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The Register reports
Beating the unique identifiers that printers can add to documents for security purposes is possible: you just need to add extra dots beyond those that security tools already add. The trick is knowing where to add them.
[...] researchers from the Technical University of Dresden [...] Timo Richter, Stephan Escher, Dagmar Schönfeld, and Thorsten Strufe reckon they've cracked the challenge of knowing how to anonymise printed documents, and presented their work to the Association of Computer Machinery's 6th ACM Workshop on Information Hiding and Multimedia Security in Innsbruck, Austria [the week of June 22].
In this paper, the TU Dresden researchers explain that they tested 1,286 documents printed on machines from 18 manufacturers, creating an extraction algorithm to identify well-known dot-patterns--and at the same time, discovering four previously undiscovered patterns coding at 48, 64, 69, and 98 bits.
Identifying new patterns is important, from a privacy point of view, since as the authors points out, an activist in a dictatorship could easily be unmasked by their printer (unless they happen to use a Brother, Samsung, or Tektronix printer, none of which seemed to carry tracking codes, the researchers said).
[...] The group has published [a] toolkit that automates the obfuscation workflow, here.
Previous: "Printer Dot Sanitisation" Software Seeks to Cleanse Yellow-Dot Watermarks
(Score: 2) by maxwell demon on Friday June 29 2018, @08:10AM (6 children)
Let's see.
Let's assume you want to print in 600dpi on A4 (the smallest of the usual paper sizes). An A4 paper has an area of 1/16 square meter, which is slightly less than 97 square inch. Let's assume 90% of that area can be printed on, that gives about 87 square inch, or at 600dpi, a bit more than 31 million pixels.
Let's assume just a B/W printout where each pixel can be either black or white, making one bit per pixel. Then you'll need roughly 31 megabits per page.
Let's take the lower end of typical laser printing speeds, 20 pages per minute, that is, 1/3 page per second. Then with your protocol you'll need to send about 10 megabits per second to the printer.
But what if we have a professional printer with 100 pages per minute, and want to print at 1200 dpi? That's already 100 megabytes per second. Hopefully your printer is connected with Gigabit ethernet …
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by maxwell demon on Friday June 29 2018, @08:11AM (3 children)
Err … should have been megabits, of course.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by maxwell demon on Friday June 29 2018, @08:21AM (2 children)
Err2 … and it would actually be 200 megabits per second (double the resolution is four times the pixels). Which actually drives home my point even more.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by opinionated_science on Friday June 29 2018, @12:05PM (1 child)
surely that's internal? That's why we have(had) Postscript. There's a computer in the printer to turn squiggle's into dots, so you are usually sending a lot less information.
I have heard rumours that in the olden days (1980's) , the printer cpu's were much faster than mainframes for calculation - if you write in Postscript that is ;-)
(Score: 2) by maxwell demon on Friday June 29 2018, @03:18PM
Read the post I replied to. In particular, note the following sentence from that post, emphasis by me:
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by LoRdTAW on Friday June 29 2018, @11:56AM (1 child)
Who says we're starting with 600dpi?
(Score: 2) by maxwell demon on Friday June 29 2018, @03:21PM
Well, for low resolution, I'd just reactivate my old nine-needle printer.
The Tao of math: The numbers you can count are not the real numbers.