SecureDesktop.cs

using System;
using System.Threading;
using System.Windows;
using System.Windows.Controls;
using System.Runtime.InteropServices;
using System.Windows.Threading;

class Program
{
    // DESKTOP_ACCESS
    const UInt32 DESKTOP_NONE            = 0x0000u;
    const UInt32 DESKTOP_READOBJECTS     = 0x0001u;
    const UInt32 DESKTOP_CREATEWINDOW    = 0x0002u;
    const UInt32 DESKTOP_CREATEMENU      = 0x0004u;
    const UInt32 DESKTOP_HOOKCONTROL     = 0x0008u;
    const UInt32 DESKTOP_JOURNALRECORD   = 0x0010u;
    const UInt32 DESKTOP_JOURNALPLAYBACK = 0x0020u;
    const UInt32 DESKTOP_ENUMERATE       = 0x0040u;
    const UInt32 DESKTOP_WRITEOBJECTS    = 0x0080u;
    const UInt32 DESKTOP_SWITCHDESKTOP   = 0x0100u;

    const UInt32 dwDesiredAccess =
        DESKTOP_READOBJECTS  |
        DESKTOP_CREATEWINDOW |
        DESKTOP_CREATEMENU   |
        DESKTOP_WRITEOBJECTS |
        DESKTOP_SWITCHDESKTOP;

    [DllImport("kernel32.dll")] static extern uint GetCurrentThreadId();
    [DllImport("user32.dll")]   static extern IntPtr GetThreadDesktop(uint dwThreadId);
    [DllImport("user32.dll")]   static extern IntPtr CreateDesktop(string desktopName, IntPtr device, IntPtr deviceMode, uint flags, uint accessMask, IntPtr attributes);
    [DllImport("user32.dll")]   static extern bool SetThreadDesktop(IntPtr hDesktop);
    [DllImport("user32.dll")]   static extern bool CloseDesktop(IntPtr hDesktop);
    [DllImport("user32.dll")]   static extern bool SwitchDesktop(IntPtr hDesktop);

    [STAThread]
    public static void Main()
    {
        var btn = new Button() { Content = "Open secure desktop" };
        btn.Click += (s, e) => SecureDialog();
        var win = new Window() { Content = btn };
        new Application().Run(win);
    }

    static void SecureDialog()
    {
        var hOldDesktop = GetThreadDesktop(GetCurrentThreadId());
        var hNewDesktop = CreateDesktop("My desktop", IntPtr.Zero, IntPtr.Zero, 0, dwDesiredAccess, IntPtr.Zero);
        SwitchDesktop(hNewDesktop);

        var thread = new Thread( () => SecureDesktopThread(hNewDesktop) );
        thread.SetApartmentState(ApartmentState.STA);
        thread.Start();
        thread.Join();  // Wait for thread to complete.

        SwitchDesktop(hOldDesktop);
        CloseDesktop(hNewDesktop);
    }

    static void SecureDesktopThread(IntPtr hNewDesktop)
    {
        SetThreadDesktop(hNewDesktop);

        SynchronizationContext.SetSynchronizationContext(
            new DispatcherSynchronizationContext(Dispatcher.CurrentDispatcher));

        var win = new Window() { Content = "Hello World!", FontSize=30 };
        win.ShowDialog();
        Dispatcher.CurrentDispatcher.InvokeShutdown();
    }
}