crypto/rsa/rsa_oaep.c

   1 /*
   2  * Copyright 1999-2018 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 #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 rv = 0;
  47     int i, emlen = tlen - 1;
  48     unsigned char *db, *seed;
  49     unsigned char *dbmask = NULL;
  50     unsigned char seedmask[EVP_MAX_MD_SIZE];
  51     int mdlen, dbmask_len = 0;
  52
  53     if (md == NULL)
  54         md = EVP_sha1();
  55     if (mgf1md == NULL)
  56         mgf1md = md;
  57
  58     mdlen = EVP_MD_size(md);
  59
  60     if (flen > emlen - 2 * mdlen - 1) {
  61         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  62                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  63         return 0;
  64     }
  65
  66     if (emlen < 2 * mdlen + 1) {
  67         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  68                RSA_R_KEY_SIZE_TOO_SMALL);
  69         return 0;
  70     }
  71
  72     to[0] = 0;
  73     seed = to + 1;
  74     db = to + mdlen + 1;
  75
  76     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
  77         goto err;
  78     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
  79     db[emlen - flen - mdlen - 1] = 0x01;
  80     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
  81     if (RAND_bytes(seed, mdlen) <= 0)
  82         goto err;
  83
  84     dbmask_len = emlen - mdlen;
  85     dbmask = OPENSSL_malloc(dbmask_len);
  86     if (dbmask == NULL) {
  87         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
  88         goto err;
  89     }
  90
  91     if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
  92         goto err;
  93     for (i = 0; i < dbmask_len; i++)
  94         db[i] ^= dbmask[i];
  95
  96     if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
  97         goto err;
  98     for (i = 0; i < mdlen; i++)
  99         seed[i] ^= seedmask[i];
 100     rv = 1;
 101
 102  err:
 103     OPENSSL_cleanse(seedmask, sizeof(seedmask));
 104     OPENSSL_clear_free(dbmask, dbmask_len);
 105     return rv;
 106 }
 107
 108 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 109                                  const unsigned char *from, int flen, int num,
 110                                  const unsigned char *param, int plen)
 111 {
 112     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 113                                              param, plen, NULL, NULL);
 114 }
 115
 116 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 117                                       const unsigned char *from, int flen,
 118                                       int num, const unsigned char *param,
 119                                       int plen, const EVP_MD *md,
 120                                       const EVP_MD *mgf1md)
 121 {
 122     int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
 123     unsigned int good = 0, found_one_byte, mask;
 124     const unsigned char *maskedseed, *maskeddb;
 125     /*
 126      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 127      * Y || maskedSeed || maskedDB
 128      */
 129     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 130         phash[EVP_MAX_MD_SIZE];
 131     int mdlen;
 132
 133     if (md == NULL)
 134         md = EVP_sha1();
 135     if (mgf1md == NULL)
 136         mgf1md = md;
 137
 138     mdlen = EVP_MD_size(md);
 139
 140     if (tlen <= 0 || flen <= 0)
 141         return -1;
 142     /*
 143      * |num| is the length of the modulus; |flen| is the length of the
 144      * encoded message. Therefore, for any |from| that was obtained by
 145      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 146      * num < 2 * mdlen + 2 must hold for the modulus irrespective of
 147      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 148      * This does not leak any side-channel information.
 149      */
 150     if (num < flen || num < 2 * mdlen + 2) {
 151         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 152                RSA_R_OAEP_DECODING_ERROR);
 153         return -1;
 154     }
 155
 156     dblen = num - mdlen - 1;
 157     db = OPENSSL_malloc(dblen);
 158     if (db == NULL) {
 159         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 160         goto cleanup;
 161     }
 162
 163     em = OPENSSL_malloc(num);
 164     if (em == NULL) {
 165         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 166                ERR_R_MALLOC_FAILURE);
 167         goto cleanup;
 168     }
 169
 170     /*
 171      * Caller is encouraged to pass zero-padded message created with
 172      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 173      * bounds, it's impossible to have an invariant memory access pattern
 174      * in case |from| was not zero-padded in advance.
 175      */
 176     for (from += flen, em += num, i = 0; i < num; i++) {
 177         mask = ~constant_time_is_zero(flen);
 178         flen -= 1 & mask;
 179         from -= 1 & mask;
 180         *--em = *from & mask;
 181     }
 182     from = em;
 183
 184     /*
 185      * The first byte must be zero, however we must not leak if this is
 186      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 187      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 188      */
 189     good = constant_time_is_zero(from[0]);
 190
 191     maskedseed = from + 1;
 192     maskeddb = from + 1 + mdlen;
 193
 194     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 195         goto cleanup;
 196     for (i = 0; i < mdlen; i++)
 197         seed[i] ^= maskedseed[i];
 198
 199     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 200         goto cleanup;
 201     for (i = 0; i < dblen; i++)
 202         db[i] ^= maskeddb[i];
 203
 204     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 205         goto cleanup;
 206
 207     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 208
 209     found_one_byte = 0;
 210     for (i = mdlen; i < dblen; i++) {
 211         /*
 212          * Padding consists of a number of 0-bytes, followed by a 1.
