Question

I want to use the cryptography in the Portable Class Library Contrib project on codeplex but have not found any documentation on how I can use it.

I want to create a wrapper class with Encrypt and Decrypt methods inside it and I want this wrapper class to exist in a portable class library. I have referenced Portable.Runtime and Portable.Security.Cryptography in this project. Is this correct?

I then want to use my wrapper inside a .NET, Windows Phone and Metro project. In these projects I reference my wrapper project, Portable.Runtime, Portable.Security.Cryptography and the corresponding Portable project i.e. Portable.Desktop, Portable.Phone or Portable.WindowsStore. Is this correct?

I get conflicting namespace errors when I try to use my wrapper class however. This is the error and my wrapper class:

The type System.Security.Cryptography.AesManaged exists in both C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\Profile\Client\System.Core.dll and C:\Downloads\PclContrib\bin\Debug\Portable.Security.Cryptography.dll

public sealed class SymmetricCryptography<T> where T : SymmetricAlgorithm, new()
{
    private readonly T provider = new T();
    private readonly UTF8Encoding utf8 = new UTF8Encoding();

    private byte[] key;
    private byte[] iv;

    public byte[] Key
    {
        get { return this.key; }
    }

    public byte[] IV
    {
        get { return this.iv; }
    }

    public SymmetricCryptography()
    {
        this.key = this.provider.Key;
        this.iv = this.provider.IV;
    }

    public SymmetricCryptography(byte[] key, byte[] iv)
    {
        this.key = key;
        this.iv = iv;
    }

    public SymmetricCryptography(string password, string salt)
    {
        Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes(password, this.utf8.GetBytes(salt));
        this.key = deriveBytes.GetBytes(this.provider.KeySize >> 3);
        this.iv = deriveBytes.GetBytes(16);
    }

    public SymmetricCryptography(string password, string salt, int iterations)
    {
        Rfc2898DeriveBytes deriveBytes = new Rfc2898DeriveBytes(password, this.utf8.GetBytes(salt), iterations);
        this.key = deriveBytes.GetBytes(this.provider.KeySize >> 3);
        this.iv = deriveBytes.GetBytes(16);
    }

    public byte[] Encrypt(byte[] input)
    {
        return this.Encrypt(input, this.key, this.iv);
    }

    public byte[] Encrypt(byte[] input, byte[] key, byte[] iv)
    {
        return this.Transform(
            input,
            this.provider.CreateEncryptor(key, iv));
    }

    public byte[] Decrypt(byte[] input)
    {
        return this.Decrypt(input, this.key, this.iv);
    }

    public byte[] Decrypt(byte[] input, byte[] key, byte[] iv)
    {
        return this.Transform(
            input,
            this.provider.CreateDecryptor(key, iv));
    }

    public string Encrypt(string text)
    {
        return this.Encrypt(text, this.key, this.iv);
    }

    public string Encrypt(string text, byte[] key, byte[] iv)
    {
        byte[] output = this.Transform(
            this.utf8.GetBytes(text),
            this.provider.CreateEncryptor(key, iv));
        return Convert.ToBase64String(output);
    }

    public string Decrypt(string text)
    {
        return this.Decrypt(text, this.key, this.iv);
    }

    public string Decrypt(string text, byte[] key, byte[] iv)
    {
        byte[] output = this.Transform(
            Convert.FromBase64String(text),
            this.provider.CreateDecryptor(key, iv));
        return this.utf8.GetString(output, 0, output.Length);
    }

    public void Encrypt(Stream input, Stream output)
    {
        this.Encrypt(input, output, this.key, this.iv);
    }

    public void Encrypt(Stream input, Stream output, byte[] key, byte[] iv)
    {
        this.TransformStream(true, ref input, ref output, key, iv);
    }

    public void Decrypt(Stream input, Stream output)
    {
        this.Decrypt(input, output, this.key, this.iv);
    }

    public void Decrypt(Stream input, Stream output, byte[] key, byte[] iv)
    {
        this.TransformStream(false, ref input, ref output, key, iv);
    }

    private byte[] Transform(
        byte[] input,
        ICryptoTransform cryptoTransform)
    {
        byte[] result;

        using (MemoryStream memoryStream = new MemoryStream())
        {
            using (CryptoStream cryptStream = new CryptoStream(
                memoryStream,
                cryptoTransform,
                CryptoStreamMode.Write))
            {
                cryptStream.Write(input, 0, input.Length);
                cryptStream.FlushFinalBlock();
                memoryStream.Position = 0;
                result = memoryStream.ToArray();
            }
        }

        return result;
    }

    private void TransformStream(bool encrypt, ref Stream input, ref Stream output, byte[] key, byte[] iv)
    {
        // defensive argument checking
        if (input == null)
        {
            throw new ArgumentNullException("input");
        }

        if (output == null)
        {
            throw new ArgumentNullException("output");
        }

        if (!input.CanRead)
        {
            throw new ArgumentException("Unable to read from the input Stream.", "input");
        }

        if (!output.CanWrite)
        {
            throw new ArgumentException("Unable to write to the output Stream.", "output");
        }

        // make the buffer just large enough for 
        // the portion of the stream to be processed
        byte[] inputBuffer = new byte[input.Length - input.Position];
        // read the stream into the buffer
        input.Read(inputBuffer, 0, inputBuffer.Length);
        // transform the buffer
        byte[] outputBuffer = encrypt ? Encrypt(inputBuffer, key, iv)
                                        : Decrypt(inputBuffer, key, iv);
        // write the transformed buffer to our output stream 
        output.Write(outputBuffer, 0, outputBuffer.Length);
    }
}

Answer 1

It turns out that my generic wrapper for the cryptography algorithms was causing a problem. PCL Contrib contains a class called SymmetricAlgorithm which is itself a wrapper for the real SymmetricAlgorithm. If I make my wrapper class non-generic it works like this:

public sealed class AesManagedSymmetricCryptography : SymmetricCryptography<AesManaged>
{
    #region Constructors

    public AesManagedSymmetricCryptography()
    {
    }

    public AesManagedSymmetricCryptography(byte[] key, byte[] iv)
        : base(key, iv)
    {
    }

    public AesManagedSymmetricCryptography(string password, string salt)
        : base(password, salt)
    {
    }

    public AesManagedSymmetricCryptography(string password, string salt, int iterations)
        : base(password, salt, iterations)
    {
    }

    #endregion
}