crypto/rsa/rsa_oaep.c

   1 /*
   2  * Copyright 1999-2020 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 /*
  24  * RSA low level APIs are deprecated for public use, but still ok for
  25  * internal use.
  26  */
  27 #include "internal/deprecated.h"
  28
  29 #include "internal/constant_time.h"
  30
  31 #include <stdio.h>
  32 #include "internal/cryptlib.h"
  33 #include <openssl/bn.h>
  34 #include <openssl/evp.h>
  35 #include <openssl/rand.h>
  36 #include <openssl/sha.h>
  37 #include "rsa_local.h"
  38
  39 int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
  40                                const unsigned char *from, int flen,
  41                                const unsigned char *param, int plen)
  42 {
  43     return rsa_padding_add_PKCS1_OAEP_mgf1_with_libctx(NULL, to, tlen, from,
  44                                                        flen, param, plen, NULL,
  45                                                        NULL);
  46 }
  47
  48 /*
  49  * Perform ihe padding as per NIST 800-56B 7.2.2.3
  50  *      from (K) is the key material.
  51  *      param (A) is the additional input.
  52  * Step numbers are included here but not in the constant time inverse below
  53  * to avoid complicating an already difficult enough function.
  54  */
  55 int rsa_padding_add_PKCS1_OAEP_mgf1_with_libctx(OPENSSL_CTX *libctx,
  56                                                 unsigned char *to, int tlen,
  57                                                 const unsigned char *from,
  58                                                 int flen,
  59                                                 const unsigned char *param,
  60                                                 int plen, const EVP_MD *md,
  61                                                 const EVP_MD *mgf1md)
  62 {
  63     int rv = 0;
  64     int i, emlen = tlen - 1;
  65     unsigned char *db, *seed;
  66     unsigned char *dbmask = NULL;
  67     unsigned char seedmask[EVP_MAX_MD_SIZE];
  68     int mdlen, dbmask_len = 0;
  69
  70 #ifndef FIPS_MODULE
  71     if (md == NULL)
  72         md = EVP_sha1();
  73 #else
  74         RSAerr(0, ERR_R_PASSED_NULL_PARAMETER);
  75         return 0;
  76 #endif
  77     if (mgf1md == NULL)
  78         mgf1md = md;
  79
  80     mdlen = EVP_MD_size(md);
  81
  82     /* step 2b: check KLen > nLen - 2 HLen - 2 */
  83     if (flen > emlen - 2 * mdlen - 1) {
  84         RSAerr(0, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  85         return 0;
  86     }
  87
  88     if (emlen < 2 * mdlen + 1) {
  89         RSAerr(0, RSA_R_KEY_SIZE_TOO_SMALL);
  90         return 0;
  91     }
  92
  93     /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
  94     to[0] = 0;
  95     seed = to + 1;
  96     db = to + mdlen + 1;
  97
  98     /* step 3a: hash the additional input */
  99     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
 100         goto err;
 101     /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
 102     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
 103     /* step 3c: DB = HA || PS || 00000001 || K */
 104     db[emlen - flen - mdlen - 1] = 0x01;
 105     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
 106     /* step 3d: generate random byte string */
 107     if (RAND_bytes_ex(libctx, seed, mdlen) <= 0)
 108         goto err;
 109
 110     dbmask_len = emlen - mdlen;
 111     dbmask = OPENSSL_malloc(dbmask_len);
 112     if (dbmask == NULL) {
 113         RSAerr(0, ERR_R_MALLOC_FAILURE);
 114         goto err;
 115     }
 116
 117     /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
 118     if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
 119         goto err;
 120     /* step 3f: maskedDB = DB XOR dbMask */
 121     for (i = 0; i < dbmask_len; i++)
 122         db[i] ^= dbmask[i];
 123
 124     /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
 125     if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
 126         goto err;
 127     /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
 128     for (i = 0; i < mdlen; i++)
 129         seed[i] ^= seedmask[i];
 130     rv = 1;
 131
 132  err:
 133     OPENSSL_cleanse(seedmask, sizeof(seedmask));
 134     OPENSSL_clear_free(dbmask, dbmask_len);
 135     return rv;
 136 }
 137
 138 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 139                                     const unsigned char *from, int flen,
 140                                     const unsigned char *param, int plen,
 141                                     const EVP_MD *md, const EVP_MD *mgf1md)
 142 {
 143     return rsa_padding_add_PKCS1_OAEP_mgf1_with_libctx(NULL, to, tlen, from,
 144                                                        flen, param, plen, md,
