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List of Printers Which Do or Do Not Display Tracking Dots

(www.eff.org)
586 points prawn | 4 comments | 06 Jun 17 22:12 UTC | HN request time: 2.093s | source
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schoen ◴[06 Jun 17 23:30 UTC] No.14502425[source]▶
I wrote this article/originally created this list, and I would like to emphasize that there is a second generation of this technology that probably uses dithering parameters or something of that sort, and that does not produce visible dots but still creates a tracking code. We don't know the details but we do know that some companies told governments that they were going to do this, and that some newer printers from companies that the government agencies said were onboard with forensic marking no longer print yellow dots.

That makes me think that it may have been a mistake to create this list in the first place, because the main practical use of the list would be to help people buy color laser printers that don't do forensic tracking, yet it's not clear that any such printers are actually commercially available.

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captainmuon ◴[07 Jun 17 07:35 UTC] No.14504357[source]▶
Is somebody working on identifying these modern watermarks? A start would be to print out test pages and compare high resolution scans. Maybe also multiple printouts from the same printer to see what the natural variation is, and if there is a timestamp component.

I would start, but I'm currently not around a printer...

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1. pbhjpbhj ◴[07 Jun 17 09:30 UTC] No.14504803[source]▶
Surely we can skip the paper stage and hookup the motors used for head positioning control to a rig - either reading through rotary measure or preferably reading the signal to the motors directly.

Print the same page, compare the signals sent to the motors? Won't that be a more easily/accurately measure proxy for what's actually being printed. One might need the timing data for the jets on an inkjet too, etc.

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2. dom0 ◴[07 Jun 17 09:46 UTC] No.14504857[source]▶
No printer controls their motors with >600 dpi resolution. Inkjet printers have print heads with many nozzles; the motors do the rough positioning / slide the head over the paper, the nozzles do the hard work. In laser printers a motor only moves the paper along (all rollers are either free-running or synchronized by gears).

So for an inkjet you'd have to look at the nozzle timing, which might be difficult depending on how integrated the drivers are (e.g. if they're a custom chip on a flexprint behind the heads... uhm...). For a laser printer you'd have to look at the laser modulation signal. That should be much easier, bugs have done that before.

Reverse engineering the firmware might be easier... on the other hand, the firmware is probably bolted shut rather well — the printer manufacturers cartridge DRM is in there somewhere.

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3. dithering ◴[07 Jun 17 10:30 UTC] No.14505037[source]▶
Maybe "just after the electronics, but before the print heads/motors" is the appropriate place to probe. It might be more work than anyone's prepared to put in (and of questionable utility), but you could emulate the motors and heads, and generate an image of what would have been printed.
4. pbhjpbhj ◴[07 Jun 17 12:39 UTC] No.14505813[source]▶
I was assuming the nozzles has some sort of actuator that approximates to the term "motor" - I think you're either driving a tiny heater, or piezo, or a charge deflector plate in inkjet printing? That presumably is where the jitter would physically manifest; so you'd look at the input signal to those elements?

Reversing the firmware though, good call.