crypto/rsa/rsa_ossl.c

   1 /*
   2  * Copyright 1995-2018 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 #include "internal/cryptlib.h"
  11 #include "crypto/bn.h"
  12 #include "rsa_local.h"
  13 #include "internal/constant_time.h"
  14
  15 static int rsa_ossl_public_encrypt(int flen, const unsigned char *from,
  16                                   unsigned char *to, RSA *rsa, int padding);
  17 static int rsa_ossl_private_encrypt(int flen, const unsigned char *from,
  18                                    unsigned char *to, RSA *rsa, int padding);
  19 static int rsa_ossl_public_decrypt(int flen, const unsigned char *from,
  20                                   unsigned char *to, RSA *rsa, int padding);
  21 static int rsa_ossl_private_decrypt(int flen, const unsigned char *from,
  22                                    unsigned char *to, RSA *rsa, int padding);
  23 static int rsa_ossl_mod_exp(BIGNUM *r0, const BIGNUM *i, RSA *rsa,
  24                            BN_CTX *ctx);
  25 static int rsa_ossl_init(RSA *rsa);
  26 static int rsa_ossl_finish(RSA *rsa);
  27 static RSA_METHOD rsa_pkcs1_ossl_meth = {
  28     "OpenSSL PKCS#1 RSA",
  29     rsa_ossl_public_encrypt,
  30     rsa_ossl_public_decrypt,     /* signature verification */
  31     rsa_ossl_private_encrypt,    /* signing */
  32     rsa_ossl_private_decrypt,
  33     rsa_ossl_mod_exp,
  34     BN_mod_exp_mont,            /* XXX probably we should not use Montgomery
  35                                  * if e == 3 */
  36     rsa_ossl_init,
  37     rsa_ossl_finish,
  38     RSA_FLAG_FIPS_METHOD,       /* flags */
  39     NULL,
  40     0,                          /* rsa_sign */
  41     0,                          /* rsa_verify */
  42     NULL,                       /* rsa_keygen */
  43     NULL                        /* rsa_multi_prime_keygen */
  44 };
  45
  46 static const RSA_METHOD *default_RSA_meth = &rsa_pkcs1_ossl_meth;
  47
  48 void RSA_set_default_method(const RSA_METHOD *meth)
  49 {
  50     default_RSA_meth = meth;
  51 }
  52
  53 const RSA_METHOD *RSA_get_default_method(void)
  54 {
  55     return default_RSA_meth;
  56 }
  57
  58 const RSA_METHOD *RSA_PKCS1_OpenSSL(void)
  59 {
  60     return &rsa_pkcs1_ossl_meth;
  61 }
  62
  63 const RSA_METHOD *RSA_null_method(void)
  64 {
  65     return NULL;
  66 }
  67
  68 static int rsa_ossl_public_encrypt(int flen, const unsigned char *from,
  69                                   unsigned char *to, RSA *rsa, int padding)
  70 {
  71     BIGNUM *f, *ret;
  72     int i, num = 0, r = -1;
  73     unsigned char *buf = NULL;
  74     BN_CTX *ctx = NULL;
  75
  76     if (BN_num_bits(rsa->n) > OPENSSL_RSA_MAX_MODULUS_BITS) {
  77         RSAerr(RSA_F_RSA_OSSL_PUBLIC_ENCRYPT, RSA_R_MODULUS_TOO_LARGE);
  78         return -1;
  79     }
  80
  81     if (BN_ucmp(rsa->n, rsa->e) <= 0) {
  82         RSAerr(RSA_F_RSA_OSSL_PUBLIC_ENCRYPT, RSA_R_BAD_E_VALUE);
  83         return -1;
  84     }
  85
  86     /* for large moduli, enforce exponent limit */
  87     if (BN_num_bits(rsa->n) > OPENSSL_RSA_SMALL_MODULUS_BITS) {
  88         if (BN_num_bits(rsa->e) > OPENSSL_RSA_MAX_PUBEXP_BITS) {
  89             RSAerr(RSA_F_RSA_OSSL_PUBLIC_ENCRYPT, RSA_R_BAD_E_VALUE);
  90             return -1;
  91         }
  92     }
  93
  94     if ((ctx = BN_CTX_new_ex(rsa->libctx)) == NULL)
  95         goto err;
  96     BN_CTX_start(ctx);
  97     f = BN_CTX_get(ctx);
  98     ret = BN_CTX_get(ctx);
  99     num = BN_num_bytes(rsa->n);
 100     buf = OPENSSL_malloc(num);
 101     if (ret == NULL || buf == NULL) {
 102         RSAerr(RSA_F_RSA_OSSL_PUBLIC_ENCRYPT, ERR_R_MALLOC_FAILURE);
 103         goto err;
 104     }
 105
 106     switch (padding) {
 107     case RSA_PKCS1_PADDING:
 108         i = RSA_padding_add_PKCS1_type_2(buf, num, from, flen);
 109         break;
 110     case RSA_PKCS1_OAEP_PADDING:
 111         i = RSA_padding_add_PKCS1_OAEP(buf, num, from, flen, NULL, 0);
 112         break;
 113 #ifndef FIPS_MODE
 114     case RSA_SSLV23_PADDING:
 115         i = RSA_padding_add_SSLv23(buf, num, from, flen);
 116         break;
 117 #endif
 118     case RSA_NO_PADDING:
 119         i = RSA_padding_add_none(buf, num, from, flen);
 120         break;
 121     default:
 122         RSAerr(RSA_F_RSA_OSSL_PUBLIC_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
 123         goto err;
 124     }
 125     if (i <= 0)
 126         goto err;
 127
 128     if (BN_bin2bn(buf, num, f) == NULL)
 129         goto err;
 130
 131     if (BN_ucmp(f, rsa->n) >= 0) {
 132         /* usually the padding functions would catch this */
 133         RSAerr(RSA_F_RSA_OSSL_PUBLIC_ENCRYPT,
 134                RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
 135         goto err;
 136     }
 137
 138     if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
 139         if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock,
 140                                     rsa->n, ctx))
 141             goto err;
 142
 143     if (!rsa->meth->bn_mod_exp(ret, f, rsa->e, rsa->n, ctx,
 144                                rsa->_method_mod_n))
 145         goto err;
 146
 147     /*
 148      * BN_bn2binpad puts in leading 0 bytes if the number is less than
 149      * the length of the modulus.
