<http://news.bbc.co.uk/2/low/technology/3753886.stm> The BBC | Entertainment | Have Your Say | In Pictures | Week at a Glance Monday, 18 October, 2004, 16:58 GMT 17:58 UK Printers betray document secrets That staple of crime novels - solving a case by identifying the typewriter used to write a ransom note - is being updated for the modern day. US scientists have discovered that every desktop printer has a signature style that it invisibly leaves on all the documents it produces. They have now found a way to use this to identify individual laser printers. The work will help track down printers used to make bogus bank notes, fake passports and other important papers. Spot colour Before now it was thought that the differences between cheap, mass-produced desktop printers were not significant enough to make individual identification possible. But a team from Purdue University in Indiana led by Professor Edward Delp has developed techniques that make it possible to trace which printer was used to produce which document. In 11 out of 12 tests, the team's methods identified which model of desktop laser printer was used to print particular documents. "We also believe that we will be able to identify not only which model of printer was used but specifically which printer was used," Professor Delp said. The image processing software developed by Professor Delp's team looks for the "intrinsic signatures" that each printer produces. Professor Jan Allebach, who helped develop the ID techniques, said the production methods demanded by competition in the desktop printer market meant there was quite a lot of variation in the way different machines printed pages. "For a company to make printers all behave exactly the same way would require tightening the manufacturing tolerances to the point where each printer would be too expensive for consumers," he said. The differences emerge in the way that a laser printer lays down ink on the paper and which can be spotted with the Purdue system. Inkjet is next Typically, different printers lay down ink in distinct bands that can be spotted by image processing software. "We extract mathematical features, or measurements, from printed letters, then we use image analysis and pattern-recognition techniques to identify the printer," said Professor Delp. Desktop printers coupled with scanners have become favourites with forgers as they produce high-quality copies of banknotes and personal documents that can fool a casual glance. The team is now working to extend its techiques to cover inkjet printers. The team is also working on ways to manipulate printers so they lay down ink with more easily identifiable signatures. The researchers will present their detailed findings at the International Conference on Digital Printing Technologies in early November. -- ----------------- R. A. Hettinga <mailto: rah@ibuc.com> The Internet Bearer Underwriting Corporation <http://www.ibuc.com/> 44 Farquhar Street, Boston, MA 02131 USA "... however it may deserve respect for its usefulness and antiquity, [predicting the end of the world] has not been found agreeable to experience." -- Edward Gibbon, 'Decline and Fall of the Roman Empire'
R.A. Hettinga wrote:
US scientists have discovered that every desktop printer has a signature style that it invisibly leaves on all the documents it produces.
I don't think this is new - I'm pretty sure it was published about 6 or 7 years back as a technique. iang
On Tue, 2004-10-19 at 16:14, Ian Grigg wrote:
R.A. Hettinga wrote:
US scientists have discovered that every desktop printer has a signature style that it invisibly leaves on all the documents it produces.
I don't think this is new - I'm pretty sure it was published about 6 or 7 years back as a technique.
I think you're thinking of color copiers.
At 05:23 PM 10/18/2004, R.A. Hettinga wrote:
It turns out that their techniques aren't all that useful. Changing laser printer cartridges changes the results. You might find that two documents were printed by the same printer, but it doesn't give you the options for tracking it down that manual typewriters did. And the differences don't identify a specific printer in a way that can be tracked, e.g. identifying a serial number that could be looked up from warranty records. It's not clear that they work at all with inkjet printers, and changing ink cartridges is even more common than changing laser printer cartridges. If you're sloppy, you've probably got a bunch of partly-used cartridges around, so even if you want to print out a bunch of ransom notes or whatever, you don't even have to go to Kinko's to get them to be different. If printer makers want to build in watermarking to make everything they print traceable, the way many of them check for documents that look like money and don't print them, they could hide patterns that survive cartridge changes (would you notice a few inverted pixels on a 600x600dpi printout?) But even then, inkjet printers are dirt cheap; when they're on sale, they're essentially a free enclosure in a box of overpriced printer cartridges, so even of the printer wants to rat out the user and it's not easy to change the serial number PROM, you can just replace the printer. ---- Bill Stewart bill.stewart@pobox.com
I seem to recall hearing a rumour that suggested that for years now, photocopiers have been leaving their serial number on the copies they produce. If true, and I am inclined to believe it, it follows naturally that something similar might happen with laser-printers and ink-jet printers. Ian Grigg <iang@systemics.com> wrote: R.A. Hettinga wrote:
US scientists have discovered that every desktop printer has a signature style that it invisibly leaves on all the documents it produces.
