150	goto err;
	151
0f113f3e MC	152	/*
	153	* Redo if r or s is zero as required by FIPS 186-3: this is very
	154	* unlikely.
	155	*/
9267c11b	156	if (BN_is_zero(ret->r) \|\| BN_is_zero(ret->s))
0f113f3e	157	goto redo;
706a13f1 DSH	158
706a13f1 DSH	159	rv = 1;
0f113f3e MC	160
0f113f3e MC	161	err:
706a13f1	162	if (rv == 0) {
0f113f3e	163	DSAerr(DSA_F_DSA_DO_SIGN, reason);
706a13f1 DSH	164	DSA_SIG_free(ret);
706a13f1 DSH	165	ret = NULL;
0f113f3e	166	}
23a1d5e9	167	BN_CTX_free(ctx);
23a1d5e9	168	BN_clear_free(kinv);
706a13f1	169	return ret;
0f113f3e	170	}
c0711f7f	171
8d6a75dc	172	static int dsa_sign_setup_no_digest(DSA dsa, BN_CTX ctx_in,
0f113f3e MC	173	BIGNUM kinvp, BIGNUM rp)
	174	{
	175	return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
190c615d AL	176	}
190c615d AL	177
8d6a75dc	178	static int dsa_sign_setup(DSA dsa, BN_CTX ctx_in,
0f113f3e MC	179	BIGNUM kinvp, BIGNUM rp,
	180	const unsigned char *dgst, int dlen)
	181	{
	182	BN_CTX *ctx = NULL;
033dc8fa	183	BIGNUM k, kinv = NULL, r = rp;
a9cfb8c2	184	BIGNUM *l;
0f113f3e	185	int ret = 0;
a9cfb8c2	186	int q_bits, q_words;
0f113f3e MC	187
	188	if (!dsa->p \|\| !dsa->q \|\| !dsa->g) {
	189	DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
	190	return 0;
	191	}
	192
	193	k = BN_new();
c0caa945	194	l = BN_new();
a9cfb8c2	195	if (k == NULL \|\| l == NULL)
0f113f3e MC	196	goto err;
	197
	198	if (ctx_in == NULL) {
	199	if ((ctx = BN_CTX_new()) == NULL)
	200	goto err;
	201	} else
	202	ctx = ctx_in;
	203
c0caa945 P	204	/* Preallocate space */
c0caa945 P	205	q_bits = BN_num_bits(dsa->q);
a9cfb8c2 P	206	q_words = bn_get_top(dsa->q);
	207	if (!bn_wexpand(k, q_words + 2)
	208	\|\| !bn_wexpand(l, q_words + 2))
c0caa945 P	209	goto err;
c0caa945 P	210
0f113f3e MC	211	/* Get random k */
0f113f3e MC	212	do {
0f113f3e MC	213	if (dgst != NULL) {
	214	/*
	215	* We calculate k from SHA512(private_key + H(message) + random).
	216	* This protects the private key from a weak PRNG.
	217	*/
	218	if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
	219	dlen, ctx))
	220	goto err;
ddc6a5c8	221	} else if (!BN_priv_rand_range(k, dsa->q))
0f113f3e MC	222	goto err;
	223	} while (BN_is_zero(k));
	224
47ae05ba	225	BN_set_flags(k, BN_FLG_CONSTTIME);
00496b64	226	BN_set_flags(l, BN_FLG_CONSTTIME);
47ae05ba	227
0f113f3e MC	228	if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
0f113f3e MC	229	if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
d188a536	230	dsa->lock, dsa->p, ctx))
0f113f3e MC	231	goto err;
	232	}
	233
	234	/* Compute r = (g^k mod p) mod q */
	235
5584f65a MC	236	/*
5584f65a MC	237	* We do not want timing information to leak the length of k, so we
c0caa945 P	238	* compute G^k using an equivalent scalar of fixed bit-length.
	239	*
	240	* We unconditionally perform both of these additions to prevent a
	241	* small timing information leakage. We then choose the sum that is
	242	* one bit longer than the modulus.
	243	*
a9cfb8c2 P	244	* There are some concerns about the efficacy of doing this. More
	245	* specificly refer to the discussion starting with:
	246	* https://github.com/openssl/openssl/pull/7486#discussion_r228323705
	247	* The fix is to rework BN so these gymnastics aren't required.
