crypto/dsa/dsa_ossl.c

   1 /*
   2  * Copyright 1995-2020 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 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);
  25 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
  26                                     BIGNUM **rp);
  27 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,
  28                           BIGNUM **rp, const unsigned char *dgst, int dlen);
  29 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
  30                          DSA_SIG *sig, DSA *dsa);
  31 static int dsa_init(DSA *dsa);
  32 static int dsa_finish(DSA *dsa);
  33 static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
  34                                       BN_CTX *ctx);
  35
  36 static DSA_METHOD openssl_dsa_meth = {
  37     "OpenSSL DSA method",
  38     dsa_do_sign,
  39     dsa_sign_setup_no_digest,
  40     dsa_do_verify,
  41     NULL,                       /* dsa_mod_exp, */
  42     NULL,                       /* dsa_bn_mod_exp, */
  43     dsa_init,
  44     dsa_finish,
  45     DSA_FLAG_FIPS_METHOD,
  46     NULL,
  47     NULL,
  48     NULL
  49 };
  50
  51 static const DSA_METHOD *default_DSA_method = &openssl_dsa_meth;
  52
  53 #ifndef FIPS_MODE
  54 void DSA_set_default_method(const DSA_METHOD *meth)
  55 {
  56     default_DSA_method = meth;
  57 }
  58 #endif /* FIPS_MODE */
  59
  60 const DSA_METHOD *DSA_get_default_method(void)
  61 {
  62     return default_DSA_method;
  63 }
  64
  65 const DSA_METHOD *DSA_OpenSSL(void)
  66 {
  67     return &openssl_dsa_meth;
  68 }
  69
  70 DSA_SIG *dsa_do_sign_int(const unsigned char *dgst, int dlen, DSA *dsa)
  71 {
  72     BIGNUM *kinv = NULL;
  73     BIGNUM *m, *blind, *blindm, *tmp;
  74     BN_CTX *ctx = NULL;
  75     int reason = ERR_R_BN_LIB;
  76     DSA_SIG *ret = NULL;
  77     int rv = 0;
  78
  79     if (dsa->params.p == NULL
  80         || dsa->params.q == NULL
  81         || dsa->params.g == NULL) {
  82         reason = DSA_R_MISSING_PARAMETERS;
  83         goto err;
  84     }
  85     if (dsa->priv_key == NULL) {
  86         reason = DSA_R_MISSING_PRIVATE_KEY;
  87         goto err;
  88     }
  89
  90     ret = DSA_SIG_new();
  91     if (ret == NULL)
  92         goto err;
  93     ret->r = BN_new();
  94     ret->s = BN_new();
  95     if (ret->r == NULL || ret->s == NULL)
  96         goto err;
  97
  98     ctx = BN_CTX_new_ex(dsa->libctx);
  99     if (ctx == NULL)
 100         goto err;
 101     m = BN_CTX_get(ctx);
 102     blind = BN_CTX_get(ctx);
 103     blindm = BN_CTX_get(ctx);
 104     tmp = BN_CTX_get(ctx);
 105     if (tmp == NULL)
 106         goto err;
 107
 108  redo:
 109     if (!dsa_sign_setup(dsa, ctx, &kinv, &ret->r, dgst, dlen))
 110         goto err;
 111
 112     if (dlen > BN_num_bytes(dsa->params.q))
 113         /*
 114          * if the digest length is greater than the size of q use the
 115          * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
 116          * 4.2
 117          */
 118         dlen = BN_num_bytes(dsa->params.q);
 119     if (BN_bin2bn(dgst, dlen, m) == NULL)
 120         goto err;
 121
 122     /*
 123      * The normal signature calculation is:
 124      *
 125      *   s := k^-1 * (m + r * priv_key) mod q
 126      *
 127      * We will blind this to protect against side channel attacks
 128      *
 129      *   s := blind^-1 * k^-1 * (blind * m + blind * r * priv_key) mod q
 130      */
 131
 132     /* Generate a blinding value */
 133     do {
 134         if (!BN_priv_rand_ex(blind, BN_num_bits(dsa->params.q) - 1,
 135                              BN_RAND_TOP_ANY, BN_RAND_BOTTOM_ANY, ctx))
