Via Freedom to Tinker:
From banknotes to contracts, authenticating printed documents has been a longstanding challenge. Here’s what the surface of paper looks like under a microscope:
Now Princeton University security expert Ed Felten and other researchers claim they have devised a way to generate a 3D “fingerprint” of any piece paper via an ordinary scanner, in a study (PDF) to be published in May:
This paper presents a novel technique for authenticating physical documents based on random, naturally occurring imperfections in paper texture. We introduce a new method for measuring the three-dimensional surface of a page using only a commodity scanner and without modifying the document in any way. From this physical feature, we generate a concise fingerprint that uniquely identifies the document. Our technique is secure against counterfeiting and robust to harsh handling; it can be used even before any content is printed on a page. It has a wide range of applications, including detecting forged currency and tickets, authenticating passports, and halting counterfeit goods. Document identification could also be applied maliciously to de-anonymize printed surveys and to compromise the secrecy of paper ballots.
So what’s the significance of this approach?
Our work shows that ordinary pieces of paper can be ﬁngerprinted and later identiﬁed using commodity desktop scanners. The technique we developed functions like a “biometric” for paper and allows original documents to be securely and reliably distinguished from copies or forgeries.
And how successful can it be?
The security of our methods against forgery, in cases where the adversary has full access to information, will depend ultimately on a race between the resolution of the printers that can create patterns on a page, and the resolution of the scanners that can observe patterns.
The ideal solution, of course, would be an iPhone with a powerful enough lens and light source coupled with an app to do the verification anywhere.