Wednesday, July 9, 2014

Encryption and Decryption in C#

Encryption is used to transform a data into some un-readable form so that authenticated person only can read/access the data. It requires some secret information to transform the plain text to cipher text; it is usually referred as key.
There are many modern cryptographic methods used for encryption and decryption and it is classified in to two classes of key based algorithms.
1.       Symmetric Algorithm
a.        Same key is used for both Encryption and Decryption. The key will be kept as secret.
b.       Symmetric Ciphers is divided into Stream and Block Ciphers.
                                                               i.      Stream Ciphers – It encrypts a single bit of plain text at a time.
                                                             ii.      Block Ciphers –    It takes number of bits and encrypts them as a single unit.
2.       Asymmetric Algorithm
a.       Different key is used for Encryption and Decryption. It is also called as public Key algorithm.
b.      Encryption key is public and the Decryption key will be kept as secret.
c.       By using this asymmetric algorithm, anyone can encrypt the message by using encryption key but the message can be decrypted only by using decryption key.
3.       Hybrid Encryption – Symmetric and Asymmetric algorithm are used together and it is called as Hybrid Encryption.
  Algorithm Requirements:
1.       The Key will be kept secret and should be Random.
2.       It should not be possible to find the key even if the plain text and Cipher text are known.

  Types of Symmetric Encryption Algorithm:
1.       Data Encryption Standard (DES)
2.       Blow Fish
3.       Triple DES (3DES)
4.       Advanced Encryption Standard (AES)
  Below is the example for encryption and decryption in C# using Triple DES algorithm.
 Public class Program
    {
        static void Main(string[] args)
        {
            var text = "This is Plain Text";

            var encryptedText = CryptoGraphyExample.EncryptPlainTextToCipherText(text);
            var decryptedText = CryptoGraphyExample.DecryptCipherTextToPlainText(encryptedText);

            Console.WriteLine("Passed Text = " + text);
            Console.WriteLine("EncryptedText = " + encryptedText);
            Console.WriteLine("DecryptedText = " + decryptedText);

            Console.ReadLine();
        }
    }

public class CryptoGraphyExample
    {
        /// <summary>
        /// This security key should be very complex and Random for encrypting the text. This playing vital role in encrypting the text.
        /// </summary>
        private const string _securityKey = "MyComplexKey";


        /// <summary>
        /// This method is used to convert the plain text to Encrypted/Un-Readable Text format.
        /// </summary>
        /// <param name="PlainText">Plain Text to Encrypt before transferring over the network.</param>
        /// <returns>Cipher Text</returns>
        public static string EncryptPlainTextToCipherText(string PlainText)
        {
            //Getting the bytes of Input String.
            byte[] toEncryptedArray = UTF8Encoding.UTF8.GetBytes(PlainText);

            MD5CryptoServiceProvider objMD5CryptoService = new MD5CryptoServiceProvider();

            //Gettting the bytes from the Security Key and Passing it to compute the Corresponding Hash Value.
            byte[] securityKeyArray = objMD5CryptoService.ComputeHash(UTF8Encoding.UTF8.GetBytes(_securityKey));

            //De-allocatinng the memory after doing the Job.
            objMD5CryptoService.Clear();

            var objTripleDESCryptoService = new TripleDESCryptoServiceProvider();

            //Assigning the Security key to the TripleDES Service Provider.
            objTripleDESCryptoService.Key = securityKeyArray;

            //Mode of the Crypto service is Electronic Code Book.
            objTripleDESCryptoService.Mode = CipherMode.ECB;

            //Padding Mode is PKCS7 if there is any extra byte is added.
            objTripleDESCryptoService.Padding = PaddingMode.PKCS7;

            var objCrytpoTransform = objTripleDESCryptoService.CreateEncryptor();

            //Transform the bytes array to resultArray
            byte[] resultArray = objCrytpoTransform.TransformFinalBlock(toEncryptedArray, 0, toEncryptedArray.Length);

            //Releasing the Memory Occupied by TripleDES Service Provider for Encryption.
            objTripleDESCryptoService.Clear();

            //Convert and return the encrypted data/byte into string format.
            return Convert.ToBase64String(resultArray, 0, resultArray.Length);
        }


        /// <summary>
        /// This method is used to convert the Cipher/Encypted text to Plain Text.
        /// </summary>
        /// <param name="CipherText">Encrypted Text</param>
        /// <returns>Plain/Decrypted Text</returns>
        public static string DecryptCipherTextToPlainText(string CipherText)
        {
            byte[] toEncryptArray = Convert.FromBase64String(CipherText);

            MD5CryptoServiceProvider objMD5CryptoService = new MD5CryptoServiceProvider();

            //Gettting the bytes from the Security Key and Passing it to compute the Corresponding Hash Value.
            byte[] securityKeyArray = objMD5CryptoService.ComputeHash(UTF8Encoding.UTF8.GetBytes(_securityKey));

            //De-allocatinng the memory after doing the Job.
            objMD5CryptoService.Clear();

            var objTripleDESCryptoService = new TripleDESCryptoServiceProvider();

            //Assigning the Security key to the TripleDES Service Provider.
            objTripleDESCryptoService.Key = securityKeyArray;
           
            //Mode of the Crypto service is Electronic Code Book.
            objTripleDESCryptoService.Mode = CipherMode.ECB;

            //Padding Mode is PKCS7 if there is any extra byte is added.
            objTripleDESCryptoService.Padding = PaddingMode.PKCS7;

            var objCrytpoTransform = objTripleDESCryptoService.CreateDecryptor();

            //Transform the bytes array to resultArray
            byte[] resultArray = objCrytpoTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);

            //Releasing the Memory Occupied by TripleDES Service Provider for Decryption.          
            objTripleDESCryptoService.Clear();

            //Convert and return the decrypted data/byte into string format.
            return UTF8Encoding.UTF8.GetString(resultArray);
        }
    }