Scrubbing Metadata from Files- A low-fi approach¶
Files such as Word documents and JPEG images usually contain information about the systems used to create them. This information, commonly referred to as metadata, could inadvertently reveal personally identifiable details about your sources to anyone given access to the files. Removing metadata from files provided by sources before sharing or publishing them is critical for anonymous source protection.
This lesson plan covers what you’ll need to know to find file metadata in Word documents and JPEG files, and how you can share or publish content from these files without exposing metadata.
About This Lesson Plan¶
Review date: June 5 2017
Lesson duration: 45 minutes
What will participants learn?
Basic understanding of what metadata is and basic techniques to “clean” common file formats before publishing or sharing. This session does *not* cover myriad other types of metadata, most notably the metadata created by journalists and sources when they browse the web, use their mobile phones, or communicate using VoIP, chat, email, etc.
What materials will participants need?
Email access, a laptop with MS Word installed, access to printer and scanner
What materials will the instructor need?
Sample document (like a PDF or Word document) and sample image (JPEG or similar format), both with identifying metadata included—such as the name of the Microsoft license-holder, geotag/location data, etc.
How should the instructor prepare?
Review lesson plan, and share example documents from ScrubbingMetadata folder with participants.
Did you know that sharing and publishing files can burn your sources?
Example: Vice and John McAfee: https://www.vice.com/en_us/article/john-mcafee-bath-salts-belize-murder-fugitive-gregory-faull - When Vice published the story, the photos still had location data included and basically burned their source.
Example: How The Intercept Outed Reality Winner - Reality Winner used traditional mail, not the Internet, to share documents with the Intercept, but was caught due to both operational security mistakes and metadata included in the printed files she shared.
Example: BBC: Why printers add secret tracking dots - One mistake that Reality Winner made was to use a color printer to print the documents she leaked. Most color printers add a pattern of yellow dots to any printout, encoding a unique serial number and the date and time that the printout was made. This is ostensibly an anti-counterfeiting measure, originally used by the US Secret Service to identify the source of fake banknotes, but it’s also pretty handy for tracking down whistleblowers who don’t take proper precautions.
[Discussion point: Instructor should ask participants how and when they share documents that they obtained from a source, and what the potential risks are in doing so. Then, if they didn’t come up, the instructor should cover the 3 points below. ]
Sharing outside the newsroom
When you share or publish information obtained from a source, a good rule of thumb is to only share the minimum amount of information necessary to tell a story. In the most extreme case, for example, simply cutting and pasting document text into a plaintext file effectively removes all digital metadata. There may be cases where this isn’t feasible, for example, when you’re sharing a document with a third party to verify its authenticity. Even then, simply sharing the original document may expose your source, so it’s important to remove any file metadata that you can.
Sharing within the newsroom
Even for documents not shared outside the newsroom, removing metadata before sharing with colleagues reduces the risk of an accidental or malicious leak of source information.
Publishing documents with a story
Redaction of information within documents may be necessary before distribution, and it’s important that this be done irreversibly. Some document formats include revision histories, others may still contain text that has been graphically obscured. Metadata scrubbing techniques work well here too. More sophisticated methods of watermarking documents, such as graphical watermarks or typographical variations, may also require a reconstruction of the document be made for publication, as the risk of publishing even the redacted original would be too great.
Metadata-removal software exists, but a simpler approach is to print out a sensitive document, scan it back into your computer and rename the file. Similarly, you can remove metadata from an image or photograph by screenshotting the original and sharing the copy only. (Note that color printers may add nearly-invisible metadata to printed pages as an anti-counterfeiting measure. Printing documents in black and white reduces the chance of exposure.)
(Bonus! Being aware of what kind of metadata exists—and how to find it—also gives you a leg up as a reporter when researching and developing evidence and leads for stories.)
Active Lesson: Removing metadata from a Word doc and a JPEG image¶
[Trainer should begin by introducing participants to the concept of document metadata by showing examples of Word documents and JPEG images, showing where to find the metadata and what types of information may be “hidden” in a document’s guts.]
Finding Microsoft Word metadata
The easiest way to view a Word document’s metadata is to open it in Word and open the Properties dialog:
- In MS Word for OS X, choose File > Properties and select the summary tab.
- In MS Word 2010 and later for Windows, select the File tab, click Info, and select Properties > Advanced Properties on the right-hand side of the pane.
[The instructor should take a moment to review the information included under each tab in the Properties dialog box with participants]
IMAGE:Microsoft Word dialog box showing document metatada
Finding image metadata (EXIF data) Most digital cameras, including smartphone cameras, add metadata to photographs, typically including information about camera settings and the time and location of the shot. You can find this metadata by opening the image information in an image viewing application. For example, in OS X, you can use the built-in Preview App, by opening the image and choosing Tools > Show Location Info.
IMAGE:OS X Preview dialog box showing GPS Location
Scenario: scrubbing metadata
How do you share SOOPERSEKRIT.docx with a third party without exposing the information in the document properties? How do you share MADSCIENTISTLAIR.jpg without giving away the GPS coordinates embedded in the image EXIF data?
[5-10 minute small group discussion: Instructor should ask participants to brainstorm ways they could share or publish the sensitive information. Have each small group report back and see if anyone came up with the idea to retype a document, print and scan, or utilize screenshots. (Spend some time talking about other solutions that came up.)]
Now, split up into pairs, one person pretending to be the journalist with sensitive documents, the other pretending to be a third-party expert in the subject area who is going to review them.
- The “journalist” should print out the document and use a scanner or mobile application to ingest the document (If the “journalist” uses a color printer, the instructor should verify that they printed the document in monochrome.)
- The “journalist” should share the scanned image with the “expert”—for this exercise it doesn’t matter how, but in a real-world scenario the image should be shared securely.
Now, change roles: One person should be a sensitive source with a photo to leak, and the other should be a journalist who is going to receive a “scrubbed” image.
- The “source” should make a screenshot of the original file and send the scrubbed version to the “journalist.”
- The instructor should verify with the “journalist” that the new file’s EXIF data does not contain location info.
- Protecting Your Sources When Releasing Sensitive Documents - a checklist for handling and releasing leaked documents.
- https://exifdata.com/ - an online tool for examining EXIF data in images. (But note that uploading sensitive images to a third-party site is not recommended.)
- Simple questions: What is a file’s metadata and how to edit it in Windows? - a guide to removing file metadata under Windows.
- The Metadata Anonymisation Toolkit - a CLI-based metadata removal toolkit. Some familiarity with UNIX shell commands is a requirement, and the project is not under active maintenance.