[Printers] software release: yellowdot

[Seth David Schoen]

I Miller writes:

> Thanks for the rapid reply, Seth!  I'm extremely interested in the brochure
> produced by EFF - is there an online copy available?

Not yet, but hopefully soon.

> A question: are there known printer watermarking schemes that involve
> permutations of the watermark across the printed sheet?  In the case of
> Xerox DocuColor, it appears that there isn't any "room" in the watermark for
> such information, and it suggests to me that the same watermark is repeated
> across the sheet.  Therefore, in the case of DocuColor printers, the
> logical-AND method propose proposed by Seth Schoen would be a trivial attack
> against the random-dot overlay generated by yellowdot.

Everything I've looked at closely enough has a simple repeated (tiled)
translation of an identical pattern at some particular period, at least
within a given page.

> However, a more sophisticated watermarking technique (checksumming the row
> and column, or perhaps encryption) would require more sophisticated analysis
> to disambiguate yellowdot noise.

That's definitely true, if there turn out to be printers that do this.
My impression is that there might be a tradeoff from the point of view
of the tracking code embedder between resisting truly random noise or
errors (which is best done by a completely periodic signal) and resisting
deliberately added decoy noise (which is best done by a signal that varies
in a way that the decoder can predict but that the printer user can't
predict easily).

> I think Seth Schoen's challenge sounds like lots of fun.  I don't have a
> laser printer, but I'm happy to find a local print shop for this purpose.
> However, if anyone else has faster access to a DocuColor printer, by all
> means take advantage of that access!

The DocuColors are pretty easily available at Fedex Kinko's locations,
though I don't know whether they'll be willing to tell you the serial
number.  (However, you can figure it out for yourself using the
decoder or decoding information on our web site ... if you print one
test page without the obfuscating dots in order to learn the serial
number, and another test page with the obfuscating dots to send to me.)
Many locations let you send print jobs over the Internet, though I
don't remember whether you need to speak to a person to be absolutely
sure you'll get your job run on a DocuColor.

> Finally, as a general question to the list: I have followed the printer
> watermark _decoding_ meme for several years now, but have there been other
> proactive attempts, aside from yellowdot, to _obfuscate_ printer
> watermarking?

I don't think so, but I've been doing some preliminary experiments in
that direction.  I'd be happy to know if anybody else has made progress
on this.

-- 
Seth Schoen
Staff Technologist                                schoen at eff.org
Electronic Frontier Foundation                    http://www.eff.org/
454 Shotwell Street, San Francisco, CA  94110     1 415 436 9333 x107