Simple insecure two-way data “obfuscation”?

Question

I\'m looking for very simple obfuscation (like encrypt and decrypt but not necessarily secure) functionality for some data. It\'s not mission critical. I need something to k

Answer 1

I combined what I found the best from several answers and comments.

• Random initialization vector prepended to crypto text (@jbtule)
• Use TransformFinalBlock() instead of MemoryStream (@RenniePet)
• No pre-filled keys to avoid anyone copy & pasting a disaster
• Proper dispose and using patterns

Code:

/// 

/// Simple encryption/decryption using a random initialization vector
/// and prepending it to the crypto text.
/// 
/// Based on multiple answers in http://stackoverflow.com/questions/165808/simple-two-way-encryption-for-c-sharp 
public class SimpleAes : IDisposable
{
    /// 

    ///     Initialization vector length in bytes.
    /// 
    private const int IvBytes = 16;

    /// 

    ///     Must be exactly 16, 24 or 32 bytes long.
    /// 
    private static readonly byte[] Key = Convert.FromBase64String("FILL ME WITH 24 (2 pad chars), 32 OR 44 (1 pad char) RANDOM CHARS"); // Base64 has a blowup of four-thirds (33%)

    private readonly UTF8Encoding _encoder;
    private readonly ICryptoTransform _encryptor;
    private readonly RijndaelManaged _rijndael;

    public SimpleAes()
    {
        _rijndael = new RijndaelManaged {Key = Key};
        _rijndael.GenerateIV();
        _encryptor = _rijndael.CreateEncryptor();
        _encoder = new UTF8Encoding();
    }

    public string Decrypt(string encrypted)
    {
        return _encoder.GetString(Decrypt(Convert.FromBase64String(encrypted)));
    }

    public void Dispose()
    {
        _rijndael.Dispose();
        _encryptor.Dispose();
    }

    public string Encrypt(string unencrypted)
    {
        return Convert.ToBase64String(Encrypt(_encoder.GetBytes(unencrypted)));
    }

    private byte[] Decrypt(byte[] buffer)
    {
        // IV is prepended to cryptotext
        byte[] iv = buffer.Take(IvBytes).ToArray();
        using (ICryptoTransform decryptor = _rijndael.CreateDecryptor(_rijndael.Key, iv))
        {
            return decryptor.TransformFinalBlock(buffer, IvBytes, buffer.Length - IvBytes);
        }
    }

    private byte[] Encrypt(byte[] buffer)
    {
        // Prepend cryptotext with IV
        byte [] inputBuffer = _encryptor.TransformFinalBlock(buffer, 0, buffer.Length); 
        return _rijndael.IV.Concat(inputBuffer).ToArray();
    }
}

Update 2015-07-18: Fixed mistake in private Encrypt() method by comments of @bpsilver and @Evereq. IV was accidentally encrypted, is now prepended in clear text as expected by Decrypt().