 213          */
 214         unsigned int equals1 = constant_time_eq(db[i], 1);
 215         unsigned int equals0 = constant_time_is_zero(db[i]);
 216         one_index = constant_time_select_int(~found_one_byte & equals1,
 217                                              i, one_index);
 218         found_one_byte |= equals1;
 219         good &= (found_one_byte | equals0);
 220     }
 221
 222     good &= found_one_byte;
 223
 224     /*
 225      * At this point |good| is zero unless the plaintext was valid,
 226      * so plaintext-awareness ensures timing side-channels are no longer a
 227      * concern.
 228      */
 229     msg_index = one_index + 1;
 230     mlen = dblen - msg_index;
 231
 232     /*
 233      * For good measure, do this check in constant tine as well.
 234      */
 235     good &= constant_time_ge(tlen, mlen);
 236
 237     /*
 238      * Even though we can't fake result's length, we can pretend copying
 239      * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |dblen|
 240      * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
 241      * where |mlen'| is "saturated" |mlen| value. Deducing information
 242      * about failure or |mlen| would take attacker's ability to observe
 243      * memory access pattern with byte granularity *as it occurs*. It
 244      * should be noted that failure is indistinguishable from normal
 245      * operation if |tlen| is fixed by protocol.
 246      */
 247     tlen = constant_time_select_int(constant_time_lt(dblen, tlen), dblen, tlen);
 248     msg_index = constant_time_select_int(good, msg_index, dblen - tlen);
 249     mlen = dblen - msg_index;
 250     for (from = db + msg_index, mask = good, i = 0; i < tlen; i++) {
 251         unsigned int equals = constant_time_eq(i, mlen);
 252
 253         from -= dblen & equals; /* if (i == dblen) rewind   */
 254         mask &= mask ^ equals;  /* if (i == dblen) mask = 0 */
 255         to[i] = constant_time_select_8(mask, from[i], to[i]);
 256     }
 257
 258     /*
 259      * To avoid chosen ciphertext attacks, the error message should not
 260      * reveal which kind of decoding error happened.
 261      */
 262     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 263            RSA_R_OAEP_DECODING_ERROR);
 264     err_clear_last_constant_time(1 & good);
 265  cleanup:
 266     OPENSSL_cleanse(seed, sizeof(seed));
 267     OPENSSL_clear_free(db, dblen);
 268     OPENSSL_clear_free(em, num);
 269
 270     return constant_time_select_int(good, mlen, -1);
 271 }
 272
 273 int PKCS1_MGF1(unsigned char *mask, long len,
 274                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 275 {
 276     long i, outlen = 0;
 277     unsigned char cnt[4];
 278     EVP_MD_CTX *c = EVP_MD_CTX_new();
 279     unsigned char md[EVP_MAX_MD_SIZE];
 280     int mdlen;
 281     int rv = -1;
 282
 283     if (c == NULL)
 284         goto err;
 285     mdlen = EVP_MD_size(dgst);
 286     if (mdlen < 0)
 287         goto err;
 288     for (i = 0; outlen < len; i++) {
 289         cnt[0] = (unsigned char)((i >> 24) & 255);
 290         cnt[1] = (unsigned char)((i >> 16) & 255);
 291         cnt[2] = (unsigned char)((i >> 8)) & 255;
 292         cnt[3] = (unsigned char)(i & 255);
 293         if (!EVP_DigestInit_ex(c, dgst, NULL)
 294             || !EVP_DigestUpdate(c, seed, seedlen)
 295             || !EVP_DigestUpdate(c, cnt, 4))
 296             goto err;
 297         if (outlen + mdlen <= len) {
 298             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 299                 goto err;
 300             outlen += mdlen;
 301         } else {
 302             if (!EVP_DigestFinal_ex(c, md, NULL))
 303                 goto err;
 304             memcpy(mask + outlen, md, len - outlen);
 305             outlen = len;
 306         }
 307     }
 308     rv = 0;
 309  err:
 310     OPENSSL_cleanse(md, sizeof(md));
 311     EVP_MD_CTX_free(c);
 312     return rv;
 313 }