 136             goto err;
 137     } while (BN_is_zero(blind));
 138     BN_set_flags(blind, BN_FLG_CONSTTIME);
 139     BN_set_flags(blindm, BN_FLG_CONSTTIME);
 140     BN_set_flags(tmp, BN_FLG_CONSTTIME);
 141
 142     /* tmp := blind * priv_key * r mod q */
 143     if (!BN_mod_mul(tmp, blind, dsa->priv_key, dsa->params.q, ctx))
 144         goto err;
 145     if (!BN_mod_mul(tmp, tmp, ret->r, dsa->params.q, ctx))
 146         goto err;
 147
 148     /* blindm := blind * m mod q */
 149     if (!BN_mod_mul(blindm, blind, m, dsa->params.q, ctx))
 150         goto err;
 151
 152     /* s : = (blind * priv_key * r) + (blind * m) mod q */
 153     if (!BN_mod_add_quick(ret->s, tmp, blindm, dsa->params.q))
 154         goto err;
 155
 156     /* s := s * k^-1 mod q */
 157     if (!BN_mod_mul(ret->s, ret->s, kinv, dsa->params.q, ctx))
 158         goto err;
 159
 160     /* s:= s * blind^-1 mod q */
 161     if (BN_mod_inverse(blind, blind, dsa->params.q, ctx) == NULL)
 162         goto err;
 163     if (!BN_mod_mul(ret->s, ret->s, blind, dsa->params.q, ctx))
 164         goto err;
 165
 166     /*
 167      * Redo if r or s is zero as required by FIPS 186-3: this is very
 168      * unlikely.
 169      */
 170     if (BN_is_zero(ret->r) || BN_is_zero(ret->s))
 171         goto redo;
 172
 173     rv = 1;
 174
 175  err:
 176     if (rv == 0) {
 177         DSAerr(0, reason);
 178         DSA_SIG_free(ret);
 179         ret = NULL;
 180     }
 181     BN_CTX_free(ctx);
 182     BN_clear_free(kinv);
 183     return ret;
 184 }
 185
 186 static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
 187 {
 188     return dsa_do_sign_int(dgst, dlen, dsa);
 189 }
 190
 191 static int dsa_sign_setup_no_digest(DSA *dsa, BN_CTX *ctx_in,
 192                                     BIGNUM **kinvp, BIGNUM **rp)
 193 {
 194     return dsa_sign_setup(dsa, ctx_in, kinvp, rp, NULL, 0);
 195 }
 196
 197 static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in,
 198                           BIGNUM **kinvp, BIGNUM **rp,
 199                           const unsigned char *dgst, int dlen)
 200 {
 201     BN_CTX *ctx = NULL;
 202     BIGNUM *k, *kinv = NULL, *r = *rp;
 203     BIGNUM *l;
 204     int ret = 0;
 205     int q_bits, q_words;
 206
 207     if (!dsa->params.p || !dsa->params.q || !dsa->params.g) {
 208         DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);
 209         return 0;
 210     }
 211
 212     /* Reject obviously invalid parameters */
 213     if (BN_is_zero(dsa->params.p)
 214         || BN_is_zero(dsa->params.q)
 215         || BN_is_zero(dsa->params.g)) {
 216         DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_INVALID_PARAMETERS);
 217         return 0;
 218     }
 219     if (dsa->priv_key == NULL) {
 220         DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PRIVATE_KEY);
 221         return 0;
 222     }
 223
 224     k = BN_new();
 225     l = BN_new();
 226     if (k == NULL || l == NULL)
 227         goto err;
 228
 229     if (ctx_in == NULL) {
 230         /* if you don't pass in ctx_in you get a default libctx */
 231         if ((ctx = BN_CTX_new_ex(NULL)) == NULL)
 232             goto err;
 233     } else
 234         ctx = ctx_in;
 235
 236     /* Preallocate space */
 237     q_bits = BN_num_bits(dsa->params.q);
 238     q_words = bn_get_top(dsa->params.q);
 239     if (!bn_wexpand(k, q_words + 2)
 240         || !bn_wexpand(l, q_words + 2))
 241         goto err;
 242
 243     /* Get random k */
 244     do {
 245         if (dgst != NULL) {
 246             /*
 247              * We calculate k from SHA512(private_key + H(message) + random).
