public class Base64
    {
        ///编码  code_type  编码方式(UTF-8),code 编码内容
        public static string EncodeBase64(string code_type, string code)
        {
            string encode = "";
            byte[] bytes = Encoding.GetEncoding(code_type).GetBytes(code);
            try
            {
                encode = Convert.ToBase64String(bytes);
            }
            catch
            {
                encode = code;
            }
            return encode;
        }
        ///解码  code_type  编码方式(UTF-8),code  解码内容
        public static string DecodeBase64(string code_type, string code)
        {
            string decode = "";
            byte[] bytes = Convert.FromBase64String(code);
            try
            {
                decode = Encoding.GetEncoding(code_type).GetString(bytes);
            }
            catch
            {
                decode = code;
            }
            return decode;
        }
    }
原文:https://www.cnblogs.com/AbelAngelo/p/13228566.html