 150      */
 151     r = BN_bn2binpad(ret, to, num);
 152  err:
 153     BN_CTX_end(ctx);
 154     BN_CTX_free(ctx);
 155     OPENSSL_clear_free(buf, num);
 156     return r;
 157 }
 158
 159 static BN_BLINDING *rsa_get_blinding(RSA *rsa, int *local, BN_CTX *ctx)
 160 {
 161     BN_BLINDING *ret;
 162
 163     CRYPTO_THREAD_write_lock(rsa->lock);
 164
 165     if (rsa->blinding == NULL) {
 166         rsa->blinding = RSA_setup_blinding(rsa, ctx);
 167     }
 168
 169     ret = rsa->blinding;
 170     if (ret == NULL)
 171         goto err;
 172
 173     if (BN_BLINDING_is_current_thread(ret)) {
 174         /* rsa->blinding is ours! */
 175
 176         *local = 1;
 177     } else {
 178         /* resort to rsa->mt_blinding instead */
 179
 180         /*
 181          * instructs rsa_blinding_convert(), rsa_blinding_invert() that the
 182          * BN_BLINDING is shared, meaning that accesses require locks, and
 183          * that the blinding factor must be stored outside the BN_BLINDING
 184          */
 185         *local = 0;
 186
 187         if (rsa->mt_blinding == NULL) {
 188             rsa->mt_blinding = RSA_setup_blinding(rsa, ctx);
 189         }
 190         ret = rsa->mt_blinding;
 191     }
 192
 193  err:
 194     CRYPTO_THREAD_unlock(rsa->lock);
 195     return ret;
 196 }
 197
 198 static int rsa_blinding_convert(BN_BLINDING *b, BIGNUM *f, BIGNUM *unblind,
 199                                 BN_CTX *ctx)
 200 {
 201     if (unblind == NULL) {
 202         /*
 203          * Local blinding: store the unblinding factor in BN_BLINDING.
 204          */
 205         return BN_BLINDING_convert_ex(f, NULL, b, ctx);
 206     } else {
 207         /*
 208          * Shared blinding: store the unblinding factor outside BN_BLINDING.
 209          */
 210         int ret;
 211
 212         BN_BLINDING_lock(b);
 213         ret = BN_BLINDING_convert_ex(f, unblind, b, ctx);
 214         BN_BLINDING_unlock(b);
 215
 216         return ret;
 217     }
 218 }
 219
 220 static int rsa_blinding_invert(BN_BLINDING *b, BIGNUM *f, BIGNUM *unblind,
 221                                BN_CTX *ctx)
 222 {
 223     /*
 224      * For local blinding, unblind is set to NULL, and BN_BLINDING_invert_ex
 225      * will use the unblinding factor stored in BN_BLINDING. If BN_BLINDING
 226      * is shared between threads, unblind must be non-null:
 227      * BN_BLINDING_invert_ex will then use the local unblinding factor, and
 228      * will only read the modulus from BN_BLINDING. In both cases it's safe
 229      * to access the blinding without a lock.
 230      */
 231     return BN_BLINDING_invert_ex(f, unblind, b, ctx);
 232 }
 233
 234 /* signing */
 235 static int rsa_ossl_private_encrypt(int flen, const unsigned char *from,
 236                                    unsigned char *to, RSA *rsa, int padding)
 237 {
 238     BIGNUM *f, *ret, *res;
 239     int i, num = 0, r = -1;
 240     unsigned char *buf = NULL;
 241     BN_CTX *ctx = NULL;
 242     int local_blinding = 0;
 243     /*
 244      * Used only if the blinding structure is shared. A non-NULL unblind
 245      * instructs rsa_blinding_convert() and rsa_blinding_invert() to store
 246      * the unblinding factor outside the blinding structure.
