crypto/rsa/rsa_oaep.c

   1 /*
   2  * Copyright 1999-2019 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.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_local.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 /*
  42  * Perform ihe padding as per NIST 800-56B 7.2.2.3
  43  *      from (K) is the key material.
  44  *      param (A) is the additional input.
  45  * Step numbers are included here but not in the constant time inverse below
  46  * to avoid complicating an already difficult enough function.
  47  */
  48 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
  49                                     const unsigned char *from, int flen,
  50                                     const unsigned char *param, int plen,
  51                                     const EVP_MD *md, const EVP_MD *mgf1md)
  52 {
  53     int rv = 0;
  54     int i, emlen = tlen - 1;
  55     unsigned char *db, *seed;
  56     unsigned char *dbmask = NULL;
  57     unsigned char seedmask[EVP_MAX_MD_SIZE];
  58     int mdlen, dbmask_len = 0;
  59
  60     if (md == NULL)
  61         md = EVP_sha1();
  62     if (mgf1md == NULL)
  63         mgf1md = md;
  64
  65     mdlen = EVP_MD_size(md);
  66
  67     /* step 2b: check KLen > nLen - 2 HLen - 2 */
  68     if (flen > emlen - 2 * mdlen - 1) {
  69         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  70                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  71         return 0;
  72     }
  73
  74     if (emlen < 2 * mdlen + 1) {
  75         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
  76                RSA_R_KEY_SIZE_TOO_SMALL);
  77         return 0;
  78     }
  79
  80     /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
  81     to[0] = 0;
  82     seed = to + 1;
  83     db = to + mdlen + 1;
  84
  85     /* step 3a: hash the additional input */
  86     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
  87         goto err;
  88     /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
  89     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
  90     /* step 3c: DB = HA || PS || 00000001 || K */
  91     db[emlen - flen - mdlen - 1] = 0x01;
  92     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
  93     /* step 3d: generate random byte string */
  94     if (RAND_bytes(seed, mdlen) <= 0)
  95         goto err;
  96
  97     dbmask_len = emlen - mdlen;
  98     dbmask = OPENSSL_malloc(dbmask_len);
  99     if (dbmask == NULL) {
 100         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 101         goto err;
 102     }
 103
 104     /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
 105     if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
 106         goto err;
 107     /* step 3f: maskedDB = DB XOR dbMask */
 108     for (i = 0; i < dbmask_len; i++)
 109         db[i] ^= dbmask[i];
 110
 111     /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
 112     if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
 113         goto err;
 114     /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
 115     for (i = 0; i < mdlen; i++)
 116         seed[i] ^= seedmask[i];
 117     rv = 1;
 118
 119  err:
 120     OPENSSL_cleanse(seedmask, sizeof(seedmask));
 121     OPENSSL_clear_free(dbmask, dbmask_len);
 122     return rv;
 123 }
 124
 125 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 126                                  const unsigned char *from, int flen, int num,
 127                                  const unsigned char *param, int plen)
 128 {
 129     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 130                                              param, plen, NULL, NULL);
 131 }
 132
 133 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 134                                       const unsigned char *from, int flen,
 135                                       int num, const unsigned char *param,
 136                                       int plen, const EVP_MD *md,
 137                                       const EVP_MD *mgf1md)
 138 {
 139     int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
 140     unsigned int good = 0, found_one_byte, mask;
 141     const unsigned char *maskedseed, *maskeddb;
 142     /*
 143      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 144      * Y || maskedSeed || maskedDB
 145      */
 146     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 147         phash[EVP_MAX_MD_SIZE];
 148     int mdlen;
 149
 150     if (md == NULL)
 151         md = EVP_sha1();
 152     if (mgf1md == NULL)
 153         mgf1md = md;
 154
 155     mdlen = EVP_MD_size(md);
 156
 157     if (tlen <= 0 || flen <= 0)
 158         return -1;
 159     /*
 160      * |num| is the length of the modulus; |flen| is the length of the
 161      * encoded message. Therefore, for any |from| that was obtained by
 162      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 163      * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
 164      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 165      * This does not leak any side-channel information.
 166      */
 167     if (num < flen || num < 2 * mdlen + 2) {
 168         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 169                RSA_R_OAEP_DECODING_ERROR);
 170         return -1;
 171     }
 172
 173     dblen = num - mdlen - 1;
 174     db = OPENSSL_malloc(dblen);
 175     if (db == NULL) {
 176         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 177         goto cleanup;
 178     }
 179
 180     em = OPENSSL_malloc(num);
 181     if (em == NULL) {
 182         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 183                ERR_R_MALLOC_FAILURE);
 184         goto cleanup;
 185     }
 186
 187     /*
 188      * Caller is encouraged to pass zero-padded message created with
 189      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 190      * bounds, it's impossible to have an invariant memory access pattern
 191      * in case |from| was not zero-padded in advance.
