crypto/rsa/rsa_oaep.c

   1 /* crypto/rsa/rsa_oaep.c */
   2 /*
   3  * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
   4  * WITHOUT WARRANTY OF ANY KIND, either express or implied.
   5  */
   6
   7 /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
   8
   9 /*
  10  * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
  11  * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
  12  * proof for the original OAEP scheme, which EME-OAEP is based on. A new
  13  * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
  14  * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
  15  * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
  16  * for the underlying permutation: "partial-one-wayness" instead of
  17  * one-wayness.  For the RSA function, this is an equivalent notion.
  18  */
  19
  20 #include "constant_time_locl.h"
  21
  22 #if !defined(OPENSSL_NO_SHA) && !defined(OPENSSL_NO_SHA1)
  23 # include <stdio.h>
  24 # include "cryptlib.h"
  25 # include <openssl/bn.h>
  26 # include <openssl/rsa.h>
  27 # include <openssl/evp.h>
  28 # include <openssl/rand.h>
  29 # include <openssl/sha.h>
  30
  31 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
  32                                const unsigned char *from, int flen,
  33                                const unsigned char *param, int plen)
  34 {
  35     return RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
  36                                            param, plen, NULL, NULL);
  37 }
  38
  39 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
  40                                     const unsigned char *from, int flen,
  41                                     const unsigned char *param, int plen,
  42                                     const EVP_MD *md, const EVP_MD *mgf1md)
  43 {
  44     int i, emlen = tlen - 1;
  45     unsigned char *db, *seed;
  46     unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
  47     int mdlen;
  48
  49     if (md == NULL)
  50         md = EVP_sha1();
  51     if (mgf1md == NULL)
  52         mgf1md = md;
  53
  54     mdlen = EVP_MD_size(md);
  55
  56     if (flen > emlen - 2 * mdlen - 1) {
  57         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  58                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  59         return 0;
  60     }
  61
  62     if (emlen < 2 * mdlen + 1) {
  63         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  64                RSA_R_KEY_SIZE_TOO_SMALL);
  65         return 0;
  66     }
  67
  68     to[0] = 0;
  69     seed = to + 1;
  70     db = to + mdlen + 1;
  71
  72     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
  73         return 0;
  74     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
  75     db[emlen - flen - mdlen - 1] = 0x01;
  76     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
  77     if (RAND_bytes(seed, mdlen) <= 0)
  78         return 0;
  79 # ifdef PKCS_TESTVECT
  80     memcpy(seed,
  81            "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
  82            20);
  83 # endif
  84
  85     dbmask = OPENSSL_malloc(emlen - mdlen);
  86     if (dbmask == NULL) {
  87         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
  88         return 0;
  89     }
  90
  91     if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
  92         return 0;
  93     for (i = 0; i < emlen - mdlen; i++)
  94         db[i] ^= dbmask[i];
  95
  96     if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
  97         return 0;
  98     for (i = 0; i < mdlen; i++)
  99         seed[i] ^= seedmask[i];
 100
 101     OPENSSL_free(dbmask);
 102     return 1;
 103 }
 104
 105 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 106                                  const unsigned char *from, int flen, int num,
 107                                  const unsigned char *param, int plen)
 108 {
 109     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 110                                              param, plen, NULL, NULL);
 111 }
 112
 113 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 114                                       const unsigned char *from, int flen,
 115                                       int num, const unsigned char *param,
 116                                       int plen, const EVP_MD *md,
 117                                       const EVP_MD *mgf1md)
 118 {
 119     int i, dblen, mlen = -1, one_index = 0, msg_index;
 120     unsigned int good, found_one_byte;
 121     const unsigned char *maskedseed, *maskeddb;
 122     /*
 123      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 124      * Y || maskedSeed || maskedDB
 125      */
 126     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 127         phash[EVP_MAX_MD_SIZE];
 128     int mdlen;
 129
 130     if (md == NULL)
 131         md = EVP_sha1();
 132     if (mgf1md == NULL)
 133         mgf1md = md;
 134
 135     mdlen = EVP_MD_size(md);
 136
 137     if (tlen <= 0 || flen <= 0)
 138         return -1;
 139     /*
 140      * |num| is the length of the modulus; |flen| is the length of the
 141      * encoded message. Therefore, for any |from| that was obtained by
 142      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 143      * num < 2 * mdlen + 2 must hold for the modulus irrespective of
 144      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 145      * This does not leak any side-channel information.
