crypto/rsa/rsa_oaep.c

   1 /*
   2  * Copyright 1999-2021 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 ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
  44                                                    param, plen, NULL, NULL);
  45 }
  46
  47 /*
  48  * Perform the padding as per NIST 800-56B 7.2.2.3
  49  *      from (K) is the key material.
  50  *      param (A) is the additional input.
  51  * Step numbers are included here but not in the constant time inverse below
  52  * to avoid complicating an already difficult enough function.
  53  */
  54 int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx,
  55                                             unsigned char *to, int tlen,
  56                                             const unsigned char *from, int flen,
  57                                             const unsigned char *param,
  58                                             int plen, const EVP_MD *md,
  59                                             const EVP_MD *mgf1md)
  60 {
  61     int rv = 0;
  62     int i, emlen = tlen - 1;
  63     unsigned char *db, *seed;
  64     unsigned char *dbmask = NULL;
  65     unsigned char seedmask[EVP_MAX_MD_SIZE];
  66     int mdlen, dbmask_len = 0;
  67
  68     if (md == NULL) {
  69 #ifndef FIPS_MODULE
  70         md = EVP_sha1();
  71 #else
  72         ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
  73         return 0;
  74 #endif
  75     }
  76     if (mgf1md == NULL)
  77         mgf1md = md;
  78
  79     mdlen = EVP_MD_get_size(md);
  80     if (mdlen <= 0) {
  81         ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
  82         return 0;
  83     }
  84
  85     /* step 2b: check KLen > nLen - 2 HLen - 2 */
  86     if (flen > emlen - 2 * mdlen - 1) {
  87         ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  88         return 0;
  89     }
  90
  91     if (emlen < 2 * mdlen + 1) {
  92         ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL);
  93         return 0;
  94     }
  95
  96     /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
  97     to[0] = 0;
  98     seed = to + 1;
  99     db = to + mdlen + 1;
 100
 101     /* step 3a: hash the additional input */
 102     if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
 103         goto err;
 104     /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
 105     memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
 106     /* step 3c: DB = HA || PS || 00000001 || K */
 107     db[emlen - flen - mdlen - 1] = 0x01;
 108     memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
 109     /* step 3d: generate random byte string */
 110     if (RAND_bytes_ex(libctx, seed, mdlen, 0) <= 0)
 111         goto err;
 112
 113     dbmask_len = emlen - mdlen;
 114     dbmask = OPENSSL_malloc(dbmask_len);
 115     if (dbmask == NULL)
 116         goto err;
 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 ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
 145                                                    param, plen, md, 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         ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
 178         return -1;
 179 #endif
 180     }
 181
 182     if (mgf1md == NULL)
 183         mgf1md = md;
 184
 185     mdlen = EVP_MD_get_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         ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
 199         return -1;
 200     }
 201
 202     dblen = num - mdlen - 1;
 203     db = OPENSSL_malloc(dblen);
 204     if (db == NULL)
 205         goto cleanup;
 206
 207     em = OPENSSL_malloc(num);
 208     if (em == NULL)
 209         goto cleanup;
 210
 211     /*
 212      * Caller is encouraged to pass zero-padded message created with
 213      * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
 214      * bounds, it's impossible to have an invariant memory access pattern
 215      * in case |from| was not zero-padded in advance.
 216      */
 217     for (from += flen, em += num, i = 0; i < num; i++) {
 218         mask = ~constant_time_is_zero(flen);
 219         flen -= 1 & mask;
 220         from -= 1 & mask;
 221         *--em = *from & mask;
 222     }
 223
 224     /*
 225      * The first byte must be zero, however we must not leak if this is
 226      * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
 227      * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
 228      */
 229     good = constant_time_is_zero(em[0]);
 230
 231     maskedseed = em + 1;
 232     maskeddb = em + 1 + mdlen;
 233
 234     if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
 235         goto cleanup;
 236     for (i = 0; i < mdlen; i++)
 237         seed[i] ^= maskedseed[i];
 238
 239     if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
 240         goto cleanup;
 241     for (i = 0; i < dblen; i++)
 242         db[i] ^= maskeddb[i];
 243
 244     if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
 245         goto cleanup;
 246
 247     good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
 248
 249     found_one_byte = 0;
 250     for (i = mdlen; i < dblen; i++) {
 251         /*
 252          * Padding consists of a number of 0-bytes, followed by a 1.