 145                                                        mgf1md);
 146 }
 147
 148 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 149                                  const unsigned char *from, int flen, int num,
 150                                  const unsigned char *param, int plen)
 151 {
 152     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 153                                              param, plen, NULL, NULL);
 154 }
 155
 156 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 157                                       const unsigned char *from, int flen,
 158                                       int num, const unsigned char *param,
 159                                       int plen, const EVP_MD *md,
 160                                       const EVP_MD *mgf1md)
 161 {
 162     int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
 163     unsigned int good = 0, found_one_byte, mask;
 164     const unsigned char *maskedseed, *maskeddb;
 165     /*
 166      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 167      * Y || maskedSeed || maskedDB
 168      */
 169     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 170         phash[EVP_MAX_MD_SIZE];
 171     int mdlen;
 172
 173     if (md == NULL) {
 174 #ifndef FIPS_MODULE
 175         md = EVP_sha1();
 176 #else
 177         RSAerr(0, ERR_R_PASSED_NULL_PARAMETER);
 178         return -1;
 179 #endif
 180     }
 181
 182     if (mgf1md == NULL)
 183         mgf1md = md;
 184
 185     mdlen = EVP_MD_size(md);
 186
 187     if (tlen <= 0 || flen <= 0)
 188         return -1;
 189     /*
 190      * |num| is the length of the modulus; |flen| is the length of the
 191      * encoded message. Therefore, for any |from| that was obtained by
 192      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 193      * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
 194      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 195      * This does not leak any side-channel information.
 196      */
 197     if (num < flen || num < 2 * mdlen + 2) {
 198         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 199                RSA_R_OAEP_DECODING_ERROR);
 200         return -1;
 201     }
 202
 203     dblen = num - mdlen - 1;
 204     db = OPENSSL_malloc(dblen);
 205     if (db == NULL) {
 206         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 207         goto cleanup;
 208     }
 209
 210     em = OPENSSL_malloc(num);
 211     if (em == NULL) {
 212         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 213                ERR_R_MALLOC_FAILURE);
 214         goto cleanup;
 215     }
 216
 217     /*
 218      * Caller is encouraged to pass zero-padded message created with
 219      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 220      * bounds, it's impossible to have an invariant memory access pattern
 221      * in case |from| was not zero-padded in advance.
 222      */
 223     for (from += flen, em += num, i = 0; i < num; i++) {
 224         mask = ~constant_time_is_zero(flen);
 225         flen -= 1 & mask;
 226         from -= 1 & mask;
 227         *--em = *from & mask;
 228     }
 229
 230     /*
 231      * The first byte must be zero, however we must not leak if this is
 232      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 233      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 234      */
 235     good = constant_time_is_zero(em[0]);
 236
 237     maskedseed = em + 1;
 238     maskeddb = em + 1 + mdlen;
 239
 240     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 241         goto cleanup;
 242     for (i = 0; i < mdlen; i++)
 243         seed[i] ^= maskedseed[i];
 244
 245     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 246         goto cleanup;
 247     for (i = 0; i < dblen; i++)
 248         db[i] ^= maskeddb[i];
 249
 250     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 251         goto cleanup;
 252
 253     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 254
 255     found_one_byte = 0;
 256     for (i = mdlen; i < dblen; i++) {
 257         /*
 258          * Padding consists of a number of 0-bytes, followed by a 1.
 259          */
 260         unsigned int equals1 = constant_time_eq(db[i], 1);
 261         unsigned int equals0 = constant_time_is_zero(db[i]);
 262         one_index = constant_time_select_int(~found_one_byte & equals1,
 263                                              i, one_index);
 264         found_one_byte |= equals1;
 265         good &= (found_one_byte | equals0);
 266     }
 267
 268     good &= found_one_byte;
 269
 270     /*
 271      * At this point |good| is zero unless the plaintext was valid,
 272      * so plaintext-awareness ensures timing side-channels are no longer a
 273      * concern.