 248              * This protects the private key from a weak PRNG.
 249              */
 250             if (!BN_generate_dsa_nonce(k, dsa->params.q, dsa->priv_key, dgst,
 251                                        dlen, ctx))
 252                 goto err;
 253         } else if (!BN_priv_rand_range_ex(k, dsa->params.q, ctx))
 254             goto err;
 255     } while (BN_is_zero(k));
 256
 257     BN_set_flags(k, BN_FLG_CONSTTIME);
 258     BN_set_flags(l, BN_FLG_CONSTTIME);
 259
 260     if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
 261         if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,
 262                                     dsa->lock, dsa->params.p, ctx))
 263             goto err;
 264     }
 265
 266     /* Compute r = (g^k mod p) mod q */
 267
 268     /*
 269      * We do not want timing information to leak the length of k, so we
 270      * compute G^k using an equivalent scalar of fixed bit-length.
 271      *
 272      * We unconditionally perform both of these additions to prevent a
 273      * small timing information leakage.  We then choose the sum that is
 274      * one bit longer than the modulus.
 275      *
 276      * There are some concerns about the efficacy of doing this.  More
 277      * specifically refer to the discussion starting with:
 278      *     https://github.com/openssl/openssl/pull/7486#discussion_r228323705
 279      * The fix is to rework BN so these gymnastics aren't required.
 280      */
 281     if (!BN_add(l, k, dsa->params.q)
 282         || !BN_add(k, l, dsa->params.q))
 283         goto err;
 284
 285     BN_consttime_swap(BN_is_bit_set(l, q_bits), k, l, q_words + 2);
 286
 287     if ((dsa)->meth->bn_mod_exp != NULL) {
 288             if (!dsa->meth->bn_mod_exp(dsa, r, dsa->params.g, k, dsa->params.p,
 289                                        ctx, dsa->method_mont_p))
 290                 goto err;
 291     } else {
 292             if (!BN_mod_exp_mont(r, dsa->params.g, k, dsa->params.p, ctx,
 293                                  dsa->method_mont_p))
 294                 goto err;
 295     }
 296
 297     if (!BN_mod(r, r, dsa->params.q, ctx))
 298         goto err;
 299
 300     /* Compute part of 's = inv(k) (m + xr) mod q' */
 301     if ((kinv = dsa_mod_inverse_fermat(k, dsa->params.q, ctx)) == NULL)
 302         goto err;
 303
 304     BN_clear_free(*kinvp);
 305     *kinvp = kinv;
 306     kinv = NULL;
 307     ret = 1;
 308  err:
 309     if (!ret)
 310         DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);
 311     if (ctx != ctx_in)
 312         BN_CTX_free(ctx);
 313     BN_clear_free(k);
 314     BN_clear_free(l);
 315     return ret;
 316 }
 317
 318 static int dsa_do_verify(const unsigned char *dgst, int dgst_len,
 319                          DSA_SIG *sig, DSA *dsa)
 320 {
 321     BN_CTX *ctx;
 322     BIGNUM *u1, *u2, *t1;
 323     BN_MONT_CTX *mont = NULL;
 324     const BIGNUM *r, *s;
 325     int ret = -1, i;
 326
 327     if (dsa->params.p == NULL
 328         || dsa->params.q == NULL
 329         || dsa->params.g == NULL) {
 330         DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);
 331         return -1;
 332     }
 333
 334     i = BN_num_bits(dsa->params.q);
 335     /* fips 186-3 allows only different sizes for q */
 336     if (i != 160 && i != 224 && i != 256) {
 337         DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);
 338         return -1;
 339     }
 340
 341     if (BN_num_bits(dsa->params.p) > OPENSSL_DSA_MAX_MODULUS_BITS) {
 342         DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);
 343         return -1;
 344     }
 345     u1 = BN_new();
 346     u2 = BN_new();
 347     t1 = BN_new();
