crypto/rsa/rsa_oaep.c

   1 /*
   2  * Copyright 1999-2021 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 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
  11
  12 /*
  13  * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
  14  * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
  15  * proof for the original OAEP scheme, which EME-OAEP is based on. A new
  16  * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
  17  * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
  18  * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
  19  * for the underlying permutation: "partial-one-wayness" instead of
  20  * one-wayness.  For the RSA function, this is an equivalent notion.
  21  */
  22
  23 /*
  24  * RSA low level APIs are deprecated for public use, but still ok for
  25  * internal use.
  26  */
  27 #include "internal/deprecated.h"
  28
  29 #include "internal/constant_time.h"
  30
  31 #include <stdio.h>
  32 #include "internal/cryptlib.h"
  33 #include <openssl/bn.h>
  34 #include <openssl/evp.h>
  35 #include <openssl/rand.h>
  36 #include <openssl/sha.h>
  37 #include "rsa_local.h"
  38
  39 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
  40                                const unsigned char *from, int flen,
  41                                const unsigned char *param, int plen)
  42 {
  43     return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
  44                                                    param, plen, NULL, NULL);
  45 }
  46
  47 /*
  48  * Perform the padding as per NIST 800-56B 7.2.2.3
  49  *      from (K) is the key material.
  50  *      param (A) is the additional input.
  51  * Step numbers are included here but not in the constant time inverse below
  52  * to avoid complicating an already difficult enough function.
  53  */
  54 int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx,
  55                                             unsigned char *to, int tlen,
  56                                             const unsigned char *from, int flen,
  57                                             const unsigned char *param,
  58                                             int plen, const EVP_MD *md,
  59                                             const EVP_MD *mgf1md)
  60 {
  61     int rv = 0;
  62     int i, emlen = tlen - 1;
  63     unsigned char *db, *seed;
  64     unsigned char *dbmask = NULL;
  65     unsigned char seedmask[EVP_MAX_MD_SIZE];
  66     int mdlen, dbmask_len = 0;
  67
  68     if (md == NULL) {
  69 #ifndef FIPS_MODULE
  70         md = EVP_sha1();
  71 #else
  72         ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
  73         return 0;
  74 #endif
  75     }
  76     if (mgf1md == NULL)
  77         mgf1md = md;
  78
  79 #ifdef FIPS_MODULE
  80     /* XOF are approved as standalone; Shake256 in Ed448; MGF */
  81     if ((EVP_MD_get_flags(md) & EVP_MD_FLAG_XOF) != 0) {
  82         ERR_raise(ERR_LIB_RSA, RSA_R_DIGEST_NOT_ALLOWED);
  83         return 0;
  84     }
  85     if ((EVP_MD_get_flags(mgf1md) & EVP_MD_FLAG_XOF) != 0) {
  86         ERR_raise(ERR_LIB_RSA, RSA_R_MGF1_DIGEST_NOT_ALLOWED);
  87         return 0;
  88     }
  89 #endif
  90
  91     mdlen = EVP_MD_get_size(md);
  92     if (mdlen <= 0) {
  93         ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
  94         return 0;
  95     }
  96
  97     /* step 2b: check KLen > nLen - 2 HLen - 2 */
  98     if (flen > emlen - 2 * mdlen - 1) {
  99         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
 100         return 0;
 101     }
 102
 103     if (emlen < 2 * mdlen + 1) {
 104         ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL);
 105         return 0;
 106     }
 107
 108     /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
 109     to[0] = 0;
 110     seed = to + 1;
 111     db = to + mdlen + 1;
 112
 113     /* step 3a: hash the additional input */
 114     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
 115         goto err;
 116     /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
 117     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
 118     /* step 3c: DB = HA || PS || 00000001 || K */
 119     db[emlen - flen - mdlen - 1] = 0x01;
 120     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
 121     /* step 3d: generate random byte string */
 122     if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0)
 123         goto err;
 124
 125     dbmask_len = emlen - mdlen;
 126     dbmask = OPENSSL_malloc(dbmask_len);
 127     if (dbmask == NULL)
 128         goto err;
 129
 130     /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
 131     if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
 132         goto err;
 133     /* step 3f: maskedDB = DB XOR dbMask */
 134     for (i = 0; i < dbmask_len; i++)
 135         db[i] ^= dbmask[i];
 136
 137     /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
 138     if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
 139         goto err;
