gistfile1.txt

```  
  
  private readonly AesCryptoServiceProvider AES = new AesCryptoServiceProvider();
        public CryptClass(string EncryptKey)
        {
            // Initialize the crypto provider.
            AES.Mode = CipherMode.ECB;
            AES.Key = TruncateHash(EncryptKey, AES.KeySize / 8);
            AES.IV = TruncateHash("", AES.BlockSize / 8);
            AES.Padding = PaddingMode.PKCS7;
        }
        public string Encrypt(string plaintext)
        {
            plaintext += "." + DateTime.Now.AddMinutes(5.0).Ticks.ToString();
            plaintext += "." + GetStringHash(plaintext);
            Debug.WriteLine(plaintext);
            // Convert the plaintext string to a byte array.
            byte[] plaintextBytes = System.Text.Encoding.Unicode.GetBytes(plaintext);
            // Create the stream.
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            // Create the encoder to write to the stream.
            CryptoStream encStream = new CryptoStream(ms, AES.CreateEncryptor(), CryptoStreamMode.Write);
            // Use the crypto stream to write the byte array to the stream.
            encStream.Write(plaintextBytes, 0, plaintextBytes.Length);
            encStream.FlushFinalBlock();
            // Convert the encrypted stream to a printable string.
            return Convert.ToBase64String(ms.ToArray());
        }
        public string Decrypt(string encryptedtext)
        {
            return Decrypt(encryptedtext, false);
        }
        /// <summary>
        /// Decrypts the specified encryptedtext.
        /// </summary>
        /// <param name="encryptedtext">The encryptedtext.</param>
        /// <param name="b24">if set to <c>true</c> add 24 hours of validity for the token.</param>
        /// <returns></returns>
        /// <exception cref="System.Exception">
        /// Invalid hash !!!!
        /// or
        /// This Token is no longer valid !!!!
        /// </exception>
        public string Decrypt(string encryptedtext, bool b24 = false)
        {
            // Convert the encrypted text string to a byte array.
            byte[] encryptedBytes = Convert.FromBase64String(encryptedtext);
            // Create the stream.
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            // Create the decoder to write to the stream.
            CryptoStream decStream = new CryptoStream(ms, AES.CreateDecryptor(), CryptoStreamMode.Write);
            // Use the crypto stream to write the byte array to the stream.
            decStream.Write(encryptedBytes, 0, encryptedBytes.Length);
            decStream.FlushFinalBlock();
            // Convert the plaintext stream to a string.
            string plaintext = System.Text.Encoding.Unicode.GetString(ms.ToArray());
            // 
            int idx = plaintext.LastIndexOf(".");
            string hash = plaintext.Substring(idx + 1);
            plaintext = plaintext.Substring(0, idx);
            if (hash != GetStringHash(plaintext))
            {
                throw new Exception("Invalid hash !!!!");
            }
            idx = plaintext.LastIndexOf(".");
            string ValidityEndDate = plaintext.Substring(idx + 1);
            DateTime dtEnd = new System.DateTime(long.Parse(ValidityEndDate));
            if (b24) { dtEnd = dtEnd.AddDays(1.0); }
            if (dtEnd < System.DateTime.Now) { throw new Exception("This Token is no longer valid !!!!"); }
            plaintext = plaintext.Substring(0, idx);
            return plaintext;
        }
        private byte[] TruncateHash(string key, int length)
        {
            byte[] hash = GetHash(key);
            // Truncate or pad the hash.
            Array.Resize(ref hash, length);
            return hash;
        }
        private byte[] GetHash(string key)
        {
            byte[] keyBytes = System.Text.Encoding.ASCII.GetBytes(key);
            return keyBytes;
        }
        private string GetStringHash(string key)
        {
            string retHash = Convert.ToBase64String(GetHash(key));
            return retHash;
        }
        ```