5584f65a	248	*/
c0caa945	249	if (!BN_add(l, k, dsa->q)
a9cfb8c2	250	\|\| !BN_add(k, l, dsa->q))
5584f65a	251	goto err;
39994462	252
a9cfb8c2 P	253	BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);
a9cfb8c2 P	254
f943e640	255	if ((dsa)->meth->bn_mod_exp != NULL) {
033dc8fa	256	if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
f943e640 MC	257	dsa->method_mont_p))
	258	goto err;
	259	} else {
033dc8fa	260	if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
f943e640 MC	261	goto err;
	262	}
	263
0f113f3e MC	264	if (!BN_mod(r, r, dsa->q, ctx))
	265	goto err;
	266
a9cfb8c2	267	/* Compute part of 's = inv(k) (m + xr) mod q' */
415c3356	268	if ((kinv = dsa_mod_inverse_fermat(k, dsa->q, ctx)) == NULL)
0f113f3e MC	269	goto err;
0f113f3e MC	270
23a1d5e9	271	BN_clear_free(*kinvp);
0f113f3e MC	272	*kinvp = kinv;
0f113f3e MC	273	kinv = NULL;
0f113f3e MC	274	ret = 1;
0f113f3e MC	275	err:
706a13f1	276	if (!ret)
0f113f3e	277	DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
23a1d5e9	278	if (ctx != ctx_in)
0f113f3e MC	279	BN_CTX_free(ctx);
0f113f3e MC	280	BN_clear_free(k);
c0caa945	281	BN_clear_free(l);
706a13f1	282	return ret;
0f113f3e MC	283	}
	284
	285	static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
	286	DSA_SIG sig, DSA dsa)
	287	{
	288	BN_CTX *ctx;
	289	BIGNUM u1, u2, *t1;
	290	BN_MONT_CTX *mont = NULL;
9267c11b	291	const BIGNUM r, s;
0f113f3e MC	292	int ret = -1, i;
	293	if (!dsa->p \|\| !dsa->q \|\| !dsa->g) {
	294	DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
	295	return -1;
	296	}
	297
	298	i = BN_num_bits(dsa->q);
	299	/* fips 186-3 allows only different sizes for q */
	300	if (i != 160 && i != 224 && i != 256) {
	301	DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
	302	return -1;
	303	}
	304
	305	if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
	306	DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
	307	return -1;
	308	}
	309	u1 = BN_new();
	310	u2 = BN_new();
	311	t1 = BN_new();
	312	ctx = BN_CTX_new();
90945fa3	313	if (u1 == NULL \|\| u2 == NULL \|\| t1 == NULL \|\| ctx == NULL)
0f113f3e MC	314	goto err;
0f113f3e MC	315
9267c11b	316	DSA_SIG_get0(sig, &r, &s);
706a13f1 DSH	317
	318	if (BN_is_zero(r) \|\| BN_is_negative(r) \|\|
	319	BN_ucmp(r, dsa->q) >= 0) {
0f113f3e MC	320	ret = 0;
	321	goto err;
	322	}
706a13f1 DSH	323	if (BN_is_zero(s) \|\| BN_is_negative(s) \|\|
706a13f1 DSH	324	BN_ucmp(s, dsa->q) >= 0) {
0f113f3e MC	325	ret = 0;
	326	goto err;
	327	}
	328
	329	/*
	330	* Calculate W = inv(S) mod Q save W in u2
	331	*/
706a13f1	332	if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
0f113f3e MC	333	goto err;
	334
	335	/* save M in u1 */
	336	if (dgst_len > (i >> 3))
	337	/*
	338	* if the digest length is greater than the size of q use the
	339	* BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
	340	* 4.2
	341	*/
	342	dgst_len = (i >> 3);
	343	if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
	344	goto err;
	345
	346	/* u1 = M * w mod q */
	347	if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
	348	goto err;
	349
	350	/* u2 = r * w mod q */
706a13f1	351	if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
0f113f3e MC	352	goto err;
	353
	354	if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
	355	mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
d188a536	356	dsa->lock, dsa->p, ctx);
0f113f3e MC	357	if (!mont)
	358	goto err;
	359	}
	360
f943e640 MC	361	if (dsa->meth->dsa_mod_exp != NULL) {
	362	if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
	363	dsa->p, ctx, mont))
	364	goto err;
	365	} else {
	366	if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
	367	mont))
	368	goto err;
	369	}
	370
0f113f3e MC	371	/* let u1 = u1 mod q */
	372	if (!BN_mod(u1, t1, dsa->q, ctx))
	373	goto err;
	374
	375	/*
	376	* V is now in u1. If the signature is correct, it will be equal to R.
	377	*/
706a13f1	378	ret = (BN_ucmp(u1, r) == 0);
0f113f3e MC	379
	380	err:
	381	if (ret < 0)
	382	DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
23a1d5e9 RS	383	BN_CTX_free(ctx);
	384	BN_free(u1);
	385	BN_free(u2);
	386	BN_free(t1);
26a7d938	387	return ret;
0f113f3e	388	}
c0711f7f DSH	389
	390	static int dsa_init(DSA *dsa)
	391	{
0f113f3e	392	dsa->flags \|= DSA_FLAG_CACHE_MONT_P;
208fb891	393	return 1;
c0711f7f DSH	394	}
	395
	396	static int dsa_finish(DSA *dsa)
	397	{
23a1d5e9	398	BN_MONT_CTX_free(dsa->method_mont_p);
208fb891	399	return 1;
c0711f7f	400	}
415c3356 P	401
	402	/*
	403	* Compute the inverse of k modulo q.
	404	* Since q is prime, Fermat's Little Theorem applies, which reduces this to
	405	* mod-exp operation. Both the exponent and modulus are public information
	406	* so a mod-exp that doesn't leak the base is sufficient. A newly allocated
	407	* BIGNUM is returned which the caller must free.
	408	*/
	409	static BIGNUM dsa_mod_inverse_fermat(const BIGNUM k, const BIGNUM *q,
	410	BN_CTX *ctx)
	411	{
	412	BIGNUM *res = NULL;
	413	BIGNUM r, e;
	414
	415	if ((r = BN_new()) == NULL)
	416	return NULL;
	417
	418	BN_CTX_start(ctx);
	419	if ((e = BN_CTX_get(ctx)) != NULL
	420	&& BN_set_word(r, 2)
	421	&& BN_sub(e, q, r)
	422	&& BN_mod_exp_mont(r, k, e, q, ctx, NULL))
	423	res = r;
	424	else
	425	BN_free(r);
	426	BN_CTX_end(ctx);
	427	return res;
	428	}