P/Invoking CryptImportKey and marshaling structs

Question

I'm trying to P/Invoke into CryptImportKey from C# to set a known key before encrypting data that will be decrypted in a C++ Win32 service at some point. I have the method signature for the P/Invoke and that all works fine but i can't get it to accept my key blob. The C++ structs are in comments below and my C# ones for marshaling are underneath.

        // typedef struct _PUBLICKEYSTRUC 
    // {
    //    BYTE bType;  
    //    BYTE bVersion;  
    //    WORD reserved;  
    //    ALG_ID aiKeyAlg;
    // } BLOBHEADER, PUBLICKEYSTRUC;
    [StructLayout(LayoutKind.Sequential)]
    public struct PUBLICKEYSTRUC
    {
        public Byte bType;
        public Byte bVersion;
        public Int16 reserved;
        public Int32 aiKeyAlg;
    }

    //typedef struct __KEYBLOB 
    //{
    //    BLOBHEADER hdr;
    //    DWORD cbKeySize;
    //    BYTE* rgbKeyData;
    //} KEYBLOB;

    [StructLayout(LayoutKind.Sequential)]
    public struct KEYBLOB
    {
        public PUBLICKEYSTRUC hdr;
        public Int16 cbKeySize;
        public Byte[] rgbKeyData;
    }

I then use:

        int len = (Marshal.SizeOf(typeof(PUBLICKEYSTRUC) + Marshal.SizeOf(typeof(KEYBLOB)) + KeySize;
        byte[] arr = new byte[len];
        IntPtr ptr = Marshal.AllocHGlobal(len);
    Marshal.StructureToPtr(keyBlob, ptr, true);
    Marshal.Copy(ptr, arr, 0,len);
        Marshal.FreeHGlobal(ptr);

To get in to a byte array to pass to CryptImportKey but it never seems to take the key with it and when I encrypt with it I get different cipher text time suggesting it's not using my key.

Any ideas would be great!

EDIT:

The key blob stuff is from the C++ code I have that can successfully encrypt and decrypt the data. I think you maybe have a point about the header being included twice but the main problem I have is the value of the Byte[] rgbKeyData is not being put in to the byte array arr.

Answer 1

Here is a list of structs / imports, which look quite promising. Haven't tested it by myself, though.

Edit:
When you compute the size of your blob: could it be you're actually counting the header twice? Besides, how did you derive the declaration of your KEYBLOB structure?

Answer 2

On the other hand, why are you even bothering with all this P/Invoke stuff here? The .NET Framework has built-in classes to do all this for you.

Assuming you're using RSA encryption, the RSACryptoServiceProvider class provides an ImportParameters method that accepts a RSAParameters object.
Clean, simple, and the right way to do it.

Is there any reason you can't use this?