2 * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
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
11 #include "internal/cryptlib.h"
12 #include "crypto/bn.h"
13 #include <openssl/bn.h>
14 #include <openssl/sha.h>
15 #include "dsa_local.h"
16 #include <openssl/asn1.h>
18 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
19 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
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);
25 static int dsa_init(DSA *dsa);
26 static int dsa_finish(DSA *dsa);
27 static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
30 static DSA_METHOD openssl_dsa_meth = {
33 dsa_sign_setup_no_digest,
35 NULL, /* dsa_mod_exp, */
36 NULL, /* dsa_bn_mod_exp, */
45 static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
48 void DSA_set_default_method(const DSA_METHOD *meth)
50 default_DSA_method = meth;
52 #endif /* FIPS_MODE */
54 const DSA_METHOD *DSA_get_default_method(void)
56 return default_DSA_method;
59 const DSA_METHOD *DSA_OpenSSL(void)
61 return &openssl_dsa_meth;
64 DSA_SIG *dsa_do_sign_int(OPENSSL_CTX *libctx, const unsigned char *dgst,
68 BIGNUM *m, *blind, *blindm, *tmp;
70 int reason = ERR_R_BN_LIB;
74 if (dsa->params.p == NULL
75 || dsa->params.q == NULL
76 || dsa->params.g == NULL) {
77 reason = DSA_R_MISSING_PARAMETERS;
80 if (dsa->priv_key == NULL) {
81 reason = DSA_R_MISSING_PRIVATE_KEY;
90 if (ret->r == NULL || ret->s == NULL)
93 ctx = BN_CTX_new_ex(libctx);
97 blind = BN_CTX_get(ctx);
98 blindm = BN_CTX_get(ctx);
99 tmp = BN_CTX_get(ctx);
104 if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
107 if (dlen > BN_num_bytes(dsa->params.q))
109 * if the digest length is greater than the size of q use the
110 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
113 dlen = BN_num_bytes(dsa->params.q);
114 if (BN_bin2bn(dgst, dlen, m) == NULL)
118 * The normal signature calculation is:
120 * s := k^-1 * (m + r * priv_key) mod q
122 * We will blind this to protect against side channel attacks
124 * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
127 /* Generate a blinding value */
129 if (!BN_priv_rand_ex(blind, BN_num_bits(dsa->params.q) - 1,
130 BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, ctx))
132 } while (BN_is_zero(blind));
133 BN_set_flags(blind, BN_FLG_CONSTTIME);
134 BN_set_flags(blindm, BN_FLG_CONSTTIME);
135 BN_set_flags(tmp, BN_FLG_CONSTTIME);
137 /* tmp := blind * priv_key * r mod q */
138 if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->params.q, ctx))
140 if (!BN_mod_mul(tmp, tmp, ret->r, dsa->params.q, ctx))
143 /* blindm := blind * m mod q */
144 if (!BN_mod_mul(blindm, blind, m, dsa->params.q, ctx))
147 /* s : = (blind * priv_key * r) + (blind * m) mod q */
148 if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->params.q))
151 /* s := s * k^-1 mod q */
152 if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->params.q, ctx))
155 /* s:= s * blind^-1 mod q */
156 if (BN_mod_inverse(blind, blind, dsa->params.q, ctx) == NULL)
158 if (!BN_mod_mul(ret->s, ret->s, blind, dsa->params.q, ctx))
162 * Redo if r or s is zero as required by FIPS 186-3: this is very
165 if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
181 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
183 return dsa_do_sign_int(NULL, dgst, dlen, dsa);
186 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
187 BIGNUM **kinvp, BIGNUM **rp)
189 return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
192 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
193 BIGNUM **kinvp, BIGNUM **rp,
194 const unsigned char *dgst, int dlen)
197 BIGNUM *k, *kinv = NULL, *r = *rp;
202 if (!dsa->params.p || !dsa->params.q || !dsa->params.g) {
203 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
207 /* Reject obviously invalid parameters */
208 if (BN_is_zero(dsa->params.p)
209 || BN_is_zero(dsa->params.q)
210 || BN_is_zero(dsa->params.g)) {
211 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_INVALID_PARAMETERS);
214 if (dsa->priv_key == NULL) {
215 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PRIVATE_KEY);
221 if (k == NULL || l == NULL)
224 if (ctx_in == NULL) {
225 /* if you don't pass in ctx_in you get a default libctx */
226 if ((ctx = BN_CTX_new_ex(NULL)) == NULL)
231 /* Preallocate space */
232 q_bits = BN_num_bits(dsa->params.q);
233 q_words = bn_get_top(dsa->params.q);
234 if (!bn_wexpand(k, q_words + 2)
235 || !bn_wexpand(l, q_words + 2))
242 * We calculate k from SHA512(private_key + H(message) + random).
