text: /*
   * Copyright 1999-2020 The OpenSSL Project Authors. All Rights Reserved.
   *
   * Licensed under the Apache License 2.0 (the "License").  You may not use
   * this file except in compliance with the License.  You can obtain a copy
   * in the file LICENSE in the source distribution or at
   * https://www.openssl.org/source/license.html
   */
  
  /* EME-OAEP as defined in RFC 2437 (PKCS #1 v2.0) */
  
  /*
   * See Victor Shoup, "OAEP reconsidered," Nov. 2000, <URL:
   * http://www.shoup.net/papers/oaep.ps.Z> for problems with the security
   * proof for the original OAEP scheme, which EME-OAEP is based on. A new
   * proof can be found in E. Fujisaki, T. Okamoto, D. Pointcheval, J. Stern,
   * "RSA-OEAP is Still Alive!", Dec. 2000, <URL:
   * http://eprint.iacr.org/2000/061/>. The new proof has stronger requirements
   * for the underlying permutation: "partial-one-wayness" instead of
   * one-wayness.  For the RSA function, this is an equivalent notion.
   */
  
  /*
   * RSA low level APIs are deprecated for public use, but still ok for
   * internal use.
   */
  #include "internal/deprecated.h"
  
  #include "internal/constant_time.h"
  
  #include <stdio.h>
  #include "internal/cryptlib.h"
  #include <openssl/bn.h>
  #include <openssl/evp.h>
  #include <openssl/rand.h>
  #include <openssl/sha.h>
  #include "rsa_local.h"
  
  int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
                                 const unsigned char *from, int flen,
                                 const unsigned char *param, int plen)
  {
      return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
                                                     param, plen, NULL, NULL);
  }
  
  /*
   * Perform the padding as per NIST 800-56B 7.2.2.3
   *      from (K) is the key material.
   *      param (A) is the additional input.
   * Step numbers are included here but not in the constant time inverse below
   * to avoid complicating an already difficult enough function.
   */
  int ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(OSSL_LIB_CTX *libctx,
                                              unsigned char *to, int tlen,
                                              const unsigned char *from, int flen,
                                              const unsigned char *param,
                                              int plen, const EVP_MD *md,
                                              const EVP_MD *mgf1md)
  {
      int rv = 0;
      int i, emlen = tlen - 1;
      unsigned char *db, *seed;
      unsigned char *dbmask = NULL;
      unsigned char seedmask[EVP_MAX_MD_SIZE];
      int mdlen, dbmask_len = 0;
  
      if (md == NULL) {
  #ifndef FIPS_MODULE
          md = EVP_sha1();
  #else
          ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
          return 0;
  #endif
      }
      if (mgf1md == NULL)
          mgf1md = md;
  
      mdlen = EVP_MD_size(md);
  
      /* step 2b: check KLen > nLen - 2 HLen - 2 */
      if (flen > emlen - 2 * mdlen - 1) {
          ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
          return 0;
      }
  
      if (emlen < 2 * mdlen + 1) {
          ERR_raise(ERR_LIB_RSA, RSA_R_KEY_SIZE_TOO_SMALL);
          return 0;
      }
  
      /* step 3i: EM = 00000000 || maskedMGF || maskedDB */
      to[0] = 0;
      seed = to + 1;
      db = to + mdlen + 1;
  
      /* step 3a: hash the additional input */
      if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
          goto err;
      /* step 3b: zero bytes array of length nLen - KLen - 2 HLen -2 */
      memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
      /* step 3c: DB = HA || PS || 00000001 || K */
      db[emlen - flen - mdlen - 1] = 0x01;
      memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
      /* step 3d: generate random byte string */
      if (RAND_bytes_ex(libctx, seed, mdlen) <= 0)
          goto err;
  
      dbmask_len = emlen - mdlen;
      dbmask = OPENSSL_malloc(dbmask_len);
      if (dbmask == NULL) {
          ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
          goto err;
      }
  
      /* step 3e: dbMask = MGF(mgfSeed, nLen - HLen - 1) */
      if (PKCS1_MGF1(dbmask, dbmask_len, seed, mdlen, mgf1md) < 0)
          goto err;
      /* step 3f: maskedDB = DB XOR dbMask */
      for (i = 0; i < dbmask_len; i++)
          db[i] ^= dbmask[i];
  
