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     if (md == NULL) {
  71 #ifndef FIPS_MODULE
  72         md = EVP_sha1();
  73 #else
  74         RSAerr(0, ERR_R_PASSED_NULL_PARAMETER);
  75         return 0;
  76 #endif
  77     }
  78     if (mgf1md == NULL)
  79         mgf1md = md;
  80
  81     mdlen = EVP_MD_size(md);
  82
  83     /* step 2b: check KLen > nLen - 2 HLen - 2 */
  84     if (flen > emlen - 2 * mdlen - 1) {
  85         RSAerr(0, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  86         return 0;
  87     }
  88
  89     if (emlen < 2 * mdlen + 1) {
  90         RSAerr(0, RSA_R_KEY_SIZE_TOO_SMALL);
  91         return 0;
  92     }
  93
  94     /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
  95     to[0] = 0;
  96     seed = to + 1;
  97     db = to + mdlen + 1;
  98
  99     /* step 3a: hash the additional input */
 100     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
 101         goto err;
 102     /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
 103     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
 104     /* step 3c: DB = HA || PS || 00000001 || K */
 105     db[emlen - flen - mdlen - 1] = 0x01;
 106     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
 107     /* step 3d: generate random byte string */
 108     if (RAND_bytes_ex(libctx, seed, mdlen) <= 0)
 109         goto err;
 110
 111     dbmask_len = emlen - mdlen;
 112     dbmask = OPENSSL_malloc(dbmask_len);
 113     if (dbmask == NULL) {
 114         RSAerr(0, ERR_R_MALLOC_FAILURE);
 115         goto err;
 116     }
 117
 118     /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
 119     if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
 120         goto err;
 121     /* step 3f: maskedDB = DB XOR dbMask */
 122     for (i = 0; i < dbmask_len; i++)
 123         db[i] ^= dbmask[i];
 124
 125     /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
 126     if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
 127         goto err;
 128     /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
 129     for (i = 0; i < mdlen; i++)
 130         seed[i] ^= seedmask[i];
 131     rv = 1;
 132
 133  err:
 134     OPENSSL_cleanse(seedmask, sizeof(seedmask));
 135     OPENSSL_clear_free(dbmask, dbmask_len);
 136     return rv;
 137 }
 138
 139 int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 140                                     const unsigned char *from, int flen,
 141                                     const unsigned char *param, int plen,
 142                                     const EVP_MD *md, const EVP_MD *mgf1md)
 143 {
 144     return rsa_padding_add_PKCS1_OAEP_mgf1_with_libctx(NULL, to, tlen, from,
 145                                                        flen, param, plen, md,
 146                                                        mgf1md);
 147 }
 148
 149 int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
 150                                  const unsigned char *from, int flen, int num,
 151                                  const unsigned char *param, int plen)
 152 {
 153     return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
 154                                              param, plen, NULL, NULL);
 155 }
 156
 157 int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
 158                                       const unsigned char *from, int flen,
 159                                       int num, const unsigned char *param,
 160                                       int plen, const EVP_MD *md,
 161                                       const EVP_MD *mgf1md)
 162 {
 163     int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
 164     unsigned int good = 0, found_one_byte, mask;
 165     const unsigned char *maskedseed, *maskeddb;
 166     /*
 167      * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
 168      * Y || maskedSeed || maskedDB
 169      */
 170     unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
 171         phash[EVP_MAX_MD_SIZE];
 172     int mdlen;
 173
 174     if (md == NULL) {
 175 #ifndef FIPS_MODULE
 176         md = EVP_sha1();
 177 #else
 178         RSAerr(0, ERR_R_PASSED_NULL_PARAMETER);
 179         return -1;
 180 #endif
 181     }
 182
 183     if (mgf1md == NULL)
 184         mgf1md = md;
 185
 186     mdlen = EVP_MD_size(md);
 187
 188     if (tlen <= 0 || flen <= 0)
 189         return -1;
 190     /*
 191      * |num| is the length of the modulus; |flen| is the length of the
 192      * encoded message. Therefore, for any |from| that was obtained by
 193      * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
 194      * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
 195      * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
 196      * This does not leak any side-channel information.
 197      */
 198     if (num < flen || num < 2 * mdlen + 2) {
 199         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 200                RSA_R_OAEP_DECODING_ERROR);
 201         return -1;
 202     }
 203
 204     dblen = num - mdlen - 1;
 205     db = OPENSSL_malloc(dblen);
 206     if (db == NULL) {
 207         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
 208         goto cleanup;
 209     }
 210
 211     em = OPENSSL_malloc(num);
 212     if (em == NULL) {
 213         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 214                ERR_R_MALLOC_FAILURE);
 215         goto cleanup;
 216     }
 217
 218     /*
 219      * Caller is encouraged to pass zero-padded message created with
 220      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 221      * bounds, it's impossible to have an invariant memory access pattern
 222      * in case |from| was not zero-padded in advance.
