php encryption and decryption processing class

class SysCrypt {

private $crypt_key;

// 构造函数
public function __construct($crypt_key) {
   $this -> crypt_key = $crypt_key;
}

public function php_encrypt($txt) {
   srand((double)microtime() * 1000000);
   $encrypt_key = md5(rand(0,32000));
   $ctr = 0;
   $tmp = '';
   for($i = 0;$i    $ctr = $ctr == strlen($encrypt_key) ? 0 : $ctr;
    $tmp .= $encrypt_key[$ctr].($txt[$i]^$encrypt_key[$ctr++]);
   }
   return base64_encode(self::__key($tmp,$this -> crypt_key));
}

public function php_decrypt($txt) {
   $txt = self::__key(base64_decode($txt),$this -> crypt_key);
   $tmp = '';
   for($i = 0;$i < strlen($txt); $i++) {
    $md5 = $txt[$i];
    $tmp .= $txt[++$i] ^ $md5;
   }
   return $tmp;
}

private function __key($txt,$encrypt_key) {
   $encrypt_key = md5($encrypt_key);
   $ctr = 0;
   $tmp = '';
   for($i = 0; $i < strlen($txt); $i++) {
    $ctr = $ctr == strlen($encrypt_key) ? 0 : $ctr;
    $tmp .= $txt[$i] ^ $encrypt_key[$ctr++];
   }
   return $tmp;
}

public function __destruct() {
   $this -> crypt_key = null;
}
}


$sc = new SysCrypt('phpwms');
$text = '110';
print($sc -> php_encrypt($text));
print('');
print($sc -> php_decrypt($sc -> php_encrypt($text)));
?>

加密解密, php