 253          */
 254         unsigned int equals1 = constant_time_eq(db[i], 1);
 255         unsigned int equals0 = constant_time_is_zero(db[i]);
 256         one_index = constant_time_select_int(~found_one_byte & equals1,
 257                                              i, one_index);
 258         found_one_byte |= equals1;
 259         good &= (found_one_byte | equals0);
 260     }
 261
 262     good &= found_one_byte;
 263
 264     /*
 265      * At this point |good| is zero unless the plaintext was valid,
 266      * so plaintext-awareness ensures timing side-channels are no longer a
 267      * concern.
 268      */
 269     msg_index = one_index + 1;
 270     mlen = dblen - msg_index;
 271
 272     /*
 273      * For good measure, do this check in constant time as well.
 274      */
 275     good &= constant_time_ge(tlen, mlen);
 276
 277     /*
 278      * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
 279      * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
 280      * Otherwise leave |to| unchanged.
 281      * Copy the memory back in a way that does not reveal the size of
 282      * the data being copied via a timing side channel. This requires copying
 283      * parts of the buffer multiple times based on the bits set in the real
 284      * length. Clear bits do a non-copy with identical access pattern.
 285      * The loop below has overall complexity of O(N*log(N)).
 286      */
 287     tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
 288                                     dblen - mdlen - 1, tlen);
 289     for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
 290         mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
 291         for (i = mdlen + 1; i < dblen - msg_index; i++)
 292             db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
 293     }
 294     for (i = 0; i < tlen; i++) {
 295         mask = good & constant_time_lt(i, mlen);
 296         to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
 297     }
 298
 299 #ifndef FIPS_MODULE
 300     /*
 301      * To avoid chosen ciphertext attacks, the error message should not
 302      * reveal which kind of decoding error happened.
 303      *
 304      * This trick doesn't work in the FIPS provider because libcrypto manages
 305      * the error stack. Instead we opt not to put an error on the stack at all
 306      * in case of padding failure in the FIPS provider.
 307      */
 308     ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
 309     err_clear_last_constant_time(1 & good);
 310 #endif
 311  cleanup:
 312     OPENSSL_cleanse(seed, sizeof(seed));
 313     OPENSSL_clear_free(db, dblen);
 314     OPENSSL_clear_free(em, num);
 315
 316     return constant_time_select_int(good, mlen, -1);
 317 }
 318
 319 /*
 320  * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
 321  * The variables are named differently to NIST:
 322  *      mask (T) and len (maskLen)are the returned mask.
 323  *      seed (mgfSeed).
 324  * The range checking steps inm the process are performed outside.
 325  */
 326 int PKCS1_MGF1(unsigned char *mask, long len,
 327                const unsigned char *seed, long seedlen, const EVP_MD *dgst)
 328 {
 329     long i, outlen = 0;
 330     unsigned char cnt[4];
 331     EVP_MD_CTX *c = EVP_MD_CTX_new();
 332     unsigned char md[EVP_MAX_MD_SIZE];
 333     int mdlen;
 334     int rv = -1;
 335
 336     if (c == NULL)
 337         goto err;
 338     mdlen = EVP_MD_get_size(dgst);
 339     if (mdlen < 0)
 340         goto err;
 341     /* step 4 */
 342     for (i = 0; outlen < len; i++) {
 343         /* step 4a: D = I2BS(counter, 4) */
 344         cnt[0] = (unsigned char)((i >> 24) & 255);
 345         cnt[1] = (unsigned char)((i >> 16) & 255);
 346         cnt[2] = (unsigned char)((i >> 8)) & 255;
 347         cnt[3] = (unsigned char)(i & 255);
 348         /* step 4b: T =T || hash(mgfSeed || D) */
 349         if (!EVP_DigestInit_ex(c, dgst, NULL)
 350             || !EVP_DigestUpdate(c, seed, seedlen)
 351             || !EVP_DigestUpdate(c, cnt, 4))
 352             goto err;
 353         if (outlen + mdlen <= len) {
 354             if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
 355                 goto err;
 356             outlen += mdlen;
 357         } else {
 358             if (!EVP_DigestFinal_ex(c, md, NULL))
 359                 goto err;
 360             memcpy(mask + outlen, md, len - outlen);
 361             outlen = len;
 362         }
 363     }
 364     rv = 0;
 365  err:
 366     OPENSSL_cleanse(md, sizeof(md));
 367     EVP_MD_CTX_free(c);
 368     return rv;
 369 }