/// <summary>
    /// 將字符串使用base64算法加密
    /// </summary>
    /// <param name="code_type">編碼類型（編碼名稱）
    /// * 代碼頁 名稱
    /// * 1200 "UTF-16LE"、"utf-16"、"ucs-2"、"unicode"或"ISO-10646-UCS-2"
    /// * 1201 "UTF-16BE"或"unicodeFFFE"
    /// * 1252 "windows-1252"
    /// * 65000 "utf-7"、"csUnicode11UTF7"、"unicode-1-1-utf-7"、"unicode-2-0-utf-7"、"x-unicode-1-1-utf-7"或"x-unicode-2-0-utf-7"
    /// * 65001 "utf-8"、"unicode-1-1-utf-8"、"unicode-2-0-utf-8"、"x-unicode-1-1-utf-8"或"x-unicode-2-0-utf-8"
    /// * 20127 "us-ascii"、"us"、"ascii"、"ANSI_X3.4-1968"、"ANSI_X3.4-1986"、"cp367"、"csASCII"、"IBM367"、"iso-ir-6"、"ISO646-US"或"ISO_646.irv:1991"
    /// * 54936 "GB18030"   
    /// </param>
    /// <param name="code">待加密的字符串</param>
    /// <returns>加密后的字符串</returns>
    public string EncodeBase64(string code_type, string code)
    {
        string encode = "";
        byte[] bytes = Encoding.GetEncoding(code_type).GetBytes(code);  //將一組字符編碼為一個字節序列.
        try
        {
            encode = Convert.ToBase64String(bytes);  //將8位無符號整數數組的子集轉換為其等效的,以64為基的數字編碼的字符串形式.
        }
        catch
        {
            encode = code;
        }
        return encode;
    }

/// <summary>
    /// 將字符串使用base64算法解密
    /// </summary>
    /// <param name="code_type">編碼類型</param>
    /// <param name="code">已用base64算法加密的字符串</param>
    /// <returns>解密后的字符串</returns>
    public string DecodeBase64(string code_type, string code)
    {
        string decode = "";
        byte[] bytes = Convert.FromBase64String(code);  //將2進制編碼轉換為8位無符號整數數組.
        try
        {
            decode = Encoding.GetEncoding(code_type).GetString(bytes);  //將指定字節數組中的一個字節序列解碼為一個字符串。
        }
        catch
        {
            decode = code;
        }
        return decode;
    }