 247      */
 248     BIGNUM *unblind = NULL;
 249     BN_BLINDING *blinding = NULL;
 250
 251     if ((ctx = BN_CTX_new_ex(rsa->libctx)) == NULL)
 252         goto err;
 253     BN_CTX_start(ctx);
 254     f = BN_CTX_get(ctx);
 255     ret = BN_CTX_get(ctx);
 256     num = BN_num_bytes(rsa->n);
 257     buf = OPENSSL_malloc(num);
 258     if (ret == NULL || buf == NULL) {
 259         RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, ERR_R_MALLOC_FAILURE);
 260         goto err;
 261     }
 262
 263     switch (padding) {
 264     case RSA_PKCS1_PADDING:
 265         i = RSA_padding_add_PKCS1_type_1(buf, num, from, flen);
 266         break;
 267     case RSA_X931_PADDING:
 268         i = RSA_padding_add_X931(buf, num, from, flen);
 269         break;
 270     case RSA_NO_PADDING:
 271         i = RSA_padding_add_none(buf, num, from, flen);
 272         break;
 273     case RSA_SSLV23_PADDING:
 274     default:
 275         RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
 276         goto err;
 277     }
 278     if (i <= 0)
 279         goto err;
 280
 281     if (BN_bin2bn(buf, num, f) == NULL)
 282         goto err;
 283
 284     if (BN_ucmp(f, rsa->n) >= 0) {
 285         /* usually the padding functions would catch this */
 286         RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT,
 287                RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
 288         goto err;
 289     }
 290
 291     if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
 292         if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock,
 293                                     rsa->n, ctx))
 294             goto err;
 295
 296     if (!(rsa->flags & RSA_FLAG_NO_BLINDING)) {
 297         blinding = rsa_get_blinding(rsa, &local_blinding, ctx);
 298         if (blinding == NULL) {
 299             RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, ERR_R_INTERNAL_ERROR);
 300             goto err;
 301         }
 302     }
 303
 304     if (blinding != NULL) {
 305         if (!local_blinding && ((unblind = BN_CTX_get(ctx)) == NULL)) {
 306             RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, ERR_R_MALLOC_FAILURE);
 307             goto err;
 308         }
 309         if (!rsa_blinding_convert(blinding, f, unblind, ctx))
 310             goto err;
 311     }
 312
 313     if ((rsa->flags & RSA_FLAG_EXT_PKEY) ||
 314         (rsa->version == RSA_ASN1_VERSION_MULTI) ||
 315         ((rsa->p != NULL) &&
 316          (rsa->q != NULL) &&
 317          (rsa->dmp1 != NULL) && (rsa->dmq1 != NULL) && (rsa->iqmp != NULL))) {
 318         if (!rsa->meth->rsa_mod_exp(ret, f, rsa, ctx))
 319             goto err;
 320     } else {
 321         BIGNUM *d = BN_new();
 322         if (d == NULL) {
 323             RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, ERR_R_MALLOC_FAILURE);
 324             goto err;
 325         }
 326         if (rsa->d == NULL) {
 327             RSAerr(RSA_F_RSA_OSSL_PRIVATE_ENCRYPT, RSA_R_MISSING_PRIVATE_KEY);
 328             BN_free(d);
 329             goto err;
 330         }
 331         BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
 332
 333         if (!rsa->meth->bn_mod_exp(ret, f, d, rsa->n, ctx,
 334                                    rsa->_method_mod_n)) {
 335             BN_free(d);
 336             goto err;
 337         }
 338         /* We MUST free d before any further use of rsa->d */
 339         BN_free(d);
 340     }
 341
 342     if (blinding)
 343         if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
 344             goto err;
 345
 346     if (padding == RSA_X931_PADDING) {
 347         if (!BN_sub(f, rsa->n, ret))
 348             goto err;
 349         if (BN_cmp(ret, f) > 0)
 350             res = f;
 351         else
 352             res = ret;
 353     } else {
 354         res = ret;
 355     }
 356
 357     /*
 358      * BN_bn2binpad puts in leading 0 bytes if the number is less than
 359      * the length of the modulus.
 360      */
 361     r = BN_bn2binpad(res, to, num);
 362  err:
 363     BN_CTX_end(ctx);
 364     BN_CTX_free(ctx);
 365     OPENSSL_clear_free(buf, num);
 366     return r;
 367 }
 368
 369 static int rsa_ossl_private_decrypt(int flen, const unsigned char *from,
 370                                    unsigned char *to, RSA *rsa, int padding)
 371 {
 372     BIGNUM *f, *ret;
 373     int j, num = 0, r = -1;
 374     unsigned char *buf = NULL;
 375     BN_CTX *ctx = NULL;
 376     int local_blinding = 0;
 377     /*
 378      * Used only if the blinding structure is shared. A non-NULL unblind
 379      * instructs rsa_blinding_convert() and rsa_blinding_invert() to store
 380      * the unblinding factor outside the blinding structure.