 223      */
 224     for (from += flen, em += num, i = 0; i < num; i++) {
 225         mask = ~constant_time_is_zero(flen);
 226         flen -= 1 & mask;
 227         from -= 1 & mask;
 228         *--em = *from & mask;
 229     }
 230
 231     /*
 232      * The first byte must be zero, however we must not leak if this is
 233      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 234      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 235      */
 236     good = constant_time_is_zero(em[0]);
 237
 238     maskedseed = em + 1;
 239     maskeddb = em + 1 + mdlen;
 240
 241     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 242         goto cleanup;
 243     for (i = 0; i < mdlen; i++)
 244         seed[i] ^= maskedseed[i];
 245
 246     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 247         goto cleanup;
 248     for (i = 0; i < dblen; i++)
 249         db[i] ^= maskeddb[i];
 250
 251     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 252         goto cleanup;
 253
 254     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 255
 256     found_one_byte = 0;
 257     for (i = mdlen; i < dblen; i++) {
 258         /*
 259          * Padding consists of a number of 0-bytes, followed by a 1.
 260          */
 261         unsigned int equals1 = constant_time_eq(db[i], 1);
 262         unsigned int equals0 = constant_time_is_zero(db[i]);
 263         one_index = constant_time_select_int(~found_one_byte & equals1,
 264                                              i, one_index);
 265         found_one_byte |= equals1;
 266         good &= (found_one_byte | equals0);
 267     }
 268
 269     good &= found_one_byte;
 270
 271     /*
 272      * At this point |good| is zero unless the plaintext was valid,
 273      * so plaintext-awareness ensures timing side-channels are no longer a
 274      * concern.
 275      */
 276     msg_index = one_index + 1;
 277     mlen = dblen - msg_index;
 278
 279     /*
 280      * For good measure, do this check in constant time as well.
 281      */
 282     good &= constant_time_ge(tlen, mlen);
 283
 284     /*
 285      * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
 286      * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
 287      * Otherwise leave |to| unchanged.
 288      * Copy the memory back in a way that does not reveal the size of
 289      * the data being copied via a timing side channel. This requires copying
 290      * parts of the buffer multiple times based on the bits set in the real
 291      * length. Clear bits do a non-copy with identical access pattern.
 292      * The loop below has overall complexity of O(N*log(N)).
 293      */
 294     tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
 295                                     dblen - mdlen - 1, tlen);
 296     for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
 297         mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
 298         for (i = mdlen + 1; i < dblen - msg_index; i++)
 299             db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
 300     }
 301     for (i = 0; i < tlen; i++) {
 302         mask = good & constant_time_lt(i, mlen);
 303         to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
 304     }
 305
 306 #ifndef FIPS_MODULE
 307     /*
 308      * To avoid chosen ciphertext attacks, the error message should not
 309      * reveal which kind of decoding error happened.
 310      *
 311      * This trick doesn't work in the FIPS provider because libcrypto manages
 312      * the error stack. Instead we opt not to put an error on the stack at all
 313      * in case of padding failure in the FIPS provider.
 314      */
 315     RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
 316            RSA_R_OAEP_DECODING_ERROR);
 317     err_clear_last_constant_time(1 & good);
 318 #endif
 319  cleanup:
 320     OPENSSL_cleanse(seed, sizeof(seed));
 321     OPENSSL_clear_free(db, dblen);
 322     OPENSSL_clear_free(em, num);
 323
 324     return constant_time_select_int(good, mlen, -1);
 325 }
 326
 327 /*
 328  * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
 329  * The variables are named differently to NIST:
 330  *      mask (T) and len (maskLen)are the returned mask.
 331  *      seed (mgfSeed).
 332  * The range checking steps inm the process are performed outside.
 333  */
 334 int PKCS1_MGF1(unsigned char *mask, long len,
 335                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 336 {
 337     long i, outlen = 0;
 338     unsigned char cnt[4];
 339     EVP_MD_CTX *c = EVP_MD_CTX_new();
 340     unsigned char md[EVP_MAX_MD_SIZE];
 341     int mdlen;
 342     int rv = -1;
 343
 344     if (c == NULL)
 345         goto err;
 346     mdlen = EVP_MD_size(dgst);
 347     if (mdlen < 0)
 348         goto err;
 349     /* step 4 */
 350     for (i = 0; outlen < len; i++) {
 351         /* step 4a: D = I2BS(counter, 4) */
 352         cnt[0] = (unsigned char)((i >> 24) & 255);
 353         cnt[1] = (unsigned char)((i >> 16) & 255);
 354         cnt[2] = (unsigned char)((i >> 8)) & 255;
 355         cnt[3] = (unsigned char)(i & 255);
 356         /* step 4b: T =T || hash(mgfSeed || D) */
 357         if (!EVP_DigestInit_ex(c, dgst, NULL)
 358             || !EVP_DigestUpdate(c, seed, seedlen)
 359             || !EVP_DigestUpdate(c, cnt, 4))
 360             goto err;
 361         if (outlen + mdlen <= len) {
 362             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 363                 goto err;
 364             outlen += mdlen;
 365         } else {
 366             if (!EVP_DigestFinal_ex(c, md, NULL))
 367                 goto err;
 368             memcpy(mask + outlen, md, len - outlen);
 369             outlen = len;
 370         }
 371     }
 372     rv = 0;
 373  err:
 374     OPENSSL_cleanse(md, sizeof(md));
 375     EVP_MD_CTX_free(c);
 376     return rv;
 377 }