I don't think this is new - I'm pretty sure it was published about 6 or 7 years back as a technique. iang --------------------------------- Post your free ad now! Yahoo! Canada Personals
Simple way to test. Get two printers of the same make and model. Print identical documents on both printers, scan them, diff the scans. Some will be noise, repeat several times, see which noise repeats and you get closer and closer to the serial #'s. ----------------------Kaos-Keraunos-Kybernetos--------------------------- + ^ + :"Our enemies are innovative and resourceful, and so are we. /|\ \|/ :They never stop thinking about new ways to harm our country /\|/\ <--*-->:and our people, and neither do we." -G. W. Bush, 2004.08.05 \/|\/ /|\ : \|/ + v + : War is Peace, freedom is slavery, Bush is President. ------------------------------------------------------------------------- On Wed, 20 Oct 2004, Steve Thompson wrote:
I seem to recall hearing a rumour that suggested that for years now, photocopiers have been leaving their serial number on the copies they produce. If true, and I am inclined to believe it, it follows naturally that something similar might happen with laser-printers and ink-jet printers.
Ian Grigg <iang@systemics.com> wrote: R.A. Hettinga wrote:
US scientists have discovered that every desktop printer has a signature style that it invisibly leaves on all the documents it produces.
I don't think this is new - I'm pretty sure it was published about 6 or 7 years back as a technique.
iang
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| It turns out that their techniques aren't all that useful. | Changing laser printer cartridges changes the results. | You might find that two documents were printed | by the same printer, but it doesn't give you the | options for tracking it down that manual typewriters did. Actually, they say they can identify the make and model - which is about all you could do with a typewriter. Going further, in either case, means tying a particular piece of text to a particular writing instrument to which you have gained access. Changing printer cartridges will certainly work, but then again simply replac- ing the typewriter will, too. Any identification of physical objects can only work as long as the physical object isn't replaced. In practice, there's a great deal of inertia in replacing physical objects, for cost, convenience, and other reasons. So such identifications may still be useful. | And the differences don't identify a specific printer | in a way that can be tracked, e.g. identifying a serial number | that could be looked up from warranty records. A bullet can't be tied to a gun's serial number, but that doesn't make it useless to examine bullets. | It's not clear that they work at all with inkjet printers, | and changing ink cartridges is even more common than | changing laser printer cartridges. The technique is based on variations in dot pattern that ultimately come down to small variations in mechanical parts, usually the gears that drive the paper. Laser printer cartridges are deliberately designed so that (just about) all moving/wearing parts are part of the cartridge. So most variations in the results are necessarily tied to the cartridge. That's not true for ink jets. While the paper describing all this isn't yet available, from what is published I don't think they are making any claims about inkjets, just laser printers. However, they seem to believe the same general approach - look for variations due to variations in manufacture that don't produce artifacts that are visible to the naked eye, so don't need to be and hence are not controlled - would work. Whether the source of the variation would be in the ink cartridge or in the fixed mechanicals, who can say at this point. | If you're sloppy, | you've probably got a bunch of partly-used cartridges around, | so even if you want to print out a bunch of ransom notes | or whatever, you don't even have to go to Kinko's | to get them to be different. | | If printer makers want to build in watermarking to | make everything they print traceable, the way many of them | check for documents that look like money and don't print them, | they could hide patterns that survive cartridge changes | (would you notice a few inverted pixels on a 600x600dpi printout?) Actually, this would probably be noticable in certain pictures. But slight variations in pixel spacing - which is what these guys look for - is not visible. (In fact, the origin of this work seems to have been work in the opposite direction: Early laser printers had a problem with banding, due to periodic variations in paper movement causing variations in pixel spacing. The trick was to find out how much variation you could allow without visible artifacts and then get to that level cheaply. But there is still plenty of variation left for appropriate software to find.) You could probably play games with pixel sizes, too. | But even then, inkjet printers are dirt cheap; | when they're on sale, they're essentially a free enclosure | in a box of overpriced printer cartridges, | so even of the printer wants to rat out the user and | it's not easy to change the serial number PROM, | you can just replace the printer. One could say the same about most physical objects that end up being used for identification. You would think that fibers would be useless for identification, for example - you can always throw out the clothing you were wearing and buy a new tee shirt. Still ... the real world has a great deal of inertia. -- Jerry
Bear in mind that typewrites have been traced by the minute, unique characteristics of the metal face of character producers, whether lever-type or ball. The FBI has been doing this quite a while. Micro-forensics of the unique printing mechanism of each machine is likely possible. Identification in this manner would have nothing to do with toner cartridges or machine numbers, although it would probably take a sophisticated laboratory to make the match. As with most intelligence involving technology, it is not the obvious that reveals but conceals the less than obvious, at several depths of deception. Software registration numbers don't mean much compared to what is snarfed when you log on to register a product -- not to mention those sneaky handshakes of PKs and TTPs and SSHs and Extra-Secure Certificates. Take a gander at a Wash Post Op-Ed from a few days ago that explained what has been explained years ago on this sacred list about technological and intelligence deception, in particular the role of media yokeling the public: http://cryptome.org/intel-pr.htm To be sure the Op-Ed, written by someone at MIT's Security Studies Center (wah!), may be an example of what it speaks, but not this message from god: there will be no casualities, James, dogdamn it, no pain and suffering, just lip flapping about the horror deserved.
participants (8)
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Bill Stewart -
Ian Grigg -
Jerrold Leichter -
John Young -
R.A. Hettinga -
Steve Furlong -
Steve Thompson -
Sunder