If the New iPhone Has Fingerprint Authentication, Can It Be Hacked?

By Bruce Schneier
Wired
September 9, 2013

When Apple bought AuthenTec¬†for its biometrics technology—reported as one of its most expensive purchases—there was a lot of speculation about how the company would incorporate biometrics in its product line. Many speculate that the new Apple iPhone to be announced tomorrow will come with a fingerprint authentication system, and there are several ways it could work, such as swiping your finger over a slit-sized reader to have the phone recognize you.

Apple would be smart to add biometric technology to the iPhone. Fingerprint authentication is a good balance between convenience and security for a mobile device.

Biometric systems are seductive, but the reality isn't that simple. They have complicated security properties. For example, they are not keys. Your fingerprint isn't a secret; you leave it everywhere you touch.

And fingerprint readers have a long history of vulnerabilities as well. Some are better than others. The simplest ones just check the ridges of a finger; some of those can be fooled with a good photocopy. Others check for pores as well. The better ones verify pulse, or finger temperature. Fooling them with rubber fingers is harder, but often possible. A Japanese researcher had good luck doing this over a decade ago with the gelatin mixture that's used to make Gummi bears.

The best system I've ever seen was at the entry gates of a secure government facility. Maybe you could have fooled it with a fake finger, but a Marine guard with a big gun was making sure you didn't get the opportunity to try. Disney World uses a similar system at its park gates—but without the Marine guards.

A biometric system that authenticates you and you alone is easier to design than a biometric system that is supposed to identify unknown people. That is, the question "Is this the finger belonging to the owner of this iPhone?" is a much easier question for the system to answer than "Whose finger is this?"

There are two ways an authentication system can fail. It can mistakenly allow an unauthorized person access, or it can mistakenly deny access to an authorized person. In any consumer system, the second failure is far worse than the first. Yes, it can be problematic if an iPhone fingerprint system occasionally allows someone else access to your phone. But it's much worse if you can't reliably access your own phone—you'd junk the system after a week.

If it's true that Apple's new iPhone will have biometric security, the designers have presumably erred on the side of ensuring that the user can always get in. Failures will be more common in cold weather, when your shriveled fingers just got out of the shower, and so on. But there will certainly still be the traditional PIN system to fall back on.

So ¬Ö can biometric authentication be hacked?

Almost certainly. I'm sure that someone with a good enough copy of your fingerprint and some rudimentary materials engineering capability—or maybe just a good enough printer—can authenticate his way into your iPhone. But, honestly, if some bad guy has your iPhone and your fingerprint, you've probably got bigger problems to worry about.

The final problem with biometric systems is the database. If the system is centralized, there will be a large database of biometric information that's vulnerable to hacking. A system by Apple will almost certainly be local—you authenticate yourself to the phone, not to any network—so there's no requirement for a centralized fingerprint database.

Apple's move is likely to bring fingerprint readers into the mainstream. But all applications are not equal. It's fine if your fingers unlock your phone. It's a different matter entirely if your fingerprint is used to authenticate your iCloud account. The centralized database required for that application would create an enormous security risk.

earlier essay: NSA Surveillance: a Guide to Staying Secure
later essay: The NSA-Reform Paradox: Stop Domestic Spying, Get More Security
categories: Computer and Information Security
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Photo of Bruce Schneier by Per Ervland.

Schneier on Security is a personal website. Opinions expressed are not necessarily those of Co3 Systems, Inc..