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Printer Tracking Dots Back in the News

DEEPLINKS BLOG
June 6, 2017

Several journalists and experts have recently focused on the fact that a scanned document published by The Intercept contained tiny yellow dots produced by a Xerox DocuColor printer. Those dots allow the document's origin and date of printing to be ascertained, which could have played a role in the arrest of Reality Leigh Winner, accused of leaking the document. EFF has previously researched this tracking technology at some length; our work on it has helped bring it to public attention, including in a somewhat hilarious video.

One of the experts, Rob Graham, used a tool that we created to decode the dots. Whenever someone's liberty is at stake, we are extra careful in our public statements, but we offer the following thoughts on the situation:

  •  The affidavit that led to Winner's arrest described how the government identified its suspect. The affidavit did not mention the use of the tracking dots at all, but referred only to other sources of information. It's quite possible that printer dots did not play any role in this investigation at all.
  • However the government identified its suspect in this case, it's worth remembering that forensic techniques are very powerful and can often reveal the origins of documents in unexpected ways.
  • This tracking technology is pervasive in color laser printers, and is a result of secret agreements between governments (the U.S. is not the only one) and the printer industry, dating back more than a decade. Some printer manufacturers openly acknowledge that such a tracking mechanism exists, but offer few other details. The original motivation given for the tracking technology is investigating counterfeiting of currency, although nothing in the technology limits its use to that purpose. Overall, this secret nonconsensual tracking makes it more difficult to publish any kind of document anonymously, which implicates both privacy and speech.
  • Not all printers' tracking information is readily visible. Some of the documents we obtained about this technology showed that there is a subsequent generation of tracking technology, which apparently works by slightly rearranging dots that the printer is expected to print, rather than by adding new dots. Anyone using a color laser printer should assume that it uses some kind of tracking mechanism, whether or not tracking dots are visible in its output.
  • This technology is one way that governments secretly pressured industry to change products to undermine privacy and anonymous speech when the law did not require it. This should make us all wonder how else the government is working in secret to undermine privacy and speech.  We should insist that companies be transparent about how government requests have affected the design of the products we use, since those designs can have profound implications.
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