using System;

using System.Text;

using System.Security.Cryptography;

using System.IO;

​

public class Program

{

    public static void Main()

    {

        string pw = "sdfsdf";

        string data = Encrypt("dsfsdf", pw);

        Console.WriteLine("Encrypted: " + data);

        Console.WriteLine("Decrypted: " + Decrypt(data, pw));

    }

​

    // This constant string is used as a "salt" value for the PasswordDeriveBytes function calls.

    // This size of the IV (in bytes) must = (keysize / 8).  Default keysize is 256, so the IV must be

    // 32 bytes long.  Using a 16 character string here gives us 32 bytes when converted to a byte array.

    // ^ all of that is completely wrong.

    // 16 Characters in ascii is 16 bytes. Each character is 1 byte in ASCII. 

    // our "initvector" is used in our AES (Rijndael) encryption function only. 

    // it also shouldn't have been a constant variable but hey who needs security anyways.

    private const string initVector = "h7g3e4m3t5st5zjw";

    // This constant is used to determine the keysize of the encryption algorithm.

    private const int keysize = 256;

    public static string Encrypt(string plainText, string passPhrase)

    {

        byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);

        byte[] plainTextBytes = Encoding.UTF8.GetBytes(plainText);

        Console.WriteLine("IV Byte Array: " + BitConverter.ToString(initVectorBytes).Replace("-", " ") + " (Size: " + initVectorBytes.Length.ToString() + ")");

        var password = new PasswordDeriveBytes(passPhrase, null);

        byte[] keyBytes = password.GetBytes(keysize / 8);

        var symmetricKey = new RijndaelManaged();

        symmetricKey.Mode = CipherMode.CBC;

        Console.WriteLine("Blocksize: " + symmetricKey.BlockSize.ToString() + "-Bit");

        var encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);

        var memoryStream = new MemoryStream();

        var cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);

        cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);

        cryptoStream.FlushFinalBlock();

        byte[] cipherTextBytes = memoryStream.ToArray();

        memoryStream.Close();

        cryptoStream.Close();

        return Convert.ToBase64String(cipherTextBytes);

    }

​

    public static string Decrypt(string cipherText, string passPhrase)

    {

        byte[] initVectorBytes = Encoding.ASCII.GetBytes(initVector);

        byte[] cipherTextBytes = Convert.FromBase64String(cipherText);

        var password = new PasswordDeriveBytes(passPhrase, null);

        byte[] keyBytes = password.GetBytes(keysize / 8);

        var symmetricKey = new RijndaelManaged();

        symmetricKey.Mode = CipherMode.CBC;

        var decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);

        var memoryStream = new MemoryStream(cipherTextBytes);

        var cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);

        byte[] plainTextBytes = new byte[cipherTextBytes.Length];

        int decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

        memoryStream.Close();

        cryptoStream.Close();

        return Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);

    }

}