crypto/rsa/rsa_oaep.c

   1 /*
   2  * Copyright 1999-2016 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   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
   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 #include "internal/constant_time_locl.h"
  24
  25 #include <stdio.h>
  26 #include "internal/cryptlib.h"
  27 #include <openssl/bn.h>
  28 #include <openssl/evp.h>
  29 #include <openssl/rand.h>
  30 #include <openssl/sha.h>
  31 #include "rsa_locl.h"
  32
  33 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
  34                                const unsigned char *from, int flen,
  35                                const unsigned char *param, int plen)
  36 {
  37     return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
  38                                            param, plen, NULL, NULL);
  39 }
  40
  41 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
  42                                     const unsigned char *from, int flen,
  43                                     const unsigned char *param, int plen,
  44                                     const EVP_MD *md, const EVP_MD *mgf1md)
  45 {
  46     int i, emlen = tlen - 1;
  47     unsigned char *db, *seed;
  48     unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
  49     int mdlen;
  50
  51     if (md == NULL)
  52         md = EVP_sha1();
  53     if (mgf1md == NULL)
  54         mgf1md = md;
  55
  56     mdlen = EVP_MD_size(md);
  57
  58     if (flen > emlen - 2 * mdlen - 1) {
  59         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  60                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  61         return 0;
  62     }
  63
  64     if (emlen < 2 * mdlen + 1) {
  65         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  66                RSA_R_KEY_SIZE_TOO_SMALL);
  67         return 0;
  68     }
  69
  70     to[0] = 0;
  71     seed = to + 1;
  72     db = to + mdlen + 1;
  73
  74     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
  75         return 0;
  76     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
  77     db[emlen - flen - mdlen - 1] = 0x01;
  78     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
  79     if (RAND_bytes(seed, mdlen) <= 0)
  80         return 0;
  81 #ifdef PKCS_TESTVECT
  82     memcpy(seed,
  83            "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
  84            20);
  85 #endif
  86
  87     dbmask = OPENSSL_malloc(emlen - mdlen);
  88     if (dbmask == NULL) {
  89         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
  90         return 0;
  91     }
  92
  93     if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
  94         return 0;
  95     for (i = 0; i < emlen - mdlen; i++)
  96         db[i] ^= dbmask[i];
  97
  98     if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
  99         return 0;
 100     for (i = 0; i < mdlen; i++)
 101         seed[i] ^= seedmask[i];
 102
 103     OPENSSL_free(dbmask);
 104     return 1;
 105 }
 106
 107 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 108                                  const unsigned char *from, int flen, int num,
 109                                  const unsigned char *param, int plen)
 110 {
 111     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 112                                              param, plen, NULL, NULL);
 113 }
 114
 115 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 116                                       const unsigned char *from, int flen,
 117                                       int num, const unsigned char *param,
 118                                       int plen, const EVP_MD *md,
 119                                       const EVP_MD *mgf1md)
 120 {
 121     int i, dblen, mlen = -1, one_index = 0, msg_index;
 122     unsigned int good, found_one_byte;
 123     const unsigned char *maskedseed, *maskeddb;
 124     /*
 125      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 126      * Y || maskedSeed || maskedDB
 127      */
 128     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 129         phash[EVP_MAX_MD_SIZE];
 130     int mdlen;
 131
 132     if (md == NULL)
 133         md = EVP_sha1();
 134     if (mgf1md == NULL)
 135         mgf1md = md;
 136
 137     mdlen = EVP_MD_size(md);
 138
 139     if (tlen <= 0 || flen <= 0)
 140         return -1;
 141     /*
 142      * |num| is the length of the modulus; |flen| is the length of the
 143      * encoded message. Therefore, for any |from| that was obtained by
 144      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 145      * num < 2 * mdlen + 2 must hold for the modulus irrespective of
 146      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 147      * This does not leak any side-channel information.
