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Author Topic: Food for thought - Why printers add secret dots  (Read 815 times)

tom b

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Food for thought - Why printers add secret dots
« on: December 30, 2017, 04:48:40 PM »

A very interesting  BBC article. Quotes:

"At that point, experts began taking a closer look at the document, now publicly available on the web. They discovered something else of interest: yellow dots in a roughly rectangular pattern repeated throughout the page. They were barely visible to the naked eye, but formed a coded design. After some quick analysis, they seemed to reveal the exact date and time that the pages in question were printed: 06:20 on 9 May, 2017 – at least, this is likely to be the time on the printer’s internal clock at that moment. The dots also encode a serial number for the printer.

These “microdots” are well known to security researchers and civil liberties campaigners. Many colour printers add them to documents without people ever knowing they’re there."

"Some forms of text-based steganography don’t even use alphanumeric characters or symbols at all. Alan Woodward, a security expert at the University of Surrey, notes the example of ‘Snow’ –  Steganographic Nature Of Whitespace – which places spaces and tabs at the end of lines in a piece of text. The particular number and order of these white spaces can be used to encode an invisible message.

“Locating trailing whitespace in text is like finding a polar bear in a snowstorm,” the Snow website explains.

Now if we could just decipher BC's many spaces after a period we could have an interesting story. ::)

Cheers,

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Tom Brown

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Re: Food for thought - Why printers add secret dots
« Reply #1 on: December 30, 2017, 06:15:11 PM »

This is very old news - it's been known since the 90s.  All colour laser printers and copiers do this (well, there may be some rogue knock-off brands that don't, I suppose, but basically all).  It means that anyone attempting to use them to counterfeit currency can have the fake notes traced back to the printer that made them (and presumably, to whom it was sold etc. as a matter of process).

Inkjets don't do it.
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Phil Brown

Rob C

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Re: Food for thought - Why printers add secret dots
« Reply #2 on: January 01, 2018, 02:40:20 PM »

This is very old news - it's been known since the 90s.  All colour laser printers and copiers do this (well, there may be some rogue knock-off brands that don't, I suppose, but basically all).  It means that anyone attempting to use them to counterfeit currency can have the fake notes traced back to the printer that made them (and presumably, to whom it was sold etc. as a matter of process).

Inkjets don't do it.

I'd have imagined it difficult enough to get the right paper to make counterfeits, but obviously folks do get their entrepreneurial hands on it.

Rob

tom b

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Re: Food for thought - Why printers add secret dots
« Reply #3 on: January 01, 2018, 04:09:31 PM »

From the article:

"Microdots have existed for many years. The Electronic Frontier Foundation (EFF) maintains a list of colour printers known to use them. The images below, captured by the EFF, demonstrate how to decode them:"

The article was more about tracking copies than forgeries. Australian banknotes have a range of security features to the point that if you could forge a note your printing skills would be so high that you could easily make good money legitimately.

As to Rob's comment about paper, Australian money has been printed on clear polymer for quite some time (Pound notes are heading in the same direction).

Cheers,
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Tom Brown

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Re: Food for thought - Why printers add secret dots
« Reply #4 on: January 01, 2018, 04:20:44 PM »

Yeah, it's still very old news - but still interesting :-)

As to paper, Rob, most counterfeits are dumped into the system in small numbers, usually even single notes, and they're not looking for perfection like you see in the movies - just enough for some retailer or bar staff or whoever to accept it, so it didn't need to be particularly good.  Of course, colour laser printers were never the bee's knees in counterfeiting, just cheap and quick and simple and often good enough - enough that governments wanted a way to trace their use!

As Tom says, polymer notes are the way to go:

https://www.rba.gov.au/publications/annual-reports/rba/2000/note-printing.html
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Phil Brown
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