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         goto err;
  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         goto err;
  98     for (i = 0; i < mdlen; i++)
  99         seed[i] ^= seedmask[i];
 100
 101     OPENSSL_free(dbmask);
 102     return 1;
 103
 104  err:
 105     OPENSSL_free(dbmask);
 106     return 0;
 107 }
 108
 109 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 110                                  const unsigned char *from, int flen, int num,
 111                                  const unsigned char *param, int plen)
 112 {
 113     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 114                                              param, plen, NULL, NULL);
 115 }
 116
 117 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 118                                       const unsigned char *from, int flen,
 119                                       int num, const unsigned char *param,
 120                                       int plen, const EVP_MD *md,
 121                                       const EVP_MD *mgf1md)
 122 {
 123     int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
 124     unsigned int good = 0, found_one_byte, mask;
 125     const unsigned char *maskedseed, *maskeddb;
 126     /*
 127      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 128      * Y || maskedSeed || maskedDB
 129      */
 130     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 131         phash[EVP_MAX_MD_SIZE];
 132     int mdlen;
 133
 134     if (md == NULL)
 135         md = EVP_sha1();
 136     if (mgf1md == NULL)
 137         mgf1md = md;
 138
 139     mdlen = EVP_MD_size(md);
 140
 141     if (tlen <= 0 || flen <= 0)
 142         return -1;
 143     /*
 144      * |num| is the length of the modulus; |flen| is the length of the
 145      * encoded message. Therefore, for any |from| that was obtained by
 146      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 147      * num < 2 * mdlen + 2 must hold for the modulus irrespective of
 148      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 149      * This does not leak any side-channel information.
 150      */
 151     if (num < flen || num < 2 * mdlen + 2) {
 152         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 153                RSA_R_OAEP_DECODING_ERROR);
 154         return -1;
 155     }
 156
 157     dblen = num - mdlen - 1;
 158     db = OPENSSL_malloc(dblen);
 159     if (db == NULL) {
 160         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 161         goto cleanup;
 162     }
 163
 164     em = OPENSSL_malloc(num);
 165     if (em == NULL) {
 166         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 167                ERR_R_MALLOC_FAILURE);
 168         goto cleanup;
 169     }
 170
 171     /*
 172      * Caller is encouraged to pass zero-padded message created with
 173      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 174      * bounds, it's impossible to have an invariant memory access pattern
 175      * in case |from| was not zero-padded in advance.
 176      */
 177     for (from += flen, em += num, i = 0; i < num; i++) {
 178         mask = ~constant_time_is_zero(flen);
 179         flen -= 1 & mask;
 180         from -= 1 & mask;
 181         *--em = *from & mask;
 182     }
 183     from = em;
 184
 185     /*
 186      * The first byte must be zero, however we must not leak if this is
 187      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 188      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 189      */
 190     good = constant_time_is_zero(from[0]);
 191
 192     maskedseed = from + 1;
 193     maskeddb = from + 1 + mdlen;
 194
 195     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 196         goto cleanup;
 197     for (i = 0; i < mdlen; i++)
 198         seed[i] ^= maskedseed[i];
 199
 200     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 201         goto cleanup;
 202     for (i = 0; i < dblen; i++)
 203         db[i] ^= maskeddb[i];
 204
 205     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 206         goto cleanup;
 207
 208     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 209
 210     found_one_byte = 0;
 211     for (i = mdlen; i < dblen; i++) {
 212         /*
 213          * Padding consists of a number of 0-bytes, followed by a 1.
 214          */
 215         unsigned int equals1 = constant_time_eq(db[i], 1);
 216         unsigned int equals0 = constant_time_is_zero(db[i]);
 217         one_index = constant_time_select_int(~found_one_byte & equals1,
 218                                              i, one_index);
 219         found_one_byte |= equals1;
 220         good &= (found_one_byte | equals0);
 221     }
 222
 223     good &= found_one_byte;
 224
 225     /*
 226      * At this point |good| is zero unless the plaintext was valid,
 227      * so plaintext-awareness ensures timing side-channels are no longer a
 228      * concern.
 229      */
 230     msg_index = one_index + 1;
 231     mlen = dblen - msg_index;
 232
 233     /*
 234      * For good measure, do this check in constant tine as well.
 235      */
 236     good &= constant_time_ge(tlen, mlen);
 237
 238     /*
 239      * Even though we can't fake result's length, we can pretend copying
 240      * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |dblen|
 241      * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
 242      * where |mlen'| is "saturated" |mlen| value. Deducing information
 243      * about failure or |mlen| would take attacker's ability to observe
 244      * memory access pattern with byte granularity *as it occurs*. It
 245      * should be noted that failure is indistinguishable from normal
 246      * operation if |tlen| is fixed by protocol.
 247      */
 248     tlen = constant_time_select_int(constant_time_lt(dblen, tlen), dblen, tlen);
 249     msg_index = constant_time_select_int(good, msg_index, dblen - tlen);
 250     mlen = dblen - msg_index;
 251     for (from = db + msg_index, mask = good, i = 0; i < tlen; i++) {
 252         unsigned int equals = constant_time_eq(i, mlen);
 253
 254         from -= dblen & equals; /* if (i == dblen) rewind   */
 255         mask &= mask ^ equals;  /* if (i == dblen) mask = 0 */
 256         to[i] = constant_time_select_8(mask, from[i], to[i]);
 257     }
 258
 259     /*
 260      * To avoid chosen ciphertext attacks, the error message should not
 261      * reveal which kind of decoding error happened.
 262      */
 263     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 264            RSA_R_OAEP_DECODING_ERROR);
 265     err_clear_last_constant_time(1 & good);
 266  cleanup:
 267     OPENSSL_cleanse(seed, sizeof(seed));
 268     OPENSSL_cleanse(db, dblen);
 269     OPENSSL_free(db);
 270     OPENSSL_cleanse(em, num);
 271     OPENSSL_free(em);
 272
 273     return constant_time_select_int(good, mlen, -1);
 274 }
 275
 276 int PKCS1_MGF1(unsigned char *mask, long len,
 277                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 278 {
 279     long i, outlen = 0;
 280     unsigned char cnt[4];
 281     EVP_MD_CTX c;
 282     unsigned char md[EVP_MAX_MD_SIZE];
 283     int mdlen;
 284     int rv = -1;
 285
 286     EVP_MD_CTX_init(&c);
 287     mdlen = EVP_MD_size(dgst);
 288     if (mdlen < 0)
 289         goto err;
 290     for (i = 0; outlen < len; i++) {
 291         cnt[0] = (unsigned char)((i >> 24) & 255);
 292         cnt[1] = (unsigned char)((i >> 16) & 255);
 293         cnt[2] = (unsigned char)((i >> 8)) & 255;
 294         cnt[3] = (unsigned char)(i & 255);
 295         if (!EVP_DigestInit_ex(&c, dgst, NULL)
 296             || !EVP_DigestUpdate(&c, seed, seedlen)
 297             || !EVP_DigestUpdate(&c, cnt, 4))
 298             goto err;
 299         if (outlen + mdlen <= len) {
 300             if (!EVP_DigestFinal_ex(&c, mask + outlen, NULL))
 301                 goto err;
 302             outlen += mdlen;
 303         } else {
 304             if (!EVP_DigestFinal_ex(&c, md, NULL))
 305                 goto err;
 306             memcpy(mask + outlen, md, len - outlen);
 307             outlen = len;
 308         }
 309     }
 310     rv = 0;
 311  err:
 312     EVP_MD_CTX_cleanup(&c);
 313     return rv;
 314 }
 315
 316 #endif