 192      */
 193     for (from += flen, em += num, i = 0; i < num; i++) {
 194         mask = ~constant_time_is_zero(flen);
 195         flen -= 1 & mask;
 196         from -= 1 & mask;
 197         *--em = *from & mask;
 198     }
 199
 200     /*
 201      * The first byte must be zero, however we must not leak if this is
 202      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 203      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 204      */
 205     good = constant_time_is_zero(em[0]);
 206
 207     maskedseed = em + 1;
 208     maskeddb = em + 1 + mdlen;
 209
 210     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 211         goto cleanup;
 212     for (i = 0; i < mdlen; i++)
 213         seed[i] ^= maskedseed[i];
 214
 215     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 216         goto cleanup;
 217     for (i = 0; i < dblen; i++)
 218         db[i] ^= maskeddb[i];
 219
 220     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 221         goto cleanup;
 222
 223     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 224
 225     found_one_byte = 0;
 226     for (i = mdlen; i < dblen; i++) {
 227         /*
 228          * Padding consists of a number of 0-bytes, followed by a 1.
 229          */
 230         unsigned int equals1 = constant_time_eq(db[i], 1);
 231         unsigned int equals0 = constant_time_is_zero(db[i]);
 232         one_index = constant_time_select_int(~found_one_byte & equals1,
 233                                              i, one_index);
 234         found_one_byte |= equals1;
 235         good &= (found_one_byte | equals0);
 236     }
 237
 238     good &= found_one_byte;
 239
 240     /*
 241      * At this point |good| is zero unless the plaintext was valid,
 242      * so plaintext-awareness ensures timing side-channels are no longer a
 243      * concern.
 244      */
 245     msg_index = one_index + 1;
 246     mlen = dblen - msg_index;
 247
 248     /*
 249      * For good measure, do this check in constant time as well.
 250      */
 251     good &= constant_time_ge(tlen, mlen);
 252
 253     /*
 254      * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
 255      * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
 256      * Otherwise leave |to| unchanged.
 257      * Copy the memory back in a way that does not reveal the size of
 258      * the data being copied via a timing side channel. This requires copying
 259      * parts of the buffer multiple times based on the bits set in the real
 260      * length. Clear bits do a non-copy with identical access pattern.
 261      * The loop below has overall complexity of O(N*log(N)).
 262      */
 263     tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
 264                                     dblen - mdlen - 1, tlen);
 265     for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
 266         mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
 267         for (i = mdlen + 1; i < dblen - msg_index; i++)
 268             db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
 269     }
 270     for (i = 0; i < tlen; i++) {
 271         mask = good & constant_time_lt(i, mlen);
 272         to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
 273     }
 274
 275     /*
 276      * To avoid chosen ciphertext attacks, the error message should not
 277      * reveal which kind of decoding error happened.
 278      */
 279     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 280            RSA_R_OAEP_DECODING_ERROR);
 281     err_clear_last_constant_time(1 & good);
 282  cleanup:
 283     OPENSSL_cleanse(seed, sizeof(seed));
 284     OPENSSL_clear_free(db, dblen);
 285     OPENSSL_clear_free(em, num);
 286
 287     return constant_time_select_int(good, mlen, -1);
 288 }
 289
 290 /*
 291  * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
 292  * The variables are named differently to NIST:
 293  *      mask (T) and len (maskLen)are the returned mask.
 294  *      seed (mgfSeed).
 295  * The range checking steps inm the process are performed outside.
 296  */
 297 int PKCS1_MGF1(unsigned char *mask, long len,
 298                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 299 {
 300     long i, outlen = 0;
 301     unsigned char cnt[4];
 302     EVP_MD_CTX *c = EVP_MD_CTX_new();
 303     unsigned char md[EVP_MAX_MD_SIZE];
 304     int mdlen;
 305     int rv = -1;
 306
 307     if (c == NULL)
 308         goto err;
 309     mdlen = EVP_MD_size(dgst);
 310     if (mdlen < 0)
 311         goto err;
 312     /* step 4 */
 313     for (i = 0; outlen < len; i++) {
 314         /* step 4a: D = I2BS(counter, 4) */
 315         cnt[0] = (unsigned char)((i >> 24) & 255);
 316         cnt[1] = (unsigned char)((i >> 16) & 255);
 317         cnt[2] = (unsigned char)((i >> 8)) & 255;
 318         cnt[3] = (unsigned char)(i & 255);
 319         /* step 4b: T =T || hash(mgfSeed || D) */
 320         if (!EVP_DigestInit_ex(c, dgst, NULL)
 321             || !EVP_DigestUpdate(c, seed, seedlen)
 322             || !EVP_DigestUpdate(c, cnt, 4))
 323             goto err;
 324         if (outlen + mdlen <= len) {
 325             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 326                 goto err;
 327             outlen += mdlen;
 328         } else {
 329             if (!EVP_DigestFinal_ex(c, md, NULL))
 330                 goto err;
 331             memcpy(mask + outlen, md, len - outlen);
 332             outlen = len;
 333         }
 334     }
 335     rv = 0;
 336  err:
 337     OPENSSL_cleanse(md, sizeof(md));
 338     EVP_MD_CTX_free(c);
 339     return rv;
 340 }