crypto/rsa/rsa_oaep.c

   1 /* crypto/rsa/rsa_oaep.c */
   2 /* Written by Ulf Moeller. This software is distributed on an "AS IS"
   3    basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. */
   4
   5 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
   6
   7 /* See Victor Shoup, "OAEP reconsidered," Nov. 2000,
   8  * <URL: http://www.shoup.net/papers/oaep.ps.Z>
   9  * for problems with the security proof for the
  10  * original OAEP scheme, which EME-OAEP is based on.
  11  *
  12  * A new proof can be found in E. Fujisaki, T. Okamoto,
  13  * D. Pointcheval, J. Stern, "RSA-OEAP is Still Alive!",
  14  * Dec. 2000, <URL: http://eprint.iacr.org/2000/061/>.
  15  * The new proof has stronger requirements for the
  16  * underlying permutation: "partial-one-wayness" instead
  17  * of one-wayness.  For the RSA function, this is
  18  * an equivalent notion.
  19  */
  20
  21 #include "constant_time_locl.h"
  22
  23 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
  24 #include <stdio.h>
  25 #include "cryptlib.h"
  26 #include <openssl/bn.h>
  27 #include <openssl/rsa.h>
  28 #include <openssl/evp.h>
  29 #include <openssl/rand.h>
  30 #include <openssl/sha.h>
  31
  32 static int MGF1(unsigned char *mask, long len,
  33         const unsigned char *seed, long seedlen);
  34
  35 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
  36         const unsigned char *from, int flen,
  37         const unsigned char *param, int plen)
  38         {
  39         int i, emlen = tlen - 1;
  40         unsigned char *db, *seed;
  41         unsigned char *dbmask, seedmask[SHA_DIGEST_LENGTH];
  42
  43         if (flen > emlen - 2 * SHA_DIGEST_LENGTH - 1)
  44                 {
  45                 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP,
  46                    RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  47                 return 0;
  48                 }
  49
  50         if (emlen < 2 * SHA_DIGEST_LENGTH + 1)
  51                 {
  52                 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, RSA_R_KEY_SIZE_TOO_SMALL);
  53                 return 0;
  54                 }
  55
  56         to[0] = 0;
  57         seed = to + 1;
  58         db = to + SHA_DIGEST_LENGTH + 1;
  59
  60         if (!EVP_Digest((void *)param, plen, db, NULL, EVP_sha1(), NULL))
  61                 return 0;
  62         memset(db + SHA_DIGEST_LENGTH, 0,
  63                 emlen - flen - 2 * SHA_DIGEST_LENGTH - 1);
  64         db[emlen - flen - SHA_DIGEST_LENGTH - 1] = 0x01;
  65         memcpy(db + emlen - flen - SHA_DIGEST_LENGTH, from, (unsigned int) flen);
  66         if (RAND_bytes(seed, SHA_DIGEST_LENGTH) <= 0)
  67                 return 0;
  68 #ifdef PKCS_TESTVECT
  69         memcpy(seed,
  70            "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
  71            20);
  72 #endif
  73
  74         dbmask = OPENSSL_malloc(emlen - SHA_DIGEST_LENGTH);
  75         if (dbmask == NULL)
  76                 {
  77                 RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
  78                 return 0;
  79                 }
  80
  81         if (MGF1(dbmask, emlen - SHA_DIGEST_LENGTH, seed, SHA_DIGEST_LENGTH) < 0)
  82                 return 0;
  83         for (i = 0; i < emlen - SHA_DIGEST_LENGTH; i++)
  84                 db[i] ^= dbmask[i];
  85
  86         if (MGF1(seedmask, SHA_DIGEST_LENGTH, db, emlen - SHA_DIGEST_LENGTH) < 0)
  87                 return 0;
  88         for (i = 0; i < SHA_DIGEST_LENGTH; i++)
  89                 seed[i] ^= seedmask[i];
  90
  91         OPENSSL_free(dbmask);
  92         return 1;
  93         }
  94
  95 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
  96         const unsigned char *from, int flen, int num,
  97         const unsigned char *param, int plen)
  98         {
  99         int i, dblen, mlen = -1, one_index = 0, msg_index;
 100         unsigned int good, found_one_byte;
 101         const unsigned char *maskedseed, *maskeddb;
 102         /* |em| is the encoded message, zero-padded to exactly |num| bytes:
 103          * em = Y || maskedSeed || maskedDB */
 104         unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 105                 phash[EVP_MAX_MD_SIZE];
 106
 107         if (tlen <= 0 || flen <= 0)
 108                 return -1;
 109
 110         /*
 111          * |num| is the length of the modulus; |flen| is the length of the
 112          * encoded message. Therefore, for any |from| that was obtained by
 113          * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 114          * num < 2 * SHA_DIGEST_LENGTH + 2 must hold for the modulus
 115          * irrespective of the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 116          * This does not leak any side-channel information.