 148      */
 149     if (num < flen || num < 2 * mdlen + 2)
 150         goto decoding_err;
 151
 152     dblen = num - mdlen - 1;
 153     db = OPENSSL_malloc(dblen);
 154     em = OPENSSL_malloc(num);
 155     if (db == NULL || em == NULL) {
 156         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 157         goto cleanup;
 158     }
 159
 160     /*
 161      * Always do this zero-padding copy (even when num == flen) to avoid
 162      * leaking that information. The copy still leaks some side-channel
 163      * information, but it's impossible to have a fixed  memory access
 164      * pattern since we can't read out of the bounds of |from|.
 165      *
 166      * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
 167      */
 168     memset(em, 0, num);
 169     memcpy(em + num - flen, from, flen);
 170
 171     /*
 172      * The first byte must be zero, however we must not leak if this is
 173      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 174      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 175      */
 176     good = constant_time_is_zero(em[0]);
 177
 178     maskedseed = em + 1;
 179     maskeddb = em + 1 + mdlen;
 180
 181     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 182         goto cleanup;
 183     for (i = 0; i < mdlen; i++)
 184         seed[i] ^= maskedseed[i];
 185
 186     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 187         goto cleanup;
 188     for (i = 0; i < dblen; i++)
 189         db[i] ^= maskeddb[i];
 190
 191     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 192         goto cleanup;
 193
 194     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 195
 196     found_one_byte = 0;
 197     for (i = mdlen; i < dblen; i++) {
 198         /*
 199          * Padding consists of a number of 0-bytes, followed by a 1.
 200          */
 201         unsigned int equals1 = constant_time_eq(db[i], 1);
 202         unsigned int equals0 = constant_time_is_zero(db[i]);
 203         one_index = constant_time_select_int(~found_one_byte & equals1,
 204                                              i, one_index);
 205         found_one_byte |= equals1;
 206         good &= (found_one_byte | equals0);
 207     }
 208
 209     good &= found_one_byte;
 210
 211     /*
 212      * At this point |good| is zero unless the plaintext was valid,
 213      * so plaintext-awareness ensures timing side-channels are no longer a
 214      * concern.
 215      */
 216     if (!good)
 217         goto decoding_err;
 218
 219     msg_index = one_index + 1;
 220     mlen = dblen - msg_index;
 221
 222     if (tlen < mlen) {
 223         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
 224         mlen = -1;
 225     } else {
 226         memcpy(to, db + msg_index, mlen);
 227         goto cleanup;
 228     }
 229
 230  decoding_err:
 231     /*
 232      * To avoid chosen ciphertext attacks, the error message should not
 233      * reveal which kind of decoding error happened.
 234      */
 235     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 236            RSA_R_OAEP_DECODING_ERROR);
 237  cleanup:
 238     OPENSSL_free(db);
 239     OPENSSL_free(em);
 240     return mlen;
 241 }
 242
 243 int PKCS1_MGF1(unsigned char *mask, long len,
 244                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 245 {
 246     long i, outlen = 0;
 247     unsigned char cnt[4];
 248     EVP_MD_CTX *c = EVP_MD_CTX_new();
 249     unsigned char md[EVP_MAX_MD_SIZE];
 250     int mdlen;
 251     int rv = -1;
 252
 253     if (c == NULL)
 254         goto err;
 255     mdlen = EVP_MD_size(dgst);
 256     if (mdlen < 0)
 257         goto err;
 258     for (i = 0; outlen < len; i++) {
 259         cnt[0] = (unsigned char)((i >> 24) & 255);
 260         cnt[1] = (unsigned char)((i >> 16) & 255);
 261         cnt[2] = (unsigned char)((i >> 8)) & 255;
 262         cnt[3] = (unsigned char)(i & 255);
 263         if (!EVP_DigestInit_ex(c, dgst, NULL)
 264             || !EVP_DigestUpdate(c, seed, seedlen)
 265             || !EVP_DigestUpdate(c, cnt, 4))
 266             goto err;
 267         if (outlen + mdlen <= len) {
 268             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 269                 goto err;
 270             outlen += mdlen;
 271         } else {
 272             if (!EVP_DigestFinal_ex(c, md, NULL))
 273                 goto err;
 274             memcpy(mask + outlen, md, len - outlen);
 275             outlen = len;
 276         }
 277     }
 278     rv = 0;
 279  err:
 280     EVP_MD_CTX_free(c);
 281     return rv;
 282 }