PassData Demo

Pass data in a signed PE using the unauthenticated attributes field of the PKCS#7 signature

Projects

• Demo Application
  Source EXE downloaded to the client. Signed using an msbuild task that runs AfterBuild. To demo, enter your code-signing thumbprint into Demo Application.csproj. Uses ILMerge to allow single-file execution.
• Demo Website
  Example website that stamps the download time into the exe as an example
• Demo.Common
  Contains the sentinels used to pass data from the server to the exe
• PassData.ClientSide
  Code used to extract the data from the exe when running on the client
• PassData.ServerSide
  Code used to stamp the data into the exe

Interesting bits

Client side retrieval of data (Demo Application\MainForm.cs)

try
{
    var thisPath = Assembly.GetExecutingAssembly().Location;
    var stampData = StampReader.ReadStampFromFile(thisPath, StampConstants.StampSubject, StampConstants.StampOid);
    var stampText = Encoding.UTF8.GetString(stampData);

    lbStamped.Text = stampText;
}
catch (StampNotFoundException ex)
{
    MessageBox.Show(this, $"Could not locate stamp\r\n\r\n{ex.Message}", Text);
}

Server side stamping (Demo Website\Controllers\HomeController.cs)

var stampText = $"Server time is currently {DateTime.Now} at time of stamping";
var stampData = Encoding.UTF8.GetBytes(stampText);
var sourceFile = Server.MapPath("~/Content/Demo Application.exe");
var signToolPath = Server.MapPath("~/App_Data/signtool.exe");
var tempFile = Path.GetTempFileName();
bool deleteStreamOpened = false;
try
{
    IOFile.Copy(sourceFile, tempFile, true);
    StampWriter.StampFile(tempFile, signToolPath, StampConstants.StampSubject, StampConstants.StampOid, stampData);

    var deleteOnClose = new FileStream(tempFile, FileMode.Open, FileAccess.Read, FileShare.Read | FileShare.Delete, 4096, FileOptions.DeleteOnClose);
    deleteStreamOpened = true;
    return File(deleteOnClose, "application/octet-stream", "Demo Application.exe");
}
finally
{
    if (!deleteStreamOpened)
    {
        try
        {
            IOFile.Delete(tempFile);
        }
        catch
        {
            // no-op, opportunistic cleanup
            Debug.WriteLine("Failed to cleanup file");
        }
    }
}