 117          */
 118         if (num < flen || num < 2 * SHA_DIGEST_LENGTH + 2)
 119                 goto decoding_err;
 120
 121         dblen = num - SHA_DIGEST_LENGTH - 1;
 122         db = OPENSSL_malloc(dblen);
 123         em = OPENSSL_malloc(num);
 124         if (db == NULL || em == NULL)
 125                 {
 126                 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, ERR_R_MALLOC_FAILURE);
 127                 goto cleanup;
 128                 }
 129
 130         /*
 131          * Always do this zero-padding copy (even when num == flen) to avoid
 132          * leaking that information. The copy still leaks some side-channel
 133          * information, but it's impossible to have a fixed  memory access
 134          * pattern since we can't read out of the bounds of |from|.
 135          *
 136          * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
 137          */
 138         memset(em, 0, num);
 139         memcpy(em + num - flen, from, flen);
 140
 141         /*
 142          * The first byte must be zero, however we must not leak if this is
 143          * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 144          * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 145          */
 146         good = constant_time_is_zero(em[0]);
 147
 148         maskedseed = em + 1;
 149         maskeddb = em + 1 + SHA_DIGEST_LENGTH;
 150
 151         if (MGF1(seed, SHA_DIGEST_LENGTH, maskeddb, dblen))
 152                 goto cleanup;
 153         for (i = 0; i < SHA_DIGEST_LENGTH; i++)
 154                 seed[i] ^= maskedseed[i];
 155
 156         if (MGF1(db, dblen, seed, SHA_DIGEST_LENGTH))
 157                 goto cleanup;
 158         for (i = 0; i < dblen; i++)
 159                 db[i] ^= maskeddb[i];
 160
 161         if (!EVP_Digest((void *)param, plen, phash, NULL, EVP_sha1(), NULL))
 162                 goto cleanup;
 163
 164         good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, SHA_DIGEST_LENGTH));
 165
 166         found_one_byte = 0;
 167         for (i = SHA_DIGEST_LENGTH; i < dblen; i++)
 168                 {
 169                 /* Padding consists of a number of 0-bytes, followed by a 1. */
 170                 unsigned int equals1 = constant_time_eq(db[i], 1);
 171                 unsigned int equals0 = constant_time_is_zero(db[i]);
 172                 one_index = constant_time_select_int(~found_one_byte & equals1,
 173                         i, one_index);
 174                 found_one_byte |= equals1;
 175                 good &= (found_one_byte | equals0);
 176                 }
 177
 178         good &= found_one_byte;
 179
 180         /*
 181          * At this point |good| is zero unless the plaintext was valid,
 182          * so plaintext-awareness ensures timing side-channels are no longer a
 183          * concern.
 184          */
 185         if (!good)
 186                 goto decoding_err;
 187
 188         msg_index = one_index + 1;
 189         mlen = dblen - msg_index;
 190
 191         if (tlen < mlen)
 192                 {
 193                 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_DATA_TOO_LARGE);
 194                 mlen = -1;
 195                 }
 196         else
 197                 {
 198                 memcpy(to, db + msg_index, mlen);
 199                 goto cleanup;
 200                 }
 201
 202 decoding_err:
 203         /* To avoid chosen ciphertext attacks, the error message should not reveal
 204          * which kind of decoding error happened. */
 205         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP, RSA_R_OAEP_DECODING_ERROR);
 206 cleanup:
 207         if (db != NULL) OPENSSL_free(db);
 208         if (em != NULL) OPENSSL_free(em);
 209         return mlen;
 210         }
 211
 212 int PKCS1_MGF1(unsigned char *mask, long len,
 213         const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 214         {
 215         long i, outlen = 0;
 216         unsigned char cnt[4];
 217         EVP_MD_CTX c;
 218         unsigned char md[EVP_MAX_MD_SIZE];
 219         int mdlen;
 220         int rv = -1;
 221
 222         EVP_MD_CTX_init(&c);
 223         mdlen = EVP_MD_size(dgst);
 224         if (mdlen < 0)
 225                 goto err;
 226         for (i = 0; outlen < len; i++)
 227                 {
 228                 cnt[0] = (unsigned char)((i >> 24) & 255);
 229                 cnt[1] = (unsigned char)((i >> 16) & 255);
 230                 cnt[2] = (unsigned char)((i >> 8)) & 255;
 231                 cnt[3] = (unsigned char)(i & 255);
 232                 if (!EVP_DigestInit_ex(&c,dgst, NULL)
 233                         || !EVP_DigestUpdate(&c, seed, seedlen)
 234                         || !EVP_DigestUpdate(&c, cnt, 4))
 235                         goto err;
 236                 if (outlen + mdlen <= len)
 237                         {
 238                         if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
 239                                 goto err;
 240                         outlen += mdlen;
 241                         }
 242                 else
 243                         {
 244                         if (!EVP_DigestFinal_ex(&c, md, NULL))
 245                                 goto err;
 246                         memcpy(mask + outlen, md, len - outlen);
 247                         outlen = len;
 248                         }
 249                 }
 250         rv = 0;
 251         err:
 252         EVP_MD_CTX_cleanup(&c);
 253         return rv;
 254         }
 255
 256 static int MGF1(unsigned char *mask, long len, const unsigned char *seed,
 257                  long seedlen)
 258         {
 259         return PKCS1_MGF1(mask, len, seed, seedlen, EVP_sha1());
 260         }
 261 #endif