Password protecting a drawing using the AutoCAD.Net API

By Balaji Ramamoorthy

The links provided in the code refer to MSDN documentation. These can help you choose a provider and the key length. Since “RC4” is the only algorithm supported by AutoCAD, it important to select the key length from the list keeping this in mind.

[CommandMethod("PwdProtect")]
static public void PwdProtectMethod()
{
    String dwgFilePath = "C:\Test.dwg";
    if (!System.IO.File.Exists(dwgFilePath))
        return;
 
    string password = "Autodesk";
 
    // Choose a provider name from the list of providers
    //http://msdn.microsoft.com/en-us/library/windows/desktop/
    //aa380243(v=vs.85).aspx
    string providerName
        = "Microsoft Enhanced Cryptographic Provider v1.0";
 
    string subject = null;
    string issuer = null;
    string serialNumber = null;
    string comment = null;
    string timeServer = null;
    SecurityActions actions = SecurityActions.EncryptData;
    SecurityAlgorithm algorithm = SecurityAlgorithm.RC4;
 
    // Find the default/min/max key length 
    // for the provider name used
    // http://msdn.microsoft.com/en-us/library/windows/desktop/
    // bb931357(v=vs.85).aspx
 
    uint keyLength = 128;
    uint providerType = 1;
 
    try
    {
        using (Database db = new Database(false, true))
        {
            db.ReadDwgFile
                (
                    dwgFilePath,
                    System.IO.FileShare.ReadWrite,
                    true,
                    ""
                );
 
            SecurityParameters sp
                = new SecurityParameters
                                        (
                                            password,
                                            providerName,
                                            subject,
                                            issuer,
                                            serialNumber,
                                            comment,
                                            timeServer,
                                            actions,
                                            algorithm,
                                            keyLength,
                                            providerType
                                        );
            db.SaveAs
                    (
                        db.Filename,
                        false,
                        DwgVersion.Current,
                        sp
                    );
        }
    }
    catch (System.Exception ex)
    {
        Editor ed =
        Application.DocumentManager.MdiActiveDocument.Editor;
 
        ed.WriteMessage(ex.Message);
    }
}

-Balaji