 381      */
 382     BIGNUM *unblind = NULL;
 383     BN_BLINDING *blinding = NULL;
 384
 385     if ((ctx = BN_CTX_new_ex(rsa->libctx)) == NULL)
 386         goto err;
 387     BN_CTX_start(ctx);
 388     f = BN_CTX_get(ctx);
 389     ret = BN_CTX_get(ctx);
 390     num = BN_num_bytes(rsa->n);
 391     buf = OPENSSL_malloc(num);
 392     if (ret == NULL || buf == NULL) {
 393         RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, ERR_R_MALLOC_FAILURE);
 394         goto err;
 395     }
 396
 397     /*
 398      * This check was for equality but PGP does evil things and chops off the
 399      * top '0' bytes
 400      */
 401     if (flen > num) {
 402         RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT,
 403                RSA_R_DATA_GREATER_THAN_MOD_LEN);
 404         goto err;
 405     }
 406
 407     /* make data into a big number */
 408     if (BN_bin2bn(from, (int)flen, f) == NULL)
 409         goto err;
 410
 411     if (BN_ucmp(f, rsa->n) >= 0) {
 412         RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT,
 413                RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
 414         goto err;
 415     }
 416
 417     if (!(rsa->flags & RSA_FLAG_NO_BLINDING)) {
 418         blinding = rsa_get_blinding(rsa, &local_blinding, ctx);
 419         if (blinding == NULL) {
 420             RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, ERR_R_INTERNAL_ERROR);
 421             goto err;
 422         }
 423     }
 424
 425     if (blinding != NULL) {
 426         if (!local_blinding && ((unblind = BN_CTX_get(ctx)) == NULL)) {
 427             RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, ERR_R_MALLOC_FAILURE);
 428             goto err;
 429         }
 430         if (!rsa_blinding_convert(blinding, f, unblind, ctx))
 431             goto err;
 432     }
 433
 434     /* do the decrypt */
 435     if ((rsa->flags & RSA_FLAG_EXT_PKEY) ||
 436         (rsa->version == RSA_ASN1_VERSION_MULTI) ||
 437         ((rsa->p != NULL) &&
 438          (rsa->q != NULL) &&
 439          (rsa->dmp1 != NULL) && (rsa->dmq1 != NULL) && (rsa->iqmp != NULL))) {
 440         if (!rsa->meth->rsa_mod_exp(ret, f, rsa, ctx))
 441             goto err;
 442     } else {
 443         BIGNUM *d = BN_new();
 444         if (d == NULL) {
 445             RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, ERR_R_MALLOC_FAILURE);
 446             goto err;
 447         }
 448         if (rsa->d == NULL) {
 449             RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, RSA_R_MISSING_PRIVATE_KEY);
 450             BN_free(d);
 451             goto err;
 452         }
 453         BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
 454
 455         if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
 456             if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock,
 457                                         rsa->n, ctx)) {
 458                 BN_free(d);
 459                 goto err;
 460             }
 461         if (!rsa->meth->bn_mod_exp(ret, f, d, rsa->n, ctx,
 462                                    rsa->_method_mod_n)) {
 463             BN_free(d);
 464             goto err;
 465         }
 466         /* We MUST free d before any further use of rsa->d */
 467         BN_free(d);
 468     }
 469
 470     if (blinding)
 471         if (!rsa_blinding_invert(blinding, ret, unblind, ctx))
 472             goto err;
 473
 474     j = BN_bn2binpad(ret, buf, num);
 475     if (j < 0)
 476         goto err;
 477
 478     switch (padding) {
 479     case RSA_PKCS1_PADDING:
 480         r = RSA_padding_check_PKCS1_type_2(to, num, buf, j, num);
 481         break;
 482     case RSA_PKCS1_OAEP_PADDING:
 483         r = RSA_padding_check_PKCS1_OAEP(to, num, buf, j, num, NULL, 0);
 484         break;
 485 #ifndef FIPS_MODE
 486     case RSA_SSLV23_PADDING:
 487         r = RSA_padding_check_SSLv23(to, num, buf, j, num);
 488         break;
 489 #endif
 490     case RSA_NO_PADDING:
 491         memcpy(to, buf, (r = j));
 492         break;
 493     default:
 494         RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
 495         goto err;
 496     }
 497 #ifndef FIPS_MODE
 498     /*
 499      * This trick doesn't work in the FIPS provider because libcrypto manages
 500      * the error stack. Instead we opt not to put an error on the stack at all
 501      * in case of padding failure in the FIPS provider.
