Question

I am updating my helper functions library. I am wondering whether it is too much of salt in the password encryption?

Is there any difference between:

mb_substr(sha1($str . AY_HASH), 5, 10) . mb_substr(sha1(AY_HASH . sha1($str . AY_HASH)), 5, 10) . mb_substr(md5($str . AY_HASH), 5, 10)

and simply:

sha1(AY_HASH . sha1($str . AY_HASH))

AY_HASH being the salt. Which should I prefer and if neither is good, what is the best alternative?

Answer 1

A salt should be generated for each password, not a secret string used on every password. Re-using a salt means that the attacker will only need to create one rainbow table for every password instead of one per password.

I invite you to read a previous answer I wrote on secure hashing. The rules are simple:

• Do NOT use a single salt for all passwords. Use a randomly generated salt per password.
• Do NOT rehash an unmodified hash (collision issue, see my previous answer, you need infinite input for hashing).
• Do NOT attempt to create your own hashing algorithm or mix-matching algorithms into a complex operation.
• If stuck with broken/unsecure/fast hash primitives, use key strengthening. This increases the time required for the attacker to compute a rainbow table. Example:

---

function strong_hash($input, $salt = null, $algo = 'sha512', $rounds = 20000) {
  if($salt === null) {
    $salt = crypto_random_bytes(16);
  } else {
    $salt = pack('H*', substr($salt, 0, 32));
  }

  $hash = hash($algo, $salt . $input);

  for($i = 0; $i < $rounds; $i++) {
    // $input is appended to $hash in order to create
    // infinite input.
    $hash = hash($algo, $hash . $input);
  }

  // Return salt and hash. To verify, simply
  // passed stored hash as second parameter.
  return bin2hex($salt) . $hash;
}

function crypto_random_bytes($count) {
  static $randomState = null;

  $bytes = '';

  if(function_exists('openssl_random_pseudo_bytes') &&
      (strtoupper(substr(PHP_OS, 0, 3)) !== 'WIN')) { // OpenSSL slow on Win
    $bytes = openssl_random_pseudo_bytes($count);
  }

  if($bytes === '' && is_readable('/dev/urandom') &&
     ($hRand = @fopen('/dev/urandom', 'rb')) !== FALSE) {
    $bytes = fread($hRand, $count);
    fclose($hRand);
  }

  if(strlen($bytes) < $count) {
    $bytes = '';

    if($randomState === null) {
      $randomState = microtime();
      if(function_exists('getmypid')) {
        $randomState .= getmypid();
      }
    }

    for($i = 0; $i < $count; $i += 16) {
      $randomState = md5(microtime() . $randomState);

      if (PHP_VERSION >= '5') {
        $bytes .= md5($randomState, true);
      } else {
        $bytes .= pack('H*', md5($randomState));
      }
    }

    $bytes = substr($bytes, 0, $count);
  }

  return $bytes;
}

---

If anything however, you should use bcrypt, which is future-adaptable. Again, I invite you to my previous answer for a more detailed example.