http://www.bbc.com/future/story/20150624-the-secret-codes-of-british-banknotes
http://www.cl.cam.ac.uk/~mgk25/eurion.pdf
http://www.cl.cam.ac.uk/~sjm217/projects/currency/
!!WARNING!! Photographing bank-notes is illegal in the UK & many other countries.
This is a story of photocopiers, banknotes & secret codes (and as a personal note, you should know that I’m interested in modems, and at the heart of modems are codes, and that leads straight to the Post Office, Queen Elizabeth I & spies & codes & secrets; oh yes).
Xerox is the American company that patented Xerography, a rather clever process for photographing documents (or anything) onto a sensitive metal plate, and then reproducing that photograph as many times as you like on to paper. Although Xerox diversified into many other things (including computers; it was Xerox’s astonishing advances in GUI (“Graphics User Interface”) at the California-based ‘Xerox PARC’ which Bill Gates of Microsoft & Steve Jobs of Apple stole wholesale in 1979/80) their management was brain-dead in everything except photocopiers.
The original photocopiers were B&W (just like the first movies) but, eventually, they found a way to produce good colour copies at a reasonable price. That was--immediately--a direct threat to every government. It’s one thing for criminals to set up shop in a printing works, produce blocks to print bank-notes (needs a *very* skilled operative), source the correct ink & paper then print the notes. There’s not a lot of folks that can do that. However, if it’s just a question of photocopying a banknote, then the police will face investigating damn near every bedroom in every house in the country that contains a teenager. Nightmare!
The story at the bbc.com link above began with Markus Kuhn (2002, then a PhD student at the Computer Laboratory, University of Cambridge) when a wonderful new Xerox colour photocopier was delivered to an office near him. Naturally, being a student, he decided to try it out by copying a £20 GBP note. The machine whirred around for a bit then said “no” (it printed a bit of paper in multiple languages that pointed him to www.rulesforuse.org) (recent image manipulation software such as Adobe Photoshop or Paint Shop Pro will do the same). The interesting question that Markus asked himself was “How did this machine know that it was a banknote?”.
Markus had in his pocket a (then recently released) €10 Euro note, and compared it with the £20 GBP note. It was a bit more obvious on the Euro note, but there was a repeated pattern which subsequently became known as the EURion Constellation; see if you can spot them below (from the PDF above):
The clincher came when he copied the pattern to a blank piece of paper & tried to photocopy that. There were zero problems in B&W but if coloured in then the photocopier produced the same warning; it seems to need to be within the colour channel to activate detection.
Markus named it the “EURion Constellation” partly after the Euro note & partly after the Orion star constellation, which it resembled a bit. Since that time it seems to have been tracked down to the Omron Corporation (a Japanese company) via the Reserve Bank of India (2005). It seems to have been used on banknotes since 1996 & was given an award by the banknote collectors society in 2007.
Now here comes a twist, which every good secret needs:- Steven J. Murdoch (at the same University department as Markus Kuhn) has shown in 2004 that, whilst the EURion Constellation is unequivocally responsible for preventing photocopiers copying banknotes (and will, incidentally, stop you from printing then copying this email) there is a completely different mechanism used within photo-manipulation software. Yup, there are at least 2 different codes in the banknotes to stop them being copied:- one to stop them being photocopied, and the other to stop them being scanned & manipulated.
The top image above is one pixel shorter on the right than the one below. In spite of being full of EURion Constellations it is NOT detected by scanner/image manipulation software as currency (but IS detected by colour photocopiers). The bottom image has all such constellations blanked out yet IS detected by scanners, etc but NOT by the photocopiers. Something else is going on.
This is all a bit Euro-centric so far, so lets let the Yanks into it. Here is a bit of the recent-ish $20 dollar note:
The image at bottom (sourced from an Adobe Forum discussion) actually contains a bit of the $20 note; it does NOT contain any EURion Constellations, yet both Paintshop Pro & Adobe Photoshop say that it is currency & refuse to open it. Stupid computers, huh?
There isn’t a “smoking gun” with this second coding, as there is with the EURion Constellation. Rather, it is a question of digital watermarking. Actually, the ‘smoking gun’ *does* exist, at least in part:- a static disassembly of both programs reveals ‘DMRC’ in the program symbols. DMRC is the stock-sticker code for Digimarc, a company specialising in watermarking. Various news articles have confirmed that Digimarc *did* develop the currency-detection code, on behalf of the Central Bank Counterfeit Deterrence Group (CBCDG), part of the G11 organisation. Also subsequent to Steven’s initial release, Adobe have confirmed their involvement with Digimarc, and stressed how they worked to stop it being worse than it is.
--------- Alex Kemp