 502      */
 503     RSAerr(RSA_F_RSA_OSSL_PRIVATE_DECRYPT, RSA_R_PADDING_CHECK_FAILED);
 504     err_clear_last_constant_time(1 & ~constant_time_msb(r));
 505 #endif
 506
 507  err:
 508     BN_CTX_end(ctx);
 509     BN_CTX_free(ctx);
 510     OPENSSL_clear_free(buf, num);
 511     return r;
 512 }
 513
 514 /* signature verification */
 515 static int rsa_ossl_public_decrypt(int flen, const unsigned char *from,
 516                                   unsigned char *to, RSA *rsa, int padding)
 517 {
 518     BIGNUM *f, *ret;
 519     int i, num = 0, r = -1;
 520     unsigned char *buf = NULL;
 521     BN_CTX *ctx = NULL;
 522
 523     if (BN_num_bits(rsa->n) > OPENSSL_RSA_MAX_MODULUS_BITS) {
 524         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_MODULUS_TOO_LARGE);
 525         return -1;
 526     }
 527
 528     if (BN_ucmp(rsa->n, rsa->e) <= 0) {
 529         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_BAD_E_VALUE);
 530         return -1;
 531     }
 532
 533     /* for large moduli, enforce exponent limit */
 534     if (BN_num_bits(rsa->n) > OPENSSL_RSA_SMALL_MODULUS_BITS) {
 535         if (BN_num_bits(rsa->e) > OPENSSL_RSA_MAX_PUBEXP_BITS) {
 536             RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_BAD_E_VALUE);
 537             return -1;
 538         }
 539     }
 540
 541     if ((ctx = BN_CTX_new_ex(rsa->libctx)) == NULL)
 542         goto err;
 543     BN_CTX_start(ctx);
 544     f = BN_CTX_get(ctx);
 545     ret = BN_CTX_get(ctx);
 546     num = BN_num_bytes(rsa->n);
 547     buf = OPENSSL_malloc(num);
 548     if (ret == NULL || buf == NULL) {
 549         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, ERR_R_MALLOC_FAILURE);
 550         goto err;
 551     }
 552
 553     /*
 554      * This check was for equality but PGP does evil things and chops off the
 555      * top '0' bytes
 556      */
 557     if (flen > num) {
 558         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_DATA_GREATER_THAN_MOD_LEN);
 559         goto err;
 560     }
 561
 562     if (BN_bin2bn(from, flen, f) == NULL)
 563         goto err;
 564
 565     if (BN_ucmp(f, rsa->n) >= 0) {
 566         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT,
 567                RSA_R_DATA_TOO_LARGE_FOR_MODULUS);
 568         goto err;
 569     }
 570
 571     if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
 572         if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock,
 573                                     rsa->n, ctx))
 574             goto err;
 575
 576     if (!rsa->meth->bn_mod_exp(ret, f, rsa->e, rsa->n, ctx,
 577                                rsa->_method_mod_n))
 578         goto err;
 579
 580     if ((padding == RSA_X931_PADDING) && ((bn_get_words(ret)[0] & 0xf) != 12))
 581         if (!BN_sub(ret, rsa->n, ret))
 582             goto err;
 583
 584     i = BN_bn2binpad(ret, buf, num);
 585     if (i < 0)
 586         goto err;
 587
 588     switch (padding) {
 589     case RSA_PKCS1_PADDING:
 590         r = RSA_padding_check_PKCS1_type_1(to, num, buf, i, num);
 591         break;
 592     case RSA_X931_PADDING:
 593         r = RSA_padding_check_X931(to, num, buf, i, num);
 594         break;
 595     case RSA_NO_PADDING:
 596         memcpy(to, buf, (r = i));
 597         break;
 598     default:
 599         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_UNKNOWN_PADDING_TYPE);
 600         goto err;
 601     }
 602     if (r < 0)
 603         RSAerr(RSA_F_RSA_OSSL_PUBLIC_DECRYPT, RSA_R_PADDING_CHECK_FAILED);
 604
 605  err:
 606     BN_CTX_end(ctx);
 607     BN_CTX_free(ctx);
 608     OPENSSL_clear_free(buf, num);
 609     return r;
 610 }
 611
 612 static int rsa_ossl_mod_exp(BIGNUM *r0, const BIGNUM *I, RSA *rsa, BN_CTX *ctx)
 613 {
 614     BIGNUM *r1, *m1, *vrfy;
 615     int ret = 0, smooth = 0;
 616 #ifndef FIPS_MODE
 617     BIGNUM *r2, *m[RSA_MAX_PRIME_NUM - 2];
