Symmetric encrypt/decrypt in .NET

Question

I am after a symmetric encryption/decryption routine in C#. I know there have been a few questions on this topic before, but most of the answers seem to be about the philosophy of encryption rather than giving actual code.

Update: I'd really like to see some code, rather than just links. Many thanks!

Answer 1

Look at the example code at the bottom of this page.

Copy-pasting it here:

int Rfc2898KeygenIterations= 100;
int AesKeySizeInBits = 128;
String Password = "VerySecret!";
byte[] Salt = new byte[16];
System.Random rnd = new System.Random(); 
rnd.NextBytes(Salt);
byte[] rawPlaintext = System.Text.Encoding.Unicode.GetBytes("This is all clear now!");
byte[] cipherText= null;
byte[] plainText= null;
using (Aes aes = new AesManaged())
{
    aes.Padding = PaddingMode.PKCS7;
    aes.KeySize = AesKeySizeInBits;
    int KeyStrengthInBytes= aes.KeySize/8;
    System.Security.Cryptography.Rfc2898DeriveBytes rfc2898 =
        new System.Security.Cryptography.Rfc2898DeriveBytes(Password, Salt, Rfc2898KeygenIterations);
    aes.Key = rfc2898.GetBytes(KeyStrengthInBytes);
    aes.IV = rfc2898.GetBytes(KeyStrengthInBytes);
    using (MemoryStream ms = new MemoryStream())
    {
        using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
        {
            cs.Write(rawPlaintext, 0, rawPlaintext.Length);
        }
        cipherText= ms.ToArray();
    }

    using (MemoryStream ms = new MemoryStream())
    {
        using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
        {
            cs.Write(cipherText, 0, cipherText.Length);
        }
        plainText = ms.ToArray();
    }
}
string s = System.Text.Encoding.Unicode.GetString(plainText);
Console.WriteLine(s);

Answer 2

Here's a simple solution that I found on a VB.NET forum and converted to C#. It certainly helped me understand the topic better.

// Shamelessly lifted from http://discuss.itacumens.com/index.php?topic=62872.0, 
// then converted to C# (http://www.developerfusion.com/tools/convert/vb-to-csharp/) and
// changed where necessary.
public class Encryptor
{
    private static SymmetricAlgorithm _cryptoService = new TripleDESCryptoServiceProvider(); 
    // maybe use AesCryptoServiceProvider instead?

    // vector and key have to match between encryption and decryption
    public static string Encrypt(string text, byte[] key, byte[] vector)
    {
        return Transform(text, _cryptoService.CreateEncryptor(key, vector));
    }

    // vector and key have to match between encryption and decryption
    public static string Decrypt(string text, byte[] key, byte[] vector)
    {
        return Transform(text, _cryptoService.CreateDecryptor(key, vector));
    }

    private static string Transform(string text, ICryptoTransform cryptoTransform)
    {
        MemoryStream stream = new MemoryStream();
        CryptoStream cryptoStream = new CryptoStream(stream, cryptoTransform, CryptoStreamMode.Write);

        byte[] input = Encoding.Default.GetBytes(text);

        cryptoStream.Write(input, 0, input.Length);
        cryptoStream.FlushFinalBlock();

        return Encoding.Default.GetString(stream.ToArray());
    }
}