-/* crypto/dsa/dsa_ossl.c */
-/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
- * All rights reserved.
+/*
+ * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
*
- * This package is an SSL implementation written
- * by Eric Young (eay@cryptsoft.com).
- * The implementation was written so as to conform with Netscapes SSL.
- *
- * This library is free for commercial and non-commercial use as long as
- * the following conditions are aheared to. The following conditions
- * apply to all code found in this distribution, be it the RC4, RSA,
- * lhash, DES, etc., code; not just the SSL code. The SSL documentation
- * included with this distribution is covered by the same copyright terms
- * except that the holder is Tim Hudson (tjh@cryptsoft.com).
- *
- * Copyright remains Eric Young's, and as such any Copyright notices in
- * the code are not to be removed.
- * If this package is used in a product, Eric Young should be given attribution
- * as the author of the parts of the library used.
- * This can be in the form of a textual message at program startup or
- * in documentation (online or textual) provided with the package.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the copyright
- * notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- * must display the following acknowledgement:
- * "This product includes cryptographic software written by
- * Eric Young (eay@cryptsoft.com)"
- * The word 'cryptographic' can be left out if the rouines from the library
- * being used are not cryptographic related :-).
- * 4. If you include any Windows specific code (or a derivative thereof) from
- * the apps directory (application code) you must include an acknowledgement:
- * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
- *
- * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- *
- * The licence and distribution terms for any publically available version or
- * derivative of this code cannot be changed. i.e. this code cannot simply be
- * copied and put under another distribution licence
- * [including the GNU Public Licence.]
+ * 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
*/
-/* Original version from Steven Schoch <schoch@sheba.arc.nasa.gov> */
-
#include <stdio.h>
#include "internal/cryptlib.h"
+#include "internal/bn_int.h"
#include <openssl/bn.h>
#include <openssl/sha.h>
-#include <openssl/dsa.h>
-#include <openssl/rand.h>
+#include "dsa_locl.h"
#include <openssl/asn1.h>
static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
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",
NULL
};
-/*-
- * These macro wrappers replace attempts to use the dsa_mod_exp() and
- * bn_mod_exp() handlers in the DSA_METHOD structure. We avoid the problem of
- * having a the macro work as an expression by bundling an "err_instr". So;
- *
- * if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx,
- * dsa->method_mont_p)) goto err;
- *
- * can be replaced by;
- *
- * DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, &k, dsa->p, ctx,
- * dsa->method_mont_p);
- */
+static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
-#define DSA_MOD_EXP(err_instr,dsa,rr,a1,p1,a2,p2,m,ctx,in_mont) \
- do { \
- int _tmp_res53; \
- if ((dsa)->meth->dsa_mod_exp) \
- _tmp_res53 = (dsa)->meth->dsa_mod_exp((dsa), (rr), (a1), (p1), \
- (a2), (p2), (m), (ctx), (in_mont)); \
- else \
- _tmp_res53 = BN_mod_exp2_mont((rr), (a1), (p1), (a2), (p2), \
- (m), (ctx), (in_mont)); \
- if (!_tmp_res53) err_instr; \
- } while(0)
-#define DSA_BN_MOD_EXP(err_instr,dsa,r,a,p,m,ctx,m_ctx) \
- do { \
- int _tmp_res53; \
- if ((dsa)->meth->bn_mod_exp) \
- _tmp_res53 = (dsa)->meth->bn_mod_exp((dsa), (r), (a), (p), \
- (m), (ctx), (m_ctx)); \
- else \
- _tmp_res53 = BN_mod_exp_mont((r), (a), (p), (m), (ctx), (m_ctx)); \
- if (!_tmp_res53) err_instr; \
- } while(0)
+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)
{
static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
{
- BIGNUM *kinv = NULL, *r = NULL, *s = NULL;
- BIGNUM *m;
- BIGNUM *xr;
+ BIGNUM *kinv = NULL;
+ BIGNUM *m, *blind, *blindm, *tmp;
BN_CTX *ctx = NULL;
int reason = ERR_R_BN_LIB;
DSA_SIG *ret = NULL;
- int noredo = 0;
+ int rv = 0;
- m = BN_new();
- xr = BN_new();
- if (!m || !xr)
- goto err;
-
- if (!dsa->p || !dsa->q || !dsa->g) {
+ if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) {
reason = DSA_R_MISSING_PARAMETERS;
goto err;
}
- s = BN_new();
- if (s == NULL)
+ 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->kinv == NULL) || (dsa->r == NULL)) {
- if (!dsa_sign_setup(dsa, ctx, &kinv, &r, dgst, dlen))
- goto err;
- } else {
- kinv = dsa->kinv;
- dsa->kinv = NULL;
- r = dsa->r;
- dsa->r = NULL;
- noredo = 1;
- }
+ if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