243 * This protects the private key from a weak PRNG.
245 if (!BN_generate_dsa_nonce(k, dsa->params.q, dsa->priv_key, dgst,
248 } else if (!BN_priv_rand_range_ex(k, dsa->params.q, ctx))
250 } while (BN_is_zero(k));
252 BN_set_flags(k, BN_FLG_CONSTTIME);
253 BN_set_flags(l, BN_FLG_CONSTTIME);
255 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
256 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
257 dsa->lock, dsa->params.p, ctx))
261 /* Compute r = (g^k mod p) mod q */
264 * We do not want timing information to leak the length of k, so we
265 * compute G^k using an equivalent scalar of fixed bit-length.
267 * We unconditionally perform both of these additions to prevent a
268 * small timing information leakage. We then choose the sum that is
269 * one bit longer than the modulus.
271 * There are some concerns about the efficacy of doing this. More
272 * specifically refer to the discussion starting with:
273 * https://github.com/openssl/openssl/pull/7486#discussion_r228323705
274 * The fix is to rework BN so these gymnastics aren't required.
276 if (!BN_add(l, k, dsa->params.q)
277 || !BN_add(k, l, dsa->params.q))
280 BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);
282 if ((dsa)->meth->bn_mod_exp != NULL) {
283 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->params.g, k, dsa->params.p,
284 ctx, dsa->method_mont_p))
287 if (!BN_mod_exp_mont(r, dsa->params.g, k, dsa->params.p, ctx,
292 if (!BN_mod(r, r, dsa->params.q, ctx))
295 /* Compute part of 's = inv(k) (m + xr) mod q' */
296 if ((kinv = dsa_mod_inverse_fermat(k, dsa->params.q, ctx)) == NULL)
299 BN_clear_free(*kinvp);
305 DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
313 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
314 DSA_SIG *sig, DSA *dsa)
317 BIGNUM *u1, *u2, *t1;
318 BN_MONT_CTX *mont = NULL;
321 if (dsa->params.p == NULL
322 || dsa->params.q == NULL
323 || dsa->params.g == NULL) {
324 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
328 i = BN_num_bits(dsa->params.q);
329 /* fips 186-3 allows only different sizes for q */
330 if (i != 160 && i != 224 && i != 256) {
331 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
335 if (BN_num_bits(dsa->params.p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
336 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
342 ctx = BN_CTX_new_ex(NULL); /* verify does not need a libctx */
343 if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
346 DSA_SIG_get0(sig, &r, &s);
348 if (BN_is_zero(r) || BN_is_negative(r) ||
349 BN_ucmp(r, dsa->params.q) >= 0) {
353 if (BN_is_zero(s) || BN_is_negative(s) ||
354 BN_ucmp(s, dsa->params.q) >= 0) {
360 * Calculate W = inv(S) mod Q save W in u2
362 if ((BN_mod_inverse(u2, s, dsa->params.q, ctx)) == NULL)
366 if (dgst_len > (i >> 3))
368 * if the digest length is greater than the size of q use the
369 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
373 if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
376 /* u1 = M * w mod q */
377 if (!BN_mod_mul(u1, u1, u2, dsa->params.q, ctx))
380 /* u2 = r * w mod q */
381 if (!BN_mod_mul(u2, r, u2, dsa->params.q, ctx))
384 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
385 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
386 dsa->lock, dsa->params.p, ctx);
391 if (dsa->meth->dsa_mod_exp != NULL) {
392 if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->params.g, u1, dsa->pub_key, u2,
393 dsa->params.p, ctx, mont))
396 if (!BN_mod_exp2_mont(t1, dsa->params.g, u1, dsa->pub_key, u2,
397 dsa->params.p, ctx, mont))
401 /* let u1 = u1 mod q */
402 if (!BN_mod(u1, t1, dsa->params.q, ctx))
406 * V is now in u1. If the signature is correct, it will be equal to R.
408 ret = (BN_ucmp(u1, r) == 0);
412 DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
420 static int dsa_init(DSA *dsa)
422 dsa->flags |= DSA_FLAG_CACHE_MONT_P;
423 ffc_params_init(&dsa->params);
427 static int dsa_finish(DSA *dsa)
429 BN_MONT_CTX_free(dsa->method_mont_p);
434 * Compute the inverse of k modulo q.
435 * Since q is prime, Fermat's Little Theorem applies, which reduces this to
436 * mod-exp operation. Both the exponent and modulus are public information
437 * so a mod-exp that doesn't leak the base is sufficient. A newly allocated
438 * BIGNUM is returned which the caller must free.
440 static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
446 if ((r = BN_new()) == NULL)
450 if ((e = BN_CTX_get(ctx)) != NULL
453 && BN_mod_exp_mont(r, k, e, q, ctx, NULL))