 146      */
 147     if (num < flen || num < 2 * mdlen + 2)
 148         goto decoding_err;
 149
 150     dblen = num - mdlen - 1;
 151     db = OPENSSL_malloc(dblen);
 152     em = OPENSSL_malloc(num);
 153     if (db == NULL || em == NULL) {
 154         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 155         goto cleanup;
 156     }
 157
 158     /*
 159      * Always do this zero-padding copy (even when num == flen) to avoid
 160      * leaking that information. The copy still leaks some side-channel
 161      * information, but it's impossible to have a fixed  memory access
 162      * pattern since we can't read out of the bounds of |from|.
 163      *
 164      * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
 165      */
 166     memset(em, 0, num);
 167     memcpy(em + num - flen, from, flen);
 168
 169     /*
 170      * The first byte must be zero, however we must not leak if this is
 171      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 172      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 173      */
 174     good = constant_time_is_zero(em[0]);
 175
 176     maskedseed = em + 1;
 177     maskeddb = em + 1 + mdlen;
 178
 179     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 180         goto cleanup;
 181     for (i = 0; i < mdlen; i++)
 182         seed[i] ^= maskedseed[i];
 183
 184     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 185         goto cleanup;
 186     for (i = 0; i < dblen; i++)
 187         db[i] ^= maskeddb[i];
 188
 189     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 190         goto cleanup;
 191
 192     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 193
 194     found_one_byte = 0;
 195     for (i = mdlen; i < dblen; i++) {
 196         /*
 197          * Padding consists of a number of 0-bytes, followed by a 1.
 198          */
 199         unsigned int equals1 = constant_time_eq(db[i], 1);
 200         unsigned int equals0 = constant_time_is_zero(db[i]);
 201         one_index = constant_time_select_int(~found_one_byte & equals1,
 202                                              i, one_index);
 203         found_one_byte |= equals1;
 204         good &= (found_one_byte | equals0);
 205     }
 206
 207     good &= found_one_byte;
 208
 209     /*
 210      * At this point |good| is zero unless the plaintext was valid,
 211      * so plaintext-awareness ensures timing side-channels are no longer a
 212      * concern.
 213      */
 214     if (!good)
 215         goto decoding_err;
 216
 217     msg_index = one_index + 1;
 218     mlen = dblen - msg_index;
 219
 220     if (tlen < mlen) {
 221         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
 222         mlen = -1;
 223     } else {
 224         memcpy(to, db + msg_index, mlen);
 225         goto cleanup;
 226     }
 227
 228  decoding_err:
 229     /*
 230      * To avoid chosen ciphertext attacks, the error message should not
 231      * reveal which kind of decoding error happened.
 232      */
 233     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 234            RSA_R_OAEP_DECODING_ERROR);
 235  cleanup:
 236     if (db != NULL)
 237         OPENSSL_free(db);
 238     if (em != NULL)
 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;
 249     unsigned char md[EVP_MAX_MD_SIZE];
 250     int mdlen;
 251     int rv = -1;
 252
 253     EVP_MD_CTX_init(&c);
 254     mdlen = M_EVP_MD_size(dgst);
 255     if (mdlen < 0)
 256         goto err;
 257     for (i = 0; outlen < len; i++) {
 258         cnt[0] = (unsigned char)((i >> 24) & 255);
 259         cnt[1] = (unsigned char)((i >> 16) & 255);
 260         cnt[2] = (unsigned char)((i >> 8)) & 255;
 261         cnt[3] = (unsigned char)(i & 255);
 262         if (!EVP_DigestInit_ex(&c, dgst, NULL)
 263             || !EVP_DigestUpdate(&c, seed, seedlen)
 264             || !EVP_DigestUpdate(&c, cnt, 4))
 265             goto err;
 266         if (outlen + mdlen <= len) {
 267             if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
 268                 goto err;
 269             outlen += mdlen;
 270         } else {
 271             if (!EVP_DigestFinal_ex(&c, md, NULL))
 272                 goto err;
 273             memcpy(mask + outlen, md, len - outlen);
 274             outlen = len;
 275         }
 276     }
 277     rv = 0;
 278  err:
 279     EVP_MD_CTX_cleanup(&c);
 280     return rv;
 281 }
 282
 283 #endif