html符号化と復号化

public static string EncodeStr(string str)
        {
            str = Regex.Replace(str, @"<html[^>]*?>.*?</html>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<html[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<body[^>]*?>.*?</body>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<body[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<meta[^>]*?>.*?</meta>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<meta[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<frame[^>]*?>.*?</frame>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<frame[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<frameset[^>]*?>.*?</frameset>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<frameset[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<iframe[^>]*?>.*?</iframe>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<iframe[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<layer[^>]*?>.*?</layer>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<layer[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<ilayer[^>]*?>.*?</ilayer>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<ilayer[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<applet[^>]*?>.*?</applet>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<applet[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<script[^>]*?>.*?</script>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<script[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<link[^>]*?>.*?</link>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<link[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<style[^>]*?>.*?</style>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<style[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<form[^>]*?>.*?</form>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<form[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<input[^>]*?>.*?</input>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<input[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<textarea[^>]*?>.*?</textarea>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<textarea[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<select[^>]*?>.*?</select>", "",
            RegexOptions.IgnoreCase);
            str = Regex.Replace(str, @"<select[^>]*?/>", "",
            RegexOptions.IgnoreCase);
            return HttpUtility.HtmlEncode(str);
        }
        public static string DecodeStr(string encodeStr)
        {
            return HttpUtility.HtmlDecode(encodeStr);
        }