Michael E. Chancey Jr.

String Encryption and Decryption Extension

// December 10th, 2009 // Useful Code

This extension is a little longer then usual and it also has a few supporting extensions which are required to make it run; I have included all of which in this post. I wrote a few extras to just make some of the code a little bit shorter and neater. The first is Reverse which like the name implies reverses an incoming string. The second is ToByteArray which converts a string to a Byte Array. The third is ConvertToString which does the exact opposite of ToByteArray by converting a Byte Array back into a string.

//Code

---

        /// <summary>
        /// ENCRYPTS A STRING USING AES ENCRYPTION AND A PASSWORD
        /// </summary>
        /// <param name="s">INCOMING STRING TO ENCRYPT</param>
        /// <param name="password">PASSWORD TO USE FOR ENCRYPTION</param>
        /// <returns>BASE64 ENCODED ENCRYPTED STRING</returns>
        public static string EncryptString(this string s, string password)
        {
            //CREATE AN AES CRYPTOGRAPHY CLASS
            using (Aes tmpAes = AesCryptoServiceProvider.Create())
            {
                //CREATE A PASSWORD DERIVED BYTES CLASS TO CONVERT A SIMPLE PASSWORD INTO SOMETHING MORE COMPLEX
                PasswordDeriveBytes tmpPasswordBytes = new PasswordDeriveBytes(password.ToByteArray(), password.Reverse().ToByteArray());

                //CREATE A ICRYPTO TRANSFORM PROVIDER USING 256 BITS FOR THE KEY WHICH IS DERIVED FROM THE PASSWORD PASSED IN
                using (ICryptoTransform tmpCrypto = tmpAes.CreateEncryptor(tmpPasswordBytes.GetBytes(256 / 8), tmpPasswordBytes.GetBytes(16)))
                {
                    //CREATE A TEMPORARY MEMORY STREAM TO HOLD THE DATA WHICH IS BEING ENCRYPTED
                    using (MemoryStream tmpMemoryStream = new MemoryStream())
                    {
                        //CREATE THE CRYPTO STREAM WHICH WILL WRITE TO THE UNDERLYING MEMORY STREAM
                        using (CryptoStream tmpStream = new CryptoStream(tmpMemoryStream, tmpCrypto, CryptoStreamMode.Write))
                        {
                            tmpStream.Write(s.ToByteArray(), 0, s.Length);
                            tmpStream.Flush();
                        }

                        //CONVERT THE DATA TO A BASE64 STRING SO WE HAVE ALL VALID CHARACTERS IN THE STRING
                        return Convert.ToBase64String(tmpMemoryStream.ToArray());
                    }
                }
            }
        }

        /// <summary>
        /// DECRYPTS A BASE64 ENCODED STRING USING AES AND PASSWORD
        /// </summary>
        /// <param name="s">INCOMING BASE64 ENCODED STRING TO DECRYPT</param>
        /// <param name="password">PASSWORD USED DURING THE ENCRYPTION PROCESS TO REVERSE THE SEQUENCE</param>
        /// <returns>ORIGINAL STRING PRIOR TO ENCRYPTION</returns>
        public static string DecryptString(this string s, string password)
        {
            //CREATE AN AES CRYPTOGRAPHY CLASS
            using (Aes tmpAes = AesCryptoServiceProvider.Create())
            {
                //CREATE A PASSWORD DERIVED BYTES CLASS TO CONVERT A SIMPLE PASSWORD INTO SOMETHING MORE COMPLEX
                PasswordDeriveBytes tmpPasswordBytes = new PasswordDeriveBytes(password.ToByteArray(), password.Reverse().ToByteArray());

                //CREATE A ICRYPTO TRANSFORM PROVIDER USING 256 BITS FOR THE KEY WHICH IS DERIVED FROM THE PASSWORD PASSED IN
                using (ICryptoTransform tmpCrypto = tmpAes.CreateDecryptor(tmpPasswordBytes.GetBytes(256 / 8), tmpPasswordBytes.GetBytes(16)))
                {
                    //CREATE A MEMORY STREAM FROM THE BASE64 STRING WHICH IS BEING PASSED IN
                    using (MemoryStream tmpMemoryStream = new MemoryStream(Convert.FromBase64String(s)))
                    {
                        //CREATE A NEW STREAM WHICH WILL DECRYPT THE DATA AS WE READ IT
                        using (CryptoStream tmpStream = new CryptoStream(tmpMemoryStream, tmpCrypto, CryptoStreamMode.Read))
                        {
                            int readCount;
                            byte[] tmpBuffer = new byte[1024];
                            StringBuilder tmpReturn = new StringBuilder();

                            //CATCH THE ERROR INCASE THE PASSWORD IS INVALID
                            try
                            {
                                //AS LONG AS THEIR IS DATA ON THE STREAM KEEP READING
                                while ((readCount = tmpStream.Read(tmpBuffer, 0, tmpBuffer.Length)) != 0)
                                {
                                    tmpReturn.Append(tmpBuffer.Take(readCount).ToArray().ConvertToString());
                                }

                                //RETURN THE DECRYPTED STRING VALUE
                                return tmpReturn.ToString();
                            }
                            catch (CryptographicException ex)
                            {
                                return "";
                            }
                        }
                    }
                }
            }
        }

        #region "Supporting Extensions"
        /// <summary>
        /// CONVERT AN ARRAY OF BYTES INTO THE UTF8 STRING
        /// </summary>
        /// <param name="b">ARRAY OF BYTES COMING IN</param>
        /// <returns>STRING REPRESENTATION OF THE BYTES PASSED IN</returns>
        public static string ConvertToString(this byte[] b)
        {
            return System.Text.ASCIIEncoding.UTF8.GetString(b);
        }

        /// <summary>
        /// REVERSES A STRING
        /// </summary>
        /// <param name="s">INCOMING STRING TO REVERSE</param>
        /// <returns>REVERSED STRING</returns>
        public static string Reverse(this string s)
        {
            StringBuilder tmpReturn = new StringBuilder();

            //LOOP THROUGH EACH CHARACTER FROM BACK TO FRONT AND INSERT IT INTO THE BUILDER
            for (int i = s.Length - 1; i >= 0; i--)
                tmpReturn.Append(s[i]);

            //RETURN THE REVERSED STRING TO THE CALLING FUNCTION
            return tmpReturn.ToString();
        }

        /// <summary>
        /// CONVERTS A STRING INTO UTF8 ENCODED BYTE ARRAY
        /// </summary>
        /// <param name="s">INCOMING STRING TO CONVERT</param>
        /// <returns>BYTE ARRAY OF THE INCOMING STRING</returns>
        public static byte[] ToByteArray(this string s)
        {
            //CONVERT THE STRING TO A BYTE ARRAY
            return System.Text.ASCIIEncoding.UTF8.GetBytes(s);
        }
        #endregion

//Usage

---

    class Program
    {
        static void Main(string[] args)
        {
            string tmpEnc = "Hello, World!".EncryptString("password");
            string tmpDec = tmpEnc.DecryptString("password");

            Console.WriteLine("{0}\n{1}", tmpEnc, tmpDec);
            Console.ReadLine();
        }
    }