 618     int i, ex_primes = 0;
 619     RSA_PRIME_INFO *pinfo;
 620 #endif
 621
 622     BN_CTX_start(ctx);
 623
 624     r1 = BN_CTX_get(ctx);
 625 #ifndef FIPS_MODE
 626     r2 = BN_CTX_get(ctx);
 627 #endif
 628     m1 = BN_CTX_get(ctx);
 629     vrfy = BN_CTX_get(ctx);
 630     if (vrfy == NULL)
 631         goto err;
 632
 633 #ifndef FIPS_MODE
 634     if (rsa->version == RSA_ASN1_VERSION_MULTI
 635         && ((ex_primes = sk_RSA_PRIME_INFO_num(rsa->prime_infos)) <= 0
 636              || ex_primes > RSA_MAX_PRIME_NUM - 2))
 637         goto err;
 638 #endif
 639
 640     if (rsa->flags & RSA_FLAG_CACHE_PRIVATE) {
 641         BIGNUM *factor = BN_new();
 642
 643         if (factor == NULL)
 644             goto err;
 645
 646         /*
 647          * Make sure BN_mod_inverse in Montgomery initialization uses the
 648          * BN_FLG_CONSTTIME flag
 649          */
 650         if (!(BN_with_flags(factor, rsa->p, BN_FLG_CONSTTIME),
 651               BN_MONT_CTX_set_locked(&rsa->_method_mod_p, rsa->lock,
 652                                      factor, ctx))
 653             || !(BN_with_flags(factor, rsa->q, BN_FLG_CONSTTIME),
 654                  BN_MONT_CTX_set_locked(&rsa->_method_mod_q, rsa->lock,
 655                                         factor, ctx))) {
 656             BN_free(factor);
 657             goto err;
 658         }
 659 #ifndef FIPS_MODE
 660         for (i = 0; i < ex_primes; i++) {
 661             pinfo = sk_RSA_PRIME_INFO_value(rsa->prime_infos, i);
 662             BN_with_flags(factor, pinfo->r, BN_FLG_CONSTTIME);
 663             if (!BN_MONT_CTX_set_locked(&pinfo->m, rsa->lock, factor, ctx)) {
 664                 BN_free(factor);
 665                 goto err;
 666             }
 667         }
 668 #endif
 669         /*
 670          * We MUST free |factor| before any further use of the prime factors
 671          */
 672         BN_free(factor);
 673
 674         smooth = (rsa->meth->bn_mod_exp == BN_mod_exp_mont)
 675 #ifndef FIPS_MODE
 676                  && (ex_primes == 0)
 677 #endif
 678                  && (BN_num_bits(rsa->q) == BN_num_bits(rsa->p));
 679     }
 680
 681     if (rsa->flags & RSA_FLAG_CACHE_PUBLIC)
 682         if (!BN_MONT_CTX_set_locked(&rsa->_method_mod_n, rsa->lock,
 683                                     rsa->n, ctx))
 684             goto err;
 685
 686     if (smooth) {
 687         /*
 688          * Conversion from Montgomery domain, a.k.a. Montgomery reduction,
 689          * accepts values in [0-m*2^w) range. w is m's bit width rounded up
 690          * to limb width. So that at the very least if |I| is fully reduced,
 691          * i.e. less than p*q, we can count on from-to round to perform
 692          * below modulo operations on |I|. Unlike BN_mod it's constant time.
 693          */
 694         if (/* m1 = I moq q */
 695             !bn_from_mont_fixed_top(m1, I, rsa->_method_mod_q, ctx)
 696             || !bn_to_mont_fixed_top(m1, m1, rsa->_method_mod_q, ctx)
 697             /* m1 = m1^dmq1 mod q */
 698             || !BN_mod_exp_mont_consttime(m1, m1, rsa->dmq1, rsa->q, ctx,
 699                                           rsa->_method_mod_q)
 700             /* r1 = I mod p */
 701             || !bn_from_mont_fixed_top(r1, I, rsa->_method_mod_p, ctx)
 702             || !bn_to_mont_fixed_top(r1, r1, rsa->_method_mod_p, ctx)
 703             /* r1 = r1^dmp1 mod p */
 704             || !BN_mod_exp_mont_consttime(r1, r1, rsa->dmp1, rsa->p, ctx,
 705                                           rsa->_method_mod_p)
 706             /* r1 = (r1 - m1) mod p */
 707             /*
 708              * bn_mod_sub_fixed_top is not regular modular subtraction,
 709              * it can tolerate subtrahend to be larger than modulus, but
 710              * not bit-wise wider. This makes up for uncommon q>p case,
 711              * when |m1| can be larger than |rsa->p|.
