Cancellable Biometrics A Case Study In Fingerprints For Kids

iPhone Fingerprint Authentication

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...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.

This essay previously appeared on Wired.com.

EDITED TO ADD: The new iPhone doeshaveafingerprintreader.

Tags: Apple, authentication, biometrics, cell phones, essays, fingerprints, identification, iPhone, scanners

Posted on September 11, 2013 at 6:43 AM • 69 Comments

Biometrics

Biometrics may seem new, but they're the oldest form of identification. Tigers recognize each other's scent; penguins recognize calls. Humans recognize each other by sight from across the room, voices on the phone, signatures on contracts and photographs on driver's licenses. Fingerprints have been used to identify people at crime scenes for more than 100 years.

What is new about biometrics is that computers are now doing the recognizing: thumbprints, retinal scans, voiceprints, and typing patterns. There's a lot of technology involved here, in trying to both limit the number of false positives (someone else being mistakenly recognized as you) and false negatives (you being mistakenly not recognized). Generally, a system can choose to have less of one or the other; less of both is very hard.

Biometrics can vastly improve security, especially when paired with another form of authentication such as passwords. But it's important to understand their limitations as well as their strengths. On the strength side, biometrics are hard to forge. It's hard to affix a fake fingerprint to your finger or make your retina look like someone else's. Some people can mimic voices, and make-up artists can change people's faces, but these are specialized skills.

On the other hand, biometrics are easy to steal. You leave your fingerprints everywhere you touch, your iris scan everywhere you look. Regularly, hackers have copied the prints of officials from objects they've touched, and posted them on the Internet. We haven't yet had an example of a large biometric database being hacked into, but the possibility is there. Biometrics are unique identifiers, but they're not secrets.

And a stolen biometric can fool some systems. It can be as easy as cutting out a signature, pasting it onto a contract, and then faxing the page to someone. The person on the other end doesn't know that the signature isn't valid because he didn't see it fixed onto the page. Remote logins by fingerprint fail in the same way. If there's no way to verify the print came from an actual reader, not from a stored computer file, the system is much less secure.

A more secure system is to use a fingerprint to unlock your mobile phone or computer. Because there is a trusted path from the fingerprint reader to the stored fingerprint the system uses to compare, an attacker can't inject a previously stored print as easily as he can cut and paste a signature. A photo on an ID card works the same way: the verifier can compare the face in front of him with the face on the card.

Fingerprints on ID cards are more problematic, because the attacker can try to fool the fingerprint reader. Researchers have made false fingers out of rubber or glycerin. Manufacturers have responded by building readers that also detect pores or a pulse.

The lesson is that biometrics work best if the system can verify that the biometric came from the person at the time of verification. The biometric identification system at the gates of the CIA headquarters works because there's a guard with a large gun making sure no one is trying to fool the system.

Of course, not all systems need that level of security. At Counterpane, the security company I founded, we installed hand geometry readers at the access doors to the operations center. Hand geometry is a hard biometric to copy, and the system was closed and didn't allow electronic forgeries. It worked very well.

One more problem with biometrics: they don't fail well. Passwords can be changed, but if someone copies your thumbprint, you're out of luck: you can't update your thumb. Passwords can be backed up, but if you alter your thumbprint in an accident, you're stuck. The failures don't have to be this spectacular: a voiceprint reader might not recognize someone with a sore throat, or a fingerprint reader might fail outside in freezing weather. Biometric systems need to be analyzed in light of these possibilities.

Biometrics are easy, convenient, and when used properly, very secure; they're just not a panacea. Understanding how they work and fail is critical to understanding when they improve security and when they don't.

This essay originally appeared in the Guardian, and is an update of an essay I wrote in 1998.

Tags: authentication, biometrics, essays, ID cards, identification, resilience

Posted on January 8, 2009 at 12:53 PM • 62 Comments

Comments

Leave a Reply

Your email address will not be published. Required fields are marked *