public class MD5 {         static List<KeyValuePair<char, char>> MappingList;         #region 加密      public static string Encrypt(string str)         /// <summary>         /// 加密         /// </summary>         /// <param name="str">要加密的字符串</param>         /// <returns>返回结果的字符串</returns>         public static string Encrypt(string str)         {             MappingList = new List<KeyValuePair<char, char>>();             for (char c = '0'; c <= '9'; c++)                 MappingList.Add(new KeyValuePair<char, char>(c, (char)(c - '0' + 'a')));             for (char c = 'a'; c <= 'f'; c++)                 MappingList.Add(new KeyValuePair<char, char>(c, (char)(c - 'a' + 'u')));             return Encoding.ASCII.GetBytes(str)                 .Select((b, i) => (b ^ ((byte)(0xa0 + i))).ToString("x2"))                 .Aggregate("", (s, c) => s + c)                 .ToCharArray().Select(c => MappingList.First(kv => kv.Key == c).Value)                 .Aggregate("", (s, c) => s + c);         }         #endregion         #region 解密       public static string Decrypt(string str)         /// <summary>         /// 解密         /// </summary>         /// <param name="str">解密的字符串</param>         /// <returns>返回结果字符串</returns>         public static string Decrypt(string str)         {             string base16 = str.ToCharArray()                 .Select(c => MappingList.First(kv => kv.Value == c).Key)                 .Aggregate("", (s, c) => s + c);             return Encoding.ASCII.GetString((new byte[base16.Length / 2])                 .Select((b, i) => (byte)(Convert.ToByte(base16.Substring(i * 2, 2), 16) ^ ((byte)(0xa0 + i)))).ToArray());         }         #endregion }