 140     /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
 141     for (i = 0; i < mdlen; i++)
 142         seed[i] ^= seedmask[i];
 143     rv = 1;
 144
 145  err:
 146     OPENSSL_cleanse(seedmask, sizeof(seedmask));
 147     OPENSSL_clear_free(dbmask, dbmask_len);
 148     return rv;
 149 }
 150
 151 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 152                                     const unsigned char *from, int flen,
 153                                     const unsigned char *param, int plen,
 154                                     const EVP_MD *md, const EVP_MD *mgf1md)
 155 {
 156     return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
 157                                                    param, plen, md, mgf1md);
 158 }
 159
 160 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 161                                  const unsigned char *from, int flen, int num,
 162                                  const unsigned char *param, int plen)
 163 {
 164     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 165                                              param, plen, NULL, NULL);
 166 }
 167
 168 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 169                                       const unsigned char *from, int flen,
 170                                       int num, const unsigned char *param,
 171                                       int plen, const EVP_MD *md,
 172                                       const EVP_MD *mgf1md)
 173 {
 174     int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
 175     unsigned int good = 0, found_one_byte, mask;
 176     const unsigned char *maskedseed, *maskeddb;
 177     /*
 178      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 179      * Y || maskedSeed || maskedDB
 180      */
 181     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 182         phash[EVP_MAX_MD_SIZE];
 183     int mdlen;
 184
 185     if (md == NULL) {
 186 #ifndef FIPS_MODULE
 187         md = EVP_sha1();
 188 #else
 189         ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
 190         return -1;
 191 #endif
 192     }
 193
 194     if (mgf1md == NULL)
 195         mgf1md = md;
 196
 197 #ifdef FIPS_MODULE
 198     /* XOF are approved as standalone; Shake256 in Ed448; MGF */
 199     if ((EVP_MD_get_flags(md) & EVP_MD_FLAG_XOF) != 0) {
 200         ERR_raise(ERR_LIB_RSA, RSA_R_DIGEST_NOT_ALLOWED);
 201         return -1;
 202     }
 203     if ((EVP_MD_get_flags(mgf1md) & EVP_MD_FLAG_XOF) != 0) {
 204         ERR_raise(ERR_LIB_RSA, RSA_R_MGF1_DIGEST_NOT_ALLOWED);
 205         return -1;
 206     }
 207 #endif
 208
 209     mdlen = EVP_MD_get_size(md);
 210
 211     if (tlen <= 0 || flen <= 0)
 212         return -1;
 213     /*
 214      * |num| is the length of the modulus; |flen| is the length of the
 215      * encoded message. Therefore, for any |from| that was obtained by
 216      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 217      * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
 218      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 219      * This does not leak any side-channel information.
 220      */
 221     if (num < flen || num < 2 * mdlen + 2) {
 222         ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
 223         return -1;
 224     }
 225
 226     dblen = num - mdlen - 1;
 227     db = OPENSSL_malloc(dblen);
 228     if (db == NULL)
 229         goto cleanup;
 230
 231     em = OPENSSL_malloc(num);
 232     if (em == NULL)
 233         goto cleanup;
 234
 235     /*
 236      * Caller is encouraged to pass zero-padded message created with
 237      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 238      * bounds, it's impossible to have an invariant memory access pattern
 239      * in case |from| was not zero-padded in advance.
 240      */
 241     for (from += flen, em += num, i = 0; i < num; i++) {
 242         mask = ~constant_time_is_zero(flen);
 243         flen -= 1 & mask;
 244         from -= 1 & mask;
 245         *--em = *from & mask;
 246     }
 247
 248     /*
 249      * The first byte must be zero, however we must not leak if this is
 250      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 251      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 252      */
 253     good = constant_time_is_zero(em[0]);
 254
 255     maskedseed = em + 1;
 256     maskeddb = em + 1 + mdlen;
 257
 258     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 259         goto cleanup;
 260     for (i = 0; i < mdlen; i++)
 261         seed[i] ^= maskedseed[i];
 262
 263     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 264         goto cleanup;
 265     for (i = 0; i < dblen; i++)
 266         db[i] ^= maskeddb[i];
 267
 268     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 269         goto cleanup;
 270
 271     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 272
 273     found_one_byte = 0;
 274     for (i = mdlen; i < dblen; i++) {
 275         /*
 276          * Padding consists of a number of 0-bytes, followed by a 1.
