Easy way to encrypt/obfuscate a byte array using a secret in .NET?

Question

I'm looking for a way to encrypt/obfuscate (and of course decrypt/deobfuscate) an array of byte using .NET 3.5.

Basically:

byte[] aMixedUp = Encrypt(aMyByteData, "THIS IS THE SECRET KEY USED TO ENCRYPT");

and on the other side:

byte[] aDecrypted = Decrypt(aMixedUp, "THIS IS THE SECRET KEY USED TO ENCRYPT");

It does not have to be bullet proof. The idea is just to prevent users from directly seeing what's in the bytes in case they map to ASCII but it should be better then ROT13.

Is there something in the .NET libraries I can easily use?

Answer 1

Here's some code I wrote to encrypt/decrypt a string. The encrypted string is Base64 encoded for ease of serialization to XML, etc. You could easily convert this code to work directly with byte arrays instead of strings.

/// <summary>
/// Create and initialize a crypto algorithm.
/// </summary>
/// <param name="password">The password.</param>
private static SymmetricAlgorithm GetAlgorithm(string password)
{
    var algorithm = Rijndael.Create();
    var rdb = new Rfc2898DeriveBytes(password, new byte[] {
        0x53,0x6f,0x64,0x69,0x75,0x6d,0x20,             // salty goodness
        0x43,0x68,0x6c,0x6f,0x72,0x69,0x64,0x65
    });
    algorithm.Padding = PaddingMode.ISO10126;
    algorithm.Key = rdb.GetBytes(32);
    algorithm.IV = rdb.GetBytes(16);
    return algorithm;
}


/// <summary>
/// Encrypts a string with a given password.
/// </summary>
/// <param name="clearText">The clear text.</param>
/// <param name="password">The password.</param>
public static string EncryptString(string clearText, string password)
{
    var algorithm = GetAlgorithm(password);
    var encryptor = algorithm.CreateEncryptor();
    var clearBytes = Encoding.Unicode.GetBytes(clearText);
    using (var ms = new MemoryStream())
    using (var cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
    {
        cs.Write(clearBytes, 0, clearBytes.Length);
        cs.Close();
        return Convert.ToBase64String(ms.ToArray());
    }
}

/// <summary>
/// Decrypts a string using a given password.
/// </summary>
/// <param name="cipherText">The cipher text.</param>
/// <param name="password">The password.</param>
public static string DecryptString(string cipherText, string password)
{
    var algorithm = GetAlgorithm(password);
    var decryptor = algorithm.CreateDecryptor();
    var cipherBytes = Convert.FromBase64String(cipherText);
    using (var ms = new MemoryStream())
    using (var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Write))
    {
        cs.Write(cipherBytes, 0, cipherBytes.Length);
        cs.Close();
        return Encoding.Unicode.GetString(ms.ToArray());
    }
}