text: /*
   * Written by Ulf Moeller. This software is distributed on an "AS IS" basis,
   * WITHOUT WARRANTY OF ANY KIND, either express or implied.
   */
  
  /* 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.
   */
  
  #include "internal/constant_time_locl.h"
  
  #include <stdio.h>
  #include "internal/cryptlib.h"
  #include <openssl/bn.h>
  #include <openssl/rsa.h>
  #include <openssl/evp.h>
  #include <openssl/rand.h>
  #include <openssl/sha.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 RSA_padding_add_PKCS1_OAEP_mgf1(to, tlen, from, flen,
                                             param, plen, NULL, NULL);
  }
  
  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)
  {
      int i, emlen = tlen - 1;
      unsigned char *db, *seed;
      unsigned char *dbmask, seedmask[EVP_MAX_MD_SIZE];
      int mdlen;
  
      if (md == NULL)
          md = EVP_sha1();
      if (mgf1md == NULL)
          mgf1md = md;
  
      mdlen = EVP_MD_size(md);
  
      if (flen > emlen - 2 * mdlen - 1) {
          RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
                 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
          return 0;
      }
  
      if (emlen < 2 * mdlen + 1) {
          RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1,
                 RSA_R_KEY_SIZE_TOO_SMALL);
          return 0;
      }
  
      to[0] = 0;
      seed = to + 1;
      db = to + mdlen + 1;
  
      if (!EVP_Digest((void *)param, plen, db, NULL, md, NULL))
          return 0;
      memset(db + mdlen, 0, emlen - flen - 2 * mdlen - 1);
      db[emlen - flen - mdlen - 1] = 0x01;
      memcpy(db + emlen - flen - mdlen, from, (unsigned int)flen);
      if (RAND_bytes(seed, mdlen) <= 0)
          return 0;
  #ifdef PKCS_TESTVECT
      memcpy(seed,
             "\xaa\xfd\x12\xf6\x59\xca\xe6\x34\x89\xb4\x79\xe5\x07\x6d\xde\xc2\xf0\x6c\xb5\x8f",
             20);
  #endif
  
      dbmask = OPENSSL_malloc(emlen - mdlen);
      if (dbmask == NULL) {
          RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
          return 0;
      }
  
      if (PKCS1_MGF1(dbmask, emlen - mdlen, seed, mdlen, mgf1md) < 0)
          return 0;
      for (i = 0; i < emlen - mdlen; i++)
          db[i] ^= dbmask[i];
  
      if (PKCS1_MGF1(seedmask, mdlen, db, emlen - mdlen, mgf1md) < 0)
          return 0;
      for (i = 0; i < mdlen; i++)
          seed[i] ^= seedmask[i];
  
      OPENSSL_free(dbmask);
      return 1;
  }
  
  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, mlen = -1, one_index = 0, msg_index;
      unsigned int good, found_one_byte;
      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)
          md = EVP_sha1();
      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)
          goto decoding_err;
  
      dblen = num - mdlen - 1;
      db = OPENSSL_malloc(dblen);
      em = OPENSSL_malloc(num);
      if (db == NULL || em == NULL) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, ERR_R_MALLOC_FAILURE);
          goto cleanup;
      }
  
      /*
       * Always do this zero-padding copy (even when num == flen) to avoid
       * leaking that information. The copy still leaks some side-channel
       * information, but it's impossible to have a fixed  memory access
       * pattern since we can't read out of the bounds of |from|.
       *
       * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
       */
      memset(em, 0, num);
      memcpy(em + num - flen, from, flen);
  
      /*
       * 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.
       */
      if (!good)
          goto decoding_err;
  
      msg_index = one_index + 1;
      mlen = dblen - msg_index;
  
      if (tlen < mlen) {
          RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1, RSA_R_DATA_TOO_LARGE);
          mlen = -1;
      } else {
          memcpy(to, db + msg_index, mlen);
          goto cleanup;
      }
  
   decoding_err:
      /*
       * To avoid chosen ciphertext attacks, the error message should not
       * reveal which kind of decoding error happened.
       */
      RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_OAEP_MGF1,
             RSA_R_OAEP_DECODING_ERROR);
   cleanup:
      OPENSSL_free(db);
      OPENSSL_free(em);
      return mlen;
  }
  
  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;
      for (i = 0; outlen < len; i++) {
          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);
          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:
      EVP_MD_CTX_free(c);
      return rv;
  }
  