 277          */
 278         unsigned int equals1 = constant_time_eq(db[i], 1);
 279         unsigned int equals0 = constant_time_is_zero(db[i]);
 280         one_index = constant_time_select_int(~found_one_byte & equals1,
 281                                              i, one_index);
 282         found_one_byte |= equals1;
 283         good &= (found_one_byte | equals0);
 284     }
 285
 286     good &= found_one_byte;
 287
 288     /*
 289      * At this point |good| is zero unless the plaintext was valid,
 290      * so plaintext-awareness ensures timing side-channels are no longer a
 291      * concern.
 292      */
 293     msg_index = one_index + 1;
 294     mlen = dblen - msg_index;
 295
 296     /*
 297      * For good measure, do this check in constant time as well.
 298      */
 299     good &= constant_time_ge(tlen, mlen);
 300
 301     /*
 302      * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
 303      * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
 304      * Otherwise leave |to| unchanged.
 305      * Copy the memory back in a way that does not reveal the size of
 306      * the data being copied via a timing side channel. This requires copying
 307      * parts of the buffer multiple times based on the bits set in the real
 308      * length. Clear bits do a non-copy with identical access pattern.
 309      * The loop below has overall complexity of O(N*log(N)).
 310      */
 311     tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
 312                                     dblen - mdlen - 1, tlen);
 313     for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
 314         mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
 315         for (i = mdlen + 1; i < dblen - msg_index; i++)
 316             db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
 317     }
 318     for (i = 0; i < tlen; i++) {
 319         mask = good & constant_time_lt(i, mlen);
 320         to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
 321     }
 322
 323 #ifndef FIPS_MODULE
 324     /*
 325      * To avoid chosen ciphertext attacks, the error message should not
 326      * reveal which kind of decoding error happened.
 327      *
 328      * This trick doesn't work in the FIPS provider because libcrypto manages
 329      * the error stack. Instead we opt not to put an error on the stack at all
 330      * in case of padding failure in the FIPS provider.
 331      */
 332     ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
 333     err_clear_last_constant_time(1 & good);
 334 #endif
 335  cleanup:
 336     OPENSSL_cleanse(seed, sizeof(seed));
 337     OPENSSL_clear_free(db, dblen);
 338     OPENSSL_clear_free(em, num);
 339
 340     return constant_time_select_int(good, mlen, -1);
 341 }
 342
 343 /*
 344  * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
 345  * The variables are named differently to NIST:
 346  *      mask (T) and len (maskLen)are the returned mask.
 347  *      seed (mgfSeed).
 348  * The range checking steps inm the process are performed outside.
 349  */
 350 int PKCS1_MGF1(unsigned char *mask, long len,
 351                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 352 {
 353     long i, outlen = 0;
 354     unsigned char cnt[4];
 355     EVP_MD_CTX *c = EVP_MD_CTX_new();
 356     unsigned char md[EVP_MAX_MD_SIZE];
 357     int mdlen;
 358     int rv = -1;
 359
 360     if (c == NULL)
 361         goto err;
 362     mdlen = EVP_MD_get_size(dgst);
 363     if (mdlen < 0)
 364         goto err;
 365     /* step 4 */
 366     for (i = 0; outlen < len; i++) {
 367         /* step 4a: D = I2BS(counter, 4) */
 368         cnt[0] = (unsigned char)((i >> 24) & 255);
 369         cnt[1] = (unsigned char)((i >> 16) & 255);
 370         cnt[2] = (unsigned char)((i >> 8)) & 255;
 371         cnt[3] = (unsigned char)(i & 255);
 372         /* step 4b: T =T || hash(mgfSeed || D) */
 373         if (!EVP_DigestInit_ex(c, dgst, NULL)
 374             || !EVP_DigestUpdate(c, seed, seedlen)
 375             || !EVP_DigestUpdate(c, cnt, 4))
 376             goto err;
 377         if (outlen + mdlen <= len) {
 378             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 379                 goto err;
 380             outlen += mdlen;
 381         } else {
 382             if (!EVP_DigestFinal_ex(c, md, NULL))
 383                 goto err;
 384             memcpy(mask + outlen, md, len - outlen);
 385             outlen = len;
 386         }
 387     }
 388     rv = 0;
 389  err:
 390     OPENSSL_cleanse(md, sizeof(md));
 391     EVP_MD_CTX_free(c);
 392     return rv;
 393 }