Slashdot Mirror
Researcher Wants To Protect Whistleblowers Against Hidden Printer Dots (bleepingcomputer.com)
An anonymous reader writes: "Gabor Szathmari, a security researcher for CryptoAUSTRALIA, is working on a method of improving the security of leaked documents by removing hidden dots left behind by laser printers, which are usually used to watermark documents and track down leakers," reports Bleeping Computer. "Szathmari's work was inspired by the case of a 25-year-old woman, Reality Leigh Winner, who was recently charged with leaking top-secret NSA documents to a news outlet." According to several researchers, Winner might have been caught after The Intercept had shared some of the leaked documents with the NSA. These documents had the invisible markings left behind by laser printers, which included the printer's serial number and the date and time when the document was printed. This allowed the NSA to track down Winner and arrest her even before she was able to publish the leaked documents. Now, Szatmari has submitted a pull request to the PDF Redact Tools, a project for securely redacting and stripping metadata from documents before publishing. Szathmari's pull request adds a code routine to the PDF Redact Tools project that would allow app operators to convert documents to black and white before publishing. "The black and white conversion will convert colors like the faded yellow dots to white," Szathmari said in an interview. Ironically, the project is managed by First Look Media, the parent company behind The Intercept news outlet.
Long before laser printers, investigators were tying people to typewriters based on unique per-unit imperfections and wear patterns. You can do something similar based on drum and toner distribution variances even on a monochrome non-watermarked printer.
Granted, the judas dots also report the date and time, which helps nail a culprit on a shared resource, but the safest thing to do would be to OCR the printed documents rather than photocopy them.