2 * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
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
11 #include "internal/cryptlib.h"
12 #include <openssl/bn.h>
13 #include <openssl/sha.h>
15 #include <openssl/asn1.h>
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,
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);
27 static DSA_METHOD openssl_dsa_meth = {
30 dsa_sign_setup_no_digest,
32 NULL, /* dsa_mod_exp, */
33 NULL, /* dsa_bn_mod_exp, */
42 static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
44 void DSA_set_default_method(const DSA_METHOD *meth)
46 default_DSA_method = meth;
49 const DSA_METHOD *DSA_get_default_method(void)
51 return default_DSA_method;
54 const DSA_METHOD *DSA_OpenSSL(void)
56 return &openssl_dsa_meth;
59 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
62 BIGNUM *m, *blind, *blindm, *tmp;
64 int reason = ERR_R_BN_LIB;
68 if (dsa->p == NULL || dsa->q == NULL || dsa->g == NULL) {
69 reason = DSA_R_MISSING_PARAMETERS;
78 if (ret->r == NULL || ret->s == NULL)
85 blind = BN_CTX_get(ctx);
86 blindm = BN_CTX_get(ctx);
87 tmp = BN_CTX_get(ctx);
92 if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
95 if (dlen > BN_num_bytes(dsa->q))
97 * if the digest length is greater than the size of q use the
98 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
101 dlen = BN_num_bytes(dsa->q);
102 if (BN_bin2bn(dgst, dlen, m) == NULL)
106 * The normal signature calculation is:
108 * s := k^-1 * (m + r * priv_key) mod q
110 * We will blind this to protect against side channel attacks
112 * s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
115 /* Generate a blinding value */
117 if (!BN_priv_rand(blind, BN_num_bits(dsa->q) - 1,
118 BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY))
120 } while (BN_is_zero(blind));
121 BN_set_flags(blind, BN_FLG_CONSTTIME);
122 BN_set_flags(blindm, BN_FLG_CONSTTIME);
123 BN_set_flags(tmp, BN_FLG_CONSTTIME);
125 /* tmp := blind * priv_key * r mod q */
126 if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->q, ctx))
128 if (!BN_mod_mul(tmp, tmp, ret->r, dsa->q, ctx))
131 /* blindm := blind * m mod q */
132 if (!BN_mod_mul(blindm, blind, m, dsa->q, ctx))
135 /* s : = (blind * priv_key * r) + (blind * m) mod q */
136 if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->q))
139 /* s := s * k^-1 mod q */
140 if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->q, ctx))
143 /* s:= s * blind^-1 mod q */
144 if (BN_mod_inverse(blind, blind, dsa->q, ctx) == NULL)
146 if (!BN_mod_mul(ret->s, ret->s, blind, dsa->q, ctx))
150 * Redo if r or s is zero as required by FIPS 186-3: this is very
153 if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
160 DSAerr(DSA_F_DSA_DO_SIGN, reason);
169 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
170 BIGNUM **kinvp, BIGNUM **rp)
172 return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
175 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
176 BIGNUM **kinvp, BIGNUM **rp,
177 const unsigned char *dgst, int dlen)
180 BIGNUM *k, *kinv = NULL, *r = *rp;
185 if (!dsa->p || !dsa->q || !dsa->g) {
186 DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
193 if (k == NULL || l == NULL || m == NULL)
196 if (ctx_in == NULL) {
197 if ((ctx = BN_CTX_new()) == NULL)
202 /* Preallocate space */
203 q_bits = BN_num_bits(dsa->q);
204 if (!BN_set_bit(k, q_bits)
205 || !BN_set_bit(l, q_bits)
206 || !BN_set_bit(m, q_bits))
213 * We calculate k from SHA512(private_key + H(message) + random).
214 * This protects the private key from a weak PRNG.
216 if (!BN_generate_dsa_nonce(k, dsa->q, dsa->priv_key, dgst,
219 } else if (!BN_priv_rand_range(k, dsa->q))
221 } while (BN_is_zero(k));
223 BN_set_flags(k, BN_FLG_CONSTTIME);
225 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
226 if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
227 dsa->lock, dsa->p, ctx))
231 /* Compute r = (g^k mod p) mod q */
234 * We do not want timing information to leak the length of k, so we
235 * compute G^k using an equivalent scalar of fixed bit-length.
237 * We unconditionally perform both of these additions to prevent a
238 * small timing information leakage. We then choose the sum that is
239 * one bit longer than the modulus.
241 * TODO: revisit the BN_copy aiming for a memory access agnostic
244 if (!BN_add(l, k, dsa->q)
245 || !BN_add(m, l, dsa->q)
246 || !BN_copy(k, BN_num_bits(l) > q_bits ? l : m))
249 if ((dsa)->meth->bn_mod_exp != NULL) {
250 if (!dsa->meth->bn_mod_exp(dsa, r, dsa->g, k, dsa->p, ctx,
254 if (!BN_mod_exp_mont(r, dsa->g, k, dsa->p, ctx, dsa->method_mont_p))
258 if (!BN_mod(r, r, dsa->q, ctx))
261 /* Compute part of 's = inv(k) (m + xr) mod q' */
262 if ((kinv = BN_mod_inverse(NULL, k, dsa->q, ctx)) == NULL)
265 BN_clear_free(*kinvp);
271 DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
280 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
281 DSA_SIG *sig, DSA *dsa)
284 BIGNUM *u1, *u2, *t1;
285 BN_MONT_CTX *mont = NULL;
288 if (!dsa->p || !dsa->q || !dsa->g) {
289 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
293 i = BN_num_bits(dsa->q);
294 /* fips 186-3 allows only different sizes for q */
295 if (i != 160 && i != 224 && i != 256) {
296 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
300 if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
301 DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
308 if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
311 DSA_SIG_get0(sig, &r, &s);
313 if (BN_is_zero(r) || BN_is_negative(r) ||
314 BN_ucmp(r, dsa->q) >= 0) {
318 if (BN_is_zero(s) || BN_is_negative(s) ||
319 BN_ucmp(s, dsa->q) >= 0) {
325 * Calculate W = inv(S) mod Q save W in u2
327 if ((BN_mod_inverse(u2, s, dsa->q, ctx)) == NULL)
331 if (dgst_len > (i >> 3))
333 * if the digest length is greater than the size of q use the
334 * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
338 if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
341 /* u1 = M * w mod q */
342 if (!BN_mod_mul(u1, u1, u2, dsa->q, ctx))
345 /* u2 = r * w mod q */
346 if (!BN_mod_mul(u2, r, u2, dsa->q, ctx))
349 if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
350 mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
351 dsa->lock, dsa->p, ctx);
356 if (dsa->meth->dsa_mod_exp != NULL) {
357 if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->g, u1, dsa->pub_key, u2,
361 if (!BN_mod_exp2_mont(t1, dsa->g, u1, dsa->pub_key, u2, dsa->p, ctx,
366 /* let u1 = u1 mod q */
367 if (!BN_mod(u1, t1, dsa->q, ctx))
371 * V is now in u1. If the signature is correct, it will be equal to R.
373 ret = (BN_ucmp(u1, r) == 0);
377 DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
385 static int dsa_init(DSA *dsa)
387 dsa->flags |= DSA_FLAG_CACHE_MONT_P;
391 static int dsa_finish(DSA *dsa)
393 BN_MONT_CTX_free(dsa->method_mont_p);