+ goto err;
if (dlen > BN_num_bytes(dsa->q))
/*
if (BN_bin2bn(dgst, dlen, m) == NULL)
goto err;
- /* Compute s = inv(k) (m + xr) mod q */
- if (!BN_mod_mul(xr, dsa->priv_key, r, dsa->q, ctx))
- goto err; /* s = xr */
- if (!BN_add(s, xr, m))
- goto err; /* s = m + xr */
- if (BN_cmp(s, dsa->q) > 0)
- if (!BN_sub(s, s, dsa->q))
+ /*
+ * 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;
- if (!BN_mod_mul(s, s, kinv, dsa->q, ctx))
+ } 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;
- ret = DSA_SIG_new();
- if (ret == NULL)
+ /* 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(r) || BN_is_zero(s)) {
- if (noredo) {
- reason = DSA_R_NEED_NEW_SETUP_VALUES;
- goto err;
- }
+ if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
goto redo;
- }
- ret->r = r;
- ret->s = s;
+
+ rv = 1;
err:
- if (!ret) {
+ if (rv == 0) {
DSAerr(DSA_F_DSA_DO_SIGN, reason);
- BN_free(r);
- BN_free(s);
+ DSA_SIG_free(ret);
+ ret = NULL;
}
BN_CTX_free(ctx);
- BN_clear_free(m);
- BN_clear_free(xr);
BN_clear_free(kinv);
- return (ret);
+ return ret;
}
static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
const unsigned char *dgst, int dlen)
{
BN_CTX *ctx = NULL;
- BIGNUM *k, *kq, *K, *kinv = NULL, *r = 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);
}
k = BN_new();
- kq = BN_new();
- if (!k || !kq)
+ l = BN_new();
+ if (k == NULL || l == NULL)
goto err;
if (ctx_in == NULL) {
} else
ctx = ctx_in;
- if ((r = BN_new()) == NULL)
+ /* 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 */
if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
dlen, ctx))
goto err;
- } else if (!BN_rand_range(k, dsa->q))
+ } else if (!BN_priv_rand_range(k, dsa->q))
goto err;
} while (BN_is_zero(k));
- if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
- BN_set_flags(k, BN_FLG_CONSTTIME);
- }
+ 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,
- CRYPTO_LOCK_DSA, dsa->p, ctx))
+ dsa->lock, dsa->p, ctx))
goto err;
}
/* Compute r = (g^k mod p) mod q */
- if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {
- if (!BN_copy(kq, k))
- goto err;
+ /*
+ * 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;
- /*
- * We do not want timing information to leak the length of k, so we
- * compute g^k using an equivalent exponent of fixed length. (This
- * is a kludge that we need because the BN_mod_exp_mont() does not
- * let us specify the desired timing behaviour.)
- */
+ BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);
- if (!BN_add(kq, kq, dsa->q))
- goto err;
- if (BN_num_bits(kq) <= BN_num_bits(dsa->q)) {
- if (!BN_add(kq, kq, dsa->q))
+ 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;
- }
-
- K = kq;
} else {
- K = k;
+ if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
+ goto err;
}
- DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx,
- dsa->method_mont_p);
+
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)
+ /* 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;
- BN_clear_free(*rp);
- *rp = r;
ret = 1;
err:
- if (!ret) {
+ if (!ret)
DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
- BN_clear_free(r);
- }
if (ctx != ctx_in)
BN_CTX_free(ctx);
BN_clear_free(k);
- BN_clear_free(kq);
- return (ret);
+ BN_clear_free(l);
+ return ret;
}
static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
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);
u2 = BN_new();
t1 = BN_new();
ctx = BN_CTX_new();
- if (!u1 || !u2 || !t1 || !ctx)
+ if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
goto err;
- if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||
- BN_ucmp(sig->r, dsa->q) >= 0) {
+ 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(sig->s) || BN_is_negative(sig->s) ||
- BN_ucmp(sig->s, dsa->q) >= 0) {
+ 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, sig->s, dsa->q, ctx)) == NULL)
+ if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
goto err;
/* save M in u1 */
goto err;
/* u2 = r * w mod q */
- if (!BN_mod_mul(u2, sig->r, u2, dsa->q, ctx))
+ 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,
- CRYPTO_LOCK_DSA, dsa->p, ctx);
+ dsa->lock, dsa->p, ctx);
if (!mont)
goto err;
}
- DSA_MOD_EXP(goto err, dsa, t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
- mont);
- /* BN_copy(&u1,&t1); */
+ 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, sig->r) == 0);
+ ret = (BN_ucmp(u1, r) == 0);
err:
if (ret < 0)
BN_free(u1);
BN_free(u2);
BN_free(t1);
- return (ret);
+ return ret;
}
static int dsa_init(DSA *dsa)
{
dsa->flags |= DSA_FLAG_CACHE_MONT_P;
- return (1);
+ return 1;
}
static int dsa_finish(DSA *dsa)
{
BN_MONT_CTX_free(dsa->method_mont_p);
- return (1);
+ 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;
}
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