      /* step 3g: mgfSeed = MGF(maskedDB, HLen) */
      if (PKCS1_MGF1(seedmask, mdlen, db, dbmask_len, mgf1md) < 0)
          goto err;
      /* stepo 3h: maskedMGFSeed = mgfSeed XOR mgfSeedMask */
      for (i = 0; i < mdlen; i++)
          seed[i] ^= seedmask[i];
      rv = 1;
  
   err:
      OPENSSL_cleanse(seedmask, sizeof(seedmask));
      OPENSSL_clear_free(dbmask, dbmask_len);
      return rv;
  }
  
  int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
                                      const unsigned char *from, int flen,
                                      const unsigned char *param, int plen,
                                      const EVP_MD *md, const EVP_MD *mgf1md)
  {
      return ossl_rsa_padding_add_PKCS1_OAEP_mgf1_ex(NULL, to, tlen, from, flen,
                                                     param, plen, md, mgf1md);
  }
  
  int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
                                   const unsigned char *from, int flen, int num,
                                   const unsigned char *param, int plen)
  {
      return RSA_padding_check_PKCS1_OAEP_mgf1(to, tlen, from, flen, num,
                                               param, plen, NULL, NULL);
  }
  
  int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
                                        const unsigned char *from, int flen,
                                        int num, const unsigned char *param,
                                        int plen, const EVP_MD *md,
                                        const EVP_MD *mgf1md)
  {
      int i, dblen = 0, mlen = -1, one_index = 0, msg_index;
      unsigned int good = 0, found_one_byte, mask;
      const unsigned char *maskedseed, *maskeddb;
      /*
       * |em| is the encoded message, zero-padded to exactly |num| bytes: em =
       * Y || maskedSeed || maskedDB
       */
      unsigned char *db = NULL, *em = NULL, seed[EVP_MAX_MD_SIZE],
          phash[EVP_MAX_MD_SIZE];
      int mdlen;
  
      if (md == NULL) {
  #ifndef FIPS_MODULE
          md = EVP_sha1();
  #else
          ERR_raise(ERR_LIB_RSA, ERR_R_PASSED_NULL_PARAMETER);
          return -1;
  #endif
      }
  
      if (mgf1md == NULL)
          mgf1md = md;
  
      mdlen = EVP_MD_size(md);
  
      if (tlen <= 0 || flen <= 0)
          return -1;
      /*
       * |num| is the length of the modulus; |flen| is the length of the
       * encoded message. Therefore, for any |from| that was obtained by
       * decrypting a ciphertext, we must have |flen| <= |num|. Similarly,
       * |num| >= 2 * |mdlen| + 2 must hold for the modulus irrespective of
       * the ciphertext, see PKCS #1 v2.2, section 7.1.2.
       * This does not leak any side-channel information.
       */
      if (num < flen || num < 2 * mdlen + 2) {
          ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
          return -1;
      }
  
      dblen = num - mdlen - 1;
      db = OPENSSL_malloc(dblen);
      if (db == NULL) {
          ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
          goto cleanup;
      }
  
      em = OPENSSL_malloc(num);
      if (em == NULL) {
          ERR_raise(ERR_LIB_RSA, ERR_R_MALLOC_FAILURE);
          goto cleanup;
      }
  
      /*
       * Caller is encouraged to pass zero-padded message created with
       * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
       * bounds, it's impossible to have an invariant memory access pattern
       * in case |from| was not zero-padded in advance.
       */
      for (from += flen, em += num, i = 0; i < num; i++) {
          mask = ~constant_time_is_zero(flen);
          flen -= 1 & mask;
          from -= 1 & mask;
          *--em = *from & mask;
      }
  
      /*
       * The first byte must be zero, however we must not leak if this is
       * true. See James H. Manger, "A Chosen Ciphertext  Attack on RSA
       * Optimal Asymmetric Encryption Padding (OAEP) [...]", CRYPTO 2001).
       */
      good = constant_time_is_zero(em[0]);
  
      maskedseed = em + 1;
      maskeddb = em + 1 + mdlen;
  
      if (PKCS1_MGF1(seed, mdlen, maskeddb, dblen, mgf1md))
          goto cleanup;
      for (i = 0; i < mdlen; i++)
          seed[i] ^= maskedseed[i];
  
      if (PKCS1_MGF1(db, dblen, seed, mdlen, mgf1md))
          goto cleanup;
      for (i = 0; i < dblen; i++)
          db[i] ^= maskeddb[i];
  
      if (!EVP_Digest((void *)param, plen, phash, NULL, md, NULL))
          goto cleanup;
  
      good &= constant_time_is_zero(CRYPTO_memcmp(db, phash, mdlen));
  
      found_one_byte = 0;
      for (i = mdlen; i < dblen; i++) {
          /*
           * Padding consists of a number of 0-bytes, followed by a 1.
           */
          unsigned int equals1 = constant_time_eq(db[i], 1);
          unsigned int equals0 = constant_time_is_zero(db[i]);
          one_index = constant_time_select_int(~found_one_byte & equals1,
                                               i, one_index);
          found_one_byte |= equals1;
          good &= (found_one_byte | equals0);
      }
  
      good &= found_one_byte;
  
