Why fingerprints make lousy authentication tokens

An "expert" quoted in the Independent predicts that thieves will amputate their victims' fingertips in order to bypass the biometric locks on the new Iphones. I'm not particularly worried about this vulnerability (if you're willing to cut off someone's fingertip to unlock his phone, you're probably also willing to torture him into giving up his PIN), though I remember reading stories of carjackers who amputated their victims' fingertips in order to make off with their biometrically protected cars.

More interesting is the prediction that phone thieves will lift their victims' fingerprints and use them to bypass the readers. As German Interior Minister Wolfgang Schauble discovered, you leak your fingerprints all the time, and once your fingerprint has been compromised, you can't change it. (Schauble was pushing for biometric identity cards; playful Chaos Computer Club hackers lifted his fingerprints off a water-glass after a debate and published 10,000 copies of them on acetate as a magazine insert).

This is the paradox of biometric authentication. The biometric characteristics of your retinas, fingerprints, hand geometry, gait, and DNA are actually pretty easy to come by without your knowledge or consent. Unless you never venture into public without a clean-room bunny-suit, mirrorshades, and sharp gravel in your shoes, you're not going to be able to stop dedicate strangers from capturing these measurements. And as with Schauble's fingerprints, you can't revoke your DNA and replace it with new DNA once a ripoff artist has used it to clean out your bank-account or break into your workplace.

That's why cops use them, after all: it's nearly impossible to keep them to yourself, and once they're in the wild, they can be used against you.

Fraudsters have also succeeded in lifting and duplicating prints with technology that “is only going to improve with time”, he added.

“Thieves in some regions have worked out that you can force a victim to unlock a secured device, and in some extreme cases have also mutilated victims in order to steal their fingerprint.”

The hi-tech scanners are said to work best when combined with a pin code or another security feature.

“Fingerprints can be a useful addition to security but their value depends highly on the type of fingerprint reader and how it is being used - for example, the best use of a fingerprint is to provide a convenient way to unlock something in a medium to low security scenario,” Mr Rogers said.

iPhone 5S: Thieves may mutilate owners in bid to gain access to fingerprint-reading handsets, expert warns [Katie Hodge/The Independent]

(Image: fingerprint closeup, a Creative Commons Attribution (2.0) image from gcfairch's photostream)