 712              */
 713             || !bn_mod_sub_fixed_top(r1, r1, m1, rsa->p)
 714
 715             /* r1 = r1 * iqmp mod p */
 716             || !bn_to_mont_fixed_top(r1, r1, rsa->_method_mod_p, ctx)
 717             || !bn_mul_mont_fixed_top(r1, r1, rsa->iqmp, rsa->_method_mod_p,
 718                                       ctx)
 719             /* r0 = r1 * q + m1 */
 720             || !bn_mul_fixed_top(r0, r1, rsa->q, ctx)
 721             || !bn_mod_add_fixed_top(r0, r0, m1, rsa->n))
 722             goto err;
 723
 724         goto tail;
 725     }
 726
 727     /* compute I mod q */
 728     {
 729         BIGNUM *c = BN_new();
 730         if (c == NULL)
 731             goto err;
 732         BN_with_flags(c, I, BN_FLG_CONSTTIME);
 733
 734         if (!BN_mod(r1, c, rsa->q, ctx)) {
 735             BN_free(c);
 736             goto err;
 737         }
 738
 739         {
 740             BIGNUM *dmq1 = BN_new();
 741             if (dmq1 == NULL) {
 742                 BN_free(c);
 743                 goto err;
 744             }
 745             BN_with_flags(dmq1, rsa->dmq1, BN_FLG_CONSTTIME);
 746
 747             /* compute r1^dmq1 mod q */
 748             if (!rsa->meth->bn_mod_exp(m1, r1, dmq1, rsa->q, ctx,
 749                                        rsa->_method_mod_q)) {
 750                 BN_free(c);
 751                 BN_free(dmq1);
 752                 goto err;
 753             }
 754             /* We MUST free dmq1 before any further use of rsa->dmq1 */
 755             BN_free(dmq1);
 756         }
 757
 758         /* compute I mod p */
 759         if (!BN_mod(r1, c, rsa->p, ctx)) {
 760             BN_free(c);
 761             goto err;
 762         }
 763         /* We MUST free c before any further use of I */
 764         BN_free(c);
 765     }
 766
 767     {
 768         BIGNUM *dmp1 = BN_new();
 769         if (dmp1 == NULL)
 770             goto err;
 771         BN_with_flags(dmp1, rsa->dmp1, BN_FLG_CONSTTIME);
 772
 773         /* compute r1^dmp1 mod p */
 774         if (!rsa->meth->bn_mod_exp(r0, r1, dmp1, rsa->p, ctx,
 775                                    rsa->_method_mod_p)) {
 776             BN_free(dmp1);
 777             goto err;
 778         }
 779         /* We MUST free dmp1 before any further use of rsa->dmp1 */
 780         BN_free(dmp1);
 781     }
 782
 783 #ifndef FIPS_MODE
 784     /*
 785      * calculate m_i in multi-prime case
 786      *
 787      * TODO:
 788      * 1. squash the following two loops and calculate |m_i| there.
 789      * 2. remove cc and reuse |c|.
 790      * 3. remove |dmq1| and |dmp1| in previous block and use |di|.
 791      *
 792      * If these things are done, the code will be more readable.
 793      */
 794     if (ex_primes > 0) {
 795         BIGNUM *di = BN_new(), *cc = BN_new();
 796
 797         if (cc == NULL || di == NULL) {
 798             BN_free(cc);
 799             BN_free(di);
 800             goto err;
 801         }
 802
 803         for (i = 0; i < ex_primes; i++) {
 804             /* prepare m_i */
 805             if ((m[i] = BN_CTX_get(ctx)) == NULL) {
 806                 BN_free(cc);
 807                 BN_free(di);
 808                 goto err;
 809             }
 810
 811             pinfo = sk_RSA_PRIME_INFO_value(rsa->prime_infos, i);
 812
 813             /* prepare c and d_i */
 814             BN_with_flags(cc, I, BN_FLG_CONSTTIME);
 815             BN_with_flags(di, pinfo->d, BN_FLG_CONSTTIME);
 816
 817             if (!BN_mod(r1, cc, pinfo->r, ctx)) {
 818                 BN_free(cc);
 819                 BN_free(di);
 820                 goto err;
 821             }
 822             /* compute r1 ^ d_i mod r_i */
 823             if (!rsa->meth->bn_mod_exp(m[i], r1, di, pinfo->r, ctx, pinfo->m)) {
 824                 BN_free(cc);
 825                 BN_free(di);
 826                 goto err;
 827             }
 828         }
 829
 830         BN_free(cc);
 831         BN_free(di);
 832     }
 833 #endif
 834
 835     if (!BN_sub(r0, r0, m1))
 836         goto err;
 837     /*
 838      * This will help stop the size of r0 increasing, which does affect the
 839      * multiply if it optimised for a power of 2 size
 840      */
 841     if (BN_is_negative(r0))
 842         if (!BN_add(r0, r0, rsa->p))
 843             goto err;
 844
 845     if (!BN_mul(r1, r0, rsa->iqmp, ctx))
 846         goto err;
 847
 848     {
 849         BIGNUM *pr1 = BN_new();
 850         if (pr1 == NULL)
 851             goto err;
 852         BN_with_flags(pr1, r1, BN_FLG_CONSTTIME);
 853
 854         if (!BN_mod(r0, pr1, rsa->p, ctx)) {
 855             BN_free(pr1);
 856             goto err;
 857         }
 858         /* We MUST free pr1 before any further use of r1 */
 859         BN_free(pr1);
 860     }
 861
 862     /*
 863      * If p < q it is occasionally possible for the correction of adding 'p'
 864      * if r0 is negative above to leave the result still negative. This can
 865      * break the private key operations: the following second correction
