P/Invoking CryptImportKey and marshaling structs

// 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;
    }

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);