Fingerprint snap back

You know what I thought when Apple announced the iPhone 5s and confirmed it having a fingerprinter sensor? “Jesus Christ, the amount of virtual ink that’ll be spilled in deploring the sensor and how easy it will be to fake ones fingerprint.”

Alas, of course, we didn’t even have to wait for the phone to actually in people hands. Or fingers.

Here’s Cory Doctorow:

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).


“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.

First of all, “medium to low security” compared to what? A pin?

Next, since the sensor won’t work with a dead, a.k.a. chopped off finger, I’d imagine it’s really difficult to, but not impossible, to simply lift a copy of a fingerprint and use it to open the phone.

Rich Mogull has a pretty comprehensive analysis of the technology and using fingerprints for authentication.

The Touch ID sensor in the iPhone 5s is a capacitive reader, embedded in the home button. That was a good choice on Apple’s part, since capacitive scanners are more accurate and less prone to smudgy fingers, and can’t be faked out with a photocopy of a fingerprint.


But the real reason is that using fingerprints creates better security through improved usability. Most people, if they use a passcode at all, stick with a simple four-digit passcode, which is easy for an attacker to circumvent with physical possession of your iPhone. Longer passphrases, like the obscure 16-character one I use, are far more secure, but a real pain to enter repeatedly. A fingerprint reader, if properly implemented, provides the security of a long passphrase, with more convenience than even a short passcode.

While I welcome Doctorow’s, and others’, pessimism in introducing new security measures and being critical of technologies such as fingerprint readers, I’d also welcome them to not just criticise, but also offer better alternatives.

I don’t think we’ll see many cases of people fingers being chopped off. If for no other reason, then for that charges on ‘nicking a phone’ are quite a bit less serious than on ‘bodily mutilation’.

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