Is WRM Safe for XML-based PowerPoint Files?

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All the new Microsoft Office file formats that were introduced with Office 2007 are essentially XML-based. These new formats are distinctive with their X suffixes, so that PPT evolved as PPTX (similarly DOC as DOCX, and XLS as XLSX) — these new file formats continue being used in all subsequent versions of Office on both Windows and Mac. However, they are all essentially ZIP files. The ZIP file acts as a wrapper that contain plenty of XML files and other media content.

So how far would any WRM (Windows Rights Management) protection help? Won’t savvy users be able to unzip those files and get to the content, even without using any WRM credentials? We tested this scenario by adding a ZIP extension to a WRM protected PowerPoint PPTX file, and then tried to unzip the file.

However, the unzipped folder showed up as empty! Follow these steps to see how this process works:

1. Make a copy of any WRM Restricted PowerPoint file, and save it to a folder that is easy to locate, such as your Desktop.
2. Ensure that your system is set to show file extensions. Now, right-click the PowerPoint file, and choose Rename (or just press F2). Add a “.ZIP” without the quotes right after the name of the file – for example if your original file name was:

   Restricted PowerPoint.PPTX

   It would now be renamed to:

   Restricted PowerPoint.ZIP

3. Windows will warn you that renaming the file extension could render this file unusable — but since you are just working on a test file for now, go ahead and ignore this error by clicking the Yes button that you can see in Figure 1.

   
   Figure 1: Change the file extension?

4. Now that you have changed the PPTX to a ZIP file, go ahead and try to unzip the ZIP. We just right-clicked the ZIP file, and chose the Extract option in the resultant contextual menu.
5. Surprise! This brings up a message window that indicates that the compressed (zipped) folder is empty, as shown in Figure 2.

   
   Figure 2: An empty Zip file!

6. Even double clicking the ZIP will bring up an error message, as shown in Figure 3.

   
   Figure 3: Just a ZIP, no unZIP!

This indicates that your WRM (Windows Rights Management) protected presentation is actually fully protected!