 866      * should *always* correct this rare occurrence. This will *never* happen
 867      * with OpenSSL generated keys because they ensure p > q [steve]
 868      */
 869     if (BN_is_negative(r0))
 870         if (!BN_add(r0, r0, rsa->p))
 871             goto err;
 872     if (!BN_mul(r1, r0, rsa->q, ctx))
 873         goto err;
 874     if (!BN_add(r0, r1, m1))
 875         goto err;
 876
 877 #ifndef FIPS_MODE
 878     /* add m_i to m in multi-prime case */
 879     if (ex_primes > 0) {
 880         BIGNUM *pr2 = BN_new();
 881
 882         if (pr2 == NULL)
 883             goto err;
 884
 885         for (i = 0; i < ex_primes; i++) {
 886             pinfo = sk_RSA_PRIME_INFO_value(rsa->prime_infos, i);
 887             if (!BN_sub(r1, m[i], r0)) {
 888                 BN_free(pr2);
 889                 goto err;
 890             }
 891
 892             if (!BN_mul(r2, r1, pinfo->t, ctx)) {
 893                 BN_free(pr2);
 894                 goto err;
 895             }
 896
 897             BN_with_flags(pr2, r2, BN_FLG_CONSTTIME);
 898
 899             if (!BN_mod(r1, pr2, pinfo->r, ctx)) {
 900                 BN_free(pr2);
 901                 goto err;
 902             }
 903
 904             if (BN_is_negative(r1))
 905                 if (!BN_add(r1, r1, pinfo->r)) {
 906                     BN_free(pr2);
 907                     goto err;
 908                 }
 909             if (!BN_mul(r1, r1, pinfo->pp, ctx)) {
 910                 BN_free(pr2);
 911                 goto err;
 912             }
 913             if (!BN_add(r0, r0, r1)) {
 914                 BN_free(pr2);
 915                 goto err;
 916             }
 917         }
 918         BN_free(pr2);
 919     }
 920 #endif
 921
 922  tail:
 923     if (rsa->e && rsa->n) {
 924         if (rsa->meth->bn_mod_exp == BN_mod_exp_mont) {
 925             if (!BN_mod_exp_mont(vrfy, r0, rsa->e, rsa->n, ctx,
 926                                  rsa->_method_mod_n))
 927                 goto err;
 928         } else {
 929             bn_correct_top(r0);
 930             if (!rsa->meth->bn_mod_exp(vrfy, r0, rsa->e, rsa->n, ctx,
 931                                        rsa->_method_mod_n))
 932                 goto err;
 933         }
 934         /*
 935          * If 'I' was greater than (or equal to) rsa->n, the operation will
 936          * be equivalent to using 'I mod n'. However, the result of the
 937          * verify will *always* be less than 'n' so we don't check for
 938          * absolute equality, just congruency.
 939          */
 940         if (!BN_sub(vrfy, vrfy, I))
 941             goto err;
 942         if (BN_is_zero(vrfy)) {
 943             bn_correct_top(r0);
 944             ret = 1;
 945             goto err;   /* not actually error */
 946         }
 947         if (!BN_mod(vrfy, vrfy, rsa->n, ctx))
 948             goto err;
 949         if (BN_is_negative(vrfy))
 950             if (!BN_add(vrfy, vrfy, rsa->n))
 951                 goto err;
 952         if (!BN_is_zero(vrfy)) {
 953             /*
 954              * 'I' and 'vrfy' aren't congruent mod n. Don't leak
 955              * miscalculated CRT output, just do a raw (slower) mod_exp and
 956              * return that instead.
 957              */
 958
 959             BIGNUM *d = BN_new();
 960             if (d == NULL)
 961                 goto err;
 962             BN_with_flags(d, rsa->d, BN_FLG_CONSTTIME);
 963
 964             if (!rsa->meth->bn_mod_exp(r0, I, d, rsa->n, ctx,
 965                                        rsa->_method_mod_n)) {
 966                 BN_free(d);
 967                 goto err;
 968             }
 969             /* We MUST free d before any further use of rsa->d */
 970             BN_free(d);
 971         }
 972     }
 973     /*
 974      * It's unfortunate that we have to bn_correct_top(r0). What hopefully
 975      * saves the day is that correction is highly unlike, and private key
 976      * operations are customarily performed on blinded message. Which means
 977      * that attacker won't observe correlation with chosen plaintext.
 978      * Secondly, remaining code would still handle it in same computational
 979      * time and even conceal memory access pattern around corrected top.
 980      */
 981     bn_correct_top(r0);
 982     ret = 1;
 983  err:
 984     BN_CTX_end(ctx);
 985     return ret;
 986 }
 987
 988 static int rsa_ossl_init(RSA *rsa)
 989 {
 990     rsa->flags |= RSA_FLAG_CACHE_PUBLIC | RSA_FLAG_CACHE_PRIVATE;
 991     return 1;
 992 }
 993
 994 static int rsa_ossl_finish(RSA *rsa)
 995 {
 996 #ifndef FIPS_MODE
 997     int i;
 998     RSA_PRIME_INFO *pinfo;
 999
1000     for (i = 0; i < sk_RSA_PRIME_INFO_num(rsa->prime_infos); i++) {
1001         pinfo = sk_RSA_PRIME_INFO_value(rsa->prime_infos, i);
1002         BN_MONT_CTX_free(pinfo->m);
1003     }
1004 #endif
1005
1006     BN_MONT_CTX_free(rsa->_method_mod_n);
1007     BN_MONT_CTX_free(rsa->_method_mod_p);
1008     BN_MONT_CTX_free(rsa->_method_mod_q);
1009     return 1;
1010 }