      /*
       * At this point |good| is zero unless the plaintext was valid,
       * so plaintext-awareness ensures timing side-channels are no longer a
       * concern.
       */
      msg_index = one_index + 1;
      mlen = dblen - msg_index;
  
      /*
       * For good measure, do this check in constant time as well.
       */
      good &= constant_time_ge(tlen, mlen);
  
      /*
       * Move the result in-place by |dblen|-|mdlen|-1-|mlen| bytes to the left.
       * Then if |good| move |mlen| bytes from |db|+|mdlen|+1 to |to|.
       * Otherwise leave |to| unchanged.
       * Copy the memory back in a way that does not reveal the size of
       * the data being copied via a timing side channel. This requires copying
       * parts of the buffer multiple times based on the bits set in the real
       * length. Clear bits do a non-copy with identical access pattern.
       * The loop below has overall complexity of O(N*log(N)).
       */
      tlen = constant_time_select_int(constant_time_lt(dblen - mdlen - 1, tlen),
                                      dblen - mdlen - 1, tlen);
      for (msg_index = 1; msg_index < dblen - mdlen - 1; msg_index <<= 1) {
          mask = ~constant_time_eq(msg_index & (dblen - mdlen - 1 - mlen), 0);
          for (i = mdlen + 1; i < dblen - msg_index; i++)
              db[i] = constant_time_select_8(mask, db[i + msg_index], db[i]);
      }
      for (i = 0; i < tlen; i++) {
          mask = good & constant_time_lt(i, mlen);
          to[i] = constant_time_select_8(mask, db[i + mdlen + 1], to[i]);
      }
  
  #ifndef FIPS_MODULE
      /*
       * To avoid chosen ciphertext attacks, the error message should not
       * reveal which kind of decoding error happened.
       *
       * This trick doesn't work in the FIPS provider because libcrypto manages
       * the error stack. Instead we opt not to put an error on the stack at all
       * in case of padding failure in the FIPS provider.
       */
      ERR_raise(ERR_LIB_RSA, RSA_R_OAEP_DECODING_ERROR);
      err_clear_last_constant_time(1 & good);
  #endif
   cleanup:
      OPENSSL_cleanse(seed, sizeof(seed));
      OPENSSL_clear_free(db, dblen);
      OPENSSL_clear_free(em, num);
  
      return constant_time_select_int(good, mlen, -1);
  }
  
  /*
   * Mask Generation Function corresponding to section 7.2.2.2 of NIST SP 800-56B.
   * The variables are named differently to NIST:
   *      mask (T) and len (maskLen)are the returned mask.
   *      seed (mgfSeed).
   * The range checking steps inm the process are performed outside.
   */
  int PKCS1_MGF1(unsigned char *mask, long len,
                 const unsigned char *seed, long seedlen, const EVP_MD *dgst)
  {
      long i, outlen = 0;
      unsigned char cnt[4];
      EVP_MD_CTX *c = EVP_MD_CTX_new();
      unsigned char md[EVP_MAX_MD_SIZE];
      int mdlen;
      int rv = -1;
  
      if (c == NULL)
          goto err;
      mdlen = EVP_MD_size(dgst);
      if (mdlen < 0)
          goto err;
      /* step 4 */
      for (i = 0; outlen < len; i++) {
          /* step 4a: D = I2BS(counter, 4) */
          cnt[0] = (unsigned char)((i >> 24) & 255);
          cnt[1] = (unsigned char)((i >> 16) & 255);
          cnt[2] = (unsigned char)((i >> 8)) & 255;
          cnt[3] = (unsigned char)(i & 255);
          /* step 4b: T =T || hash(mgfSeed || D) */
          if (!EVP_DigestInit_ex(c, dgst, NULL)
              || !EVP_DigestUpdate(c, seed, seedlen)
              || !EVP_DigestUpdate(c, cnt, 4))
              goto err;
          if (outlen + mdlen <= len) {
              if (!EVP_DigestFinal_ex(c, mask + outlen, NULL))
                  goto err;
              outlen += mdlen;
          } else {
              if (!EVP_DigestFinal_ex(c, md, NULL))
                  goto err;
              memcpy(mask + outlen, md, len - outlen);
              outlen = len;
          }
      }
      rv = 0;
   err:
      OPENSSL_cleanse(md, sizeof(md));
      EVP_MD_CTX_free(c);
      return rv;
  }
  