 348     ctx = BN_CTX_new_ex(NULL); /* verify does not need a libctx */
 349     if (u1 == NULL || u2 == NULL || t1 == NULL || ctx == NULL)
 350         goto err;
 351
 352     DSA_SIG_get0(sig, &r, &s);
 353
 354     if (BN_is_zero(r) || BN_is_negative(r) ||
 355         BN_ucmp(r, dsa->params.q) >= 0) {
 356         ret = 0;
 357         goto err;
 358     }
 359     if (BN_is_zero(s) || BN_is_negative(s) ||
 360         BN_ucmp(s, dsa->params.q) >= 0) {
 361         ret = 0;
 362         goto err;
 363     }
 364
 365     /*
 366      * Calculate W = inv(S) mod Q save W in u2
 367      */
 368     if ((BN_mod_inverse(u2, s, dsa->params.q, ctx)) == NULL)
 369         goto err;
 370
 371     /* save M in u1 */
 372     if (dgst_len > (i >> 3))
 373         /*
 374          * if the digest length is greater than the size of q use the
 375          * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,
 376          * 4.2
 377          */
 378         dgst_len = (i >> 3);
 379     if (BN_bin2bn(dgst, dgst_len, u1) == NULL)
 380         goto err;
 381
 382     /* u1 = M * w mod q */
 383     if (!BN_mod_mul(u1, u1, u2, dsa->params.q, ctx))
 384         goto err;
 385
 386     /* u2 = r * w mod q */
 387     if (!BN_mod_mul(u2, r, u2, dsa->params.q, ctx))
 388         goto err;
 389
 390     if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {
 391         mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,
 392                                       dsa->lock, dsa->params.p, ctx);
 393         if (!mont)
 394             goto err;
 395     }
 396
 397     if (dsa->meth->dsa_mod_exp != NULL) {
 398         if (!dsa->meth->dsa_mod_exp(dsa, t1, dsa->params.g, u1, dsa->pub_key, u2,
 399                                     dsa->params.p, ctx, mont))
 400             goto err;
 401     } else {
 402         if (!BN_mod_exp2_mont(t1, dsa->params.g, u1, dsa->pub_key, u2,
 403                               dsa->params.p, ctx, mont))
 404             goto err;
 405     }
 406
 407     /* let u1 = u1 mod q */
 408     if (!BN_mod(u1, t1, dsa->params.q, ctx))
 409         goto err;
 410
 411     /*
 412      * V is now in u1.  If the signature is correct, it will be equal to R.
 413      */
 414     ret = (BN_ucmp(u1, r) == 0);
 415
 416  err:
 417     if (ret < 0)
 418         DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);
 419     BN_CTX_free(ctx);
 420     BN_free(u1);
 421     BN_free(u2);
 422     BN_free(t1);
 423     return ret;
 424 }
 425
 426 static int dsa_init(DSA *dsa)
 427 {
 428     dsa->flags |= DSA_FLAG_CACHE_MONT_P;
 429     ffc_params_init(&dsa->params);
 430     dsa->dirty_cnt++;
 431     return 1;
 432 }
 433
 434 static int dsa_finish(DSA *dsa)
 435 {
 436     BN_MONT_CTX_free(dsa->method_mont_p);
 437     return 1;
 438 }
 439
 440 /*
 441  * Compute the inverse of k modulo q.
 442  * Since q is prime, Fermat's Little Theorem applies, which reduces this to
 443  * mod-exp operation.  Both the exponent and modulus are public information
 444  * so a mod-exp that doesn't leak the base is sufficient.  A newly allocated
 445  * BIGNUM is returned which the caller must free.
 446  */
 447 static BIGNUM *dsa_mod_inverse_fermat(const BIGNUM *k, const BIGNUM *q,
 448                                       BN_CTX *ctx)
 449 {
 450     BIGNUM *res = NULL;
 451     BIGNUM *r, *e;
 452
 453     if ((r = BN_new()) == NULL)
 454         return NULL;
 455
 456     BN_CTX_start(ctx);
 457     if ((e = BN_CTX_get(ctx)) != NULL
 458             && BN_set_word(r, 2)
 459             && BN_sub(e, q, r)
 460             && BN_mod_exp_mont(r, k, e, q, ctx, NULL))
 461         res = r;
 462     else
 463         BN_free(r);
 464     BN_CTX_end(ctx);
 465     return res;
 466 }