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EFF decodes secret color laser printer spy markings

Posted October 18, 2005 @ 10:58 AM
by Jeremy Reimer

The Electronic Frontier Foundation (EFF), the nonprofit organization formed in 1990 by Lotus founder Mitch Kapor to champion users' privacy and information rights in the digital world, has cracked an undocumented set of codes used by all Xerox DocuColor laser printers.

The code is printed on every color page as a series of minuscule yellow dots, arranged on a widely-spaced rectangular 15 by 8 grid. On a regular piece of white printer paper, the faint yellow dots are almost impossible to see, even under magnification. However, when the page is illuminated by a blue LED flashlight, the dots are more clearly visible.

The top and left rows are used as parity bits, for error correction. The remaining dots in the grid are used to convey information about the document and its source, including printer model, printer configuration, printer serial number, and the date and time the page was printed.

The EFF decrypted the binary code by analyzing hundreds of sample pages sent in by volunteers willing to help the project, part of a larger effort to decode any tracking information printed on color lasers. Xerox is by no means the only printer company to have implemented this scheme. Brother, Canon, Dell, Epson, Minolta, Kyocera, Lanier, Lexmark, Savin and Toshiba have all been confirmed to have included such a feature on at least some of their models.

A statement by the EFF underscores the need for concerns about user privacy:

The ACLU recently issued a report revealing that the FBI has amassed more than 1,100 pages of documents on the organization since 2001, as well as documents concerning other non-violent groups, including Greenpeace and United for Peace and Justice. In the current political climate, it's not hard to imagine the government using the ability to determine who may have printed what document for purposes other than identifying counterfeiters.

Yet there are no laws to stop the Secret Service from using printer codes to secretly trace the origin of non-currency documents; only the privacy policy of your printer manufacturer currently protects you (if indeed such a policy exists). And no law regulates what sort of documents the Secret Service or any other domestic or foreign government agency is permitted to request for identification, not to mention how such a forensics tool could be developed and implemented in printers in the first place.

The organization has filed a Freedom of Information (FOIA) request (PDF) with the US government and are still awaiting a response. In the mean time, they encourage anyone with a color laser printer to send them samples to help with the decoding effort. All information gathered by the EFF is treated as strictly confidential, and for those with sensitive privacy concerns there is a manual dot-decoder, as well as GPL'ed source code for creating your own dot-decoder, available on the EFF web site.

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