 274      */
 275     msg_index = one_index + 1;
 276     mlen = dblen - msg_index;
 277
 278     /*
 279      * For good measure, do this check in constant time as well.
 280      */
 281     good &= constant_time_ge(tlen, mlen);
 282
 283     /*
 284      * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
 285      * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
 286      * Otherwise leave |to| unchanged.
 287      * Copy the memory back in a way that does not reveal the size of
 288      * the data being copied via a timing side channel. This requires copying
 289      * parts of the buffer multiple times based on the bits set in the real
 290      * length. Clear bits do a non-copy with identical access pattern.
 291      * The loop below has overall complexity of O(N*log(N)).
 292      */
 293     tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
 294                                     dblen - mdlen - 1, tlen);
 295     for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
 296         mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
 297         for (i = mdlen + 1; i < dblen - msg_index; i++)
 298             db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
 299     }
 300     for (i = 0; i < tlen; i++) {
 301         mask = good & constant_time_lt(i, mlen);
 302         to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
 303     }
 304
 305 #ifndef FIPS_MODULE
 306     /*
 307      * To avoid chosen ciphertext attacks, the error message should not
 308      * reveal which kind of decoding error happened.
 309      *
 310      * This trick doesn't work in the FIPS provider because libcrypto manages
 311      * the error stack. Instead we opt not to put an error on the stack at all
 312      * in case of padding failure in the FIPS provider.
 313      */
 314     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 315            RSA_R_OAEP_DECODING_ERROR);
 316     err_clear_last_constant_time(1 & good);
 317 #endif
 318  cleanup:
 319     OPENSSL_cleanse(seed, sizeof(seed));
 320     OPENSSL_clear_free(db, dblen);
 321     OPENSSL_clear_free(em, num);
 322
 323     return constant_time_select_int(good, mlen, -1);
 324 }
 325
 326 /*
 327  * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
 328  * The variables are named differently to NIST:
 329  *      mask (T) and len (maskLen)are the returned mask.
 330  *      seed (mgfSeed).
 331  * The range checking steps inm the process are performed outside.
 332  */
 333 int PKCS1_MGF1(unsigned char *mask, long len,
 334                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 335 {
 336     long i, outlen = 0;
 337     unsigned char cnt[4];
 338     EVP_MD_CTX *c = EVP_MD_CTX_new();
 339     unsigned char md[EVP_MAX_MD_SIZE];
 340     int mdlen;
 341     int rv = -1;
 342
 343     if (c == NULL)
 344         goto err;
 345     mdlen = EVP_MD_size(dgst);
 346     if (mdlen < 0)
 347         goto err;
 348     /* step 4 */
 349     for (i = 0; outlen < len; i++) {
 350         /* step 4a: D = I2BS(counter, 4) */
 351         cnt[0] = (unsigned char)((i >> 24) & 255);
 352         cnt[1] = (unsigned char)((i >> 16) & 255);
 353         cnt[2] = (unsigned char)((i >> 8)) & 255;
 354         cnt[3] = (unsigned char)(i & 255);
 355         /* step 4b: T =T || hash(mgfSeed || D) */
 356         if (!EVP_DigestInit_ex(c, dgst, NULL)
 357             || !EVP_DigestUpdate(c, seed, seedlen)
 358             || !EVP_DigestUpdate(c, cnt, 4))
 359             goto err;
 360         if (outlen + mdlen <= len) {
 361             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 362                 goto err;
 363             outlen += mdlen;
 364         } else {
 365             if (!EVP_DigestFinal_ex(c, md, NULL))
 366                 goto err;
 367             memcpy(mask + outlen, md, len - outlen);
 368             outlen = len;
 369         }
 370     }
 371     rv = 0;
 372  err:
 373     OPENSSL_cleanse(md, sizeof(md));
 374     EVP_MD_CTX_free(c);
 375     return rv;
 376 }