Windows.Security.Cryptography.Core.CryptographicEngine.Encrypt() throwing InvalidCastException

ssedlmayr

Hi, I'm porting some crypto code to UWP for HoloLens. AFAIK, I've implemented it perfectly according to UWP requirements, but I get a mysterious InvalidCastException from the following code:

`public override byte[] Encrypt(byte[] clearData, byte[] Key, byte[] IV) {
#if NETFX_CORE

        IBuffer dataBuffer = WindowsRuntimeBuffer.Create(clearData, 0, clearData.Length, clearData.Length);
        IBuffer keyBuffer = WindowsRuntimeBuffer.Create(Key, 0, Key.Length, Key.Length);
        IBuffer ivBuffer = WindowsRuntimeBuffer.Create(IV, 0, IV.Length, IV.Length);

        string strAlgName = KeyDerivationAlgorithmNames.Pbkdf2Sha256;

        // Open the specified algorithm.
        KeyDerivationAlgorithmProvider objAlgProv = KeyDerivationAlgorithmProvider.OpenAlgorithm(strAlgName);

        // Create a key by using the passed buffer.
        CryptographicKey key = objAlgProv.CreateKey(keyBuffer);

         IBuffer encryptedData = CryptographicEngine.Encrypt(key, dataBuffer, ivBuffer); // throws System.InvalidCastException
         return (byte[])encryptedData.ToArray();`

I'm not really sure what the issue is. I've verified that the types of all parameters being passed into CryptographicEngine.Encrypt are the right type. I tried the AsBuffer extension method earlier on my byte arrays; I switched to WindowsRuntimeBuffer.Create thinking that might do the trick, but it makes no difference whatsoever. dataBuffer and ivBuffer are both of type WindowsRuntimeBuffer, which implements IBuffer, and both are a length that is a multiple of 8 (32 and 16, respectively). I tried casting as IBuffer; that didn't work. I even tried generating 3 random IBuffers, all of lenght 32, to see if that would at least work; it doesn't work. Is this a bug, or am I missing something really obvious? Moreover, the InvalidCastException is completely generic and only gives me the StackTrace from my own app, which tells me absolutely nothing.

ssedlmayr

FWIW, here's the whole stack trace:

at Windows.Security.Cryptography.Core.CryptographicEngine.Encrypt(CryptographicKey key, IBuffer data, IBuffer iv)
at dk.UWP.Crypto.UWPSimpleEncryption.Encrypt(Byte[] clearData, Byte[] Key, Byte[] IV)
at dk.UWP.Crypto.UWPSimpleEncryption.Encrypt(String clearText, String Password)
at dk.Crypto.SimpleEncryption.Encrypt(String clearText, String Password)
at bbtb.Scene.BBTBInitialization.d__19.MoveNext()
at UnityEngine.SetupCoroutine.InvokeMoveNext(IEnumerator enumerator, IntPtr returnValueAddress)
at UnityEngine.SetupCoroutine.$Invoke1InvokeMoveNext(Int64 instance, Int64* args)
at UnityEngine.Internal.$MethodUtility.InvokeMethod(Int64 instance, Int64* args, IntPtr method)

ssedlmayr

I've submitted the following bug report on the Connect website:
https://connect.microsoft.com/VisualStudio/feedback/details/3106919

ssedlmayr

It looks as if, for whatever reason, the examples MSDN provides with KeyDerivationAlgorithmProvider and KeyDerivationAlgorithmNames do not work. If you instead use SymmetricAlgorithmNames and SymmetricAlgorithmProvider, it seems works fine. I'm not sure if this is by design; if so, it is completely undocumented. I will post more information if I discover it.

ssedlmayr

This issue from 2012 fully explains and resolves the issue:
http://answers.flyppdevportal.com/MVC/Post/Thread/85b1b57a-3b4b-420a-b01f-154cdaa68cbc?category=winappswithcsharp
Although it is not clearly documented, different algorithm providers are used for key derivation and encryption.