The iPhone 5s includes Touch ID, Apple's new fingerprint recognition technology. You can use it to unlock your iPhone and authenticate for iTunes Store payments, but Touch ID is raising concerns that criminals will now cut off your finger when they steal your shiny new iPhone. The crooks that want your iPhone are better off leaving your finger intact because Apple's technology is designed to work with live body parts, not severed digits.
Buying an iPhone 5s? Don't worry. Your finger is probably safe.
Touch ID uses the iPhone's Home button to scan your finger or thumb print, and then uses that in lieu of a passcode to unlock the device. Instead of simply scanning print pattern on the outer layer of your skin, Touch ID uses an RF signal to look at the sub dermal layers in your finger and read your print pattern from there. For the system to work, your finger needs to be alive -- which also means it needs to be attached to your hand.
The technology Apple uses comes from Authentec, a company it bought over a year ago for US$365 million. The company was known for its fingerprint scanning technology and Near Field Communication (NFC) tech, too. At the time, there was speculation that Apple was bringing NFC to the iPhone for a digital payment system, but in the end it turned out Apple was far more interested in fingerprint scanning than NFC.
Even though you know your finger is worthless to criminals if it isn't still part of your body, that doesn't mean the bad guys who want your iPhone are savvy to that fact. While there's always a chance that someone could decide to cut off your finger, that's actually a lot of work and there are far easier ways to get past your iPhone's security measures.
The most obvious way to get past your passcode is to use some form of coercion, like the threat of physical harm. That's far quicker than finger cutting, far easier, and ultimately far more effective because it actually works.
Keep in mind, PCs have had less sophisticated fingerprint security for years, and we haven't been overrun with reports of finger thefts going along with stolen laptops. That won't likely change when the iPhone 5s ships, although it's a safe bet the media will be all over the reports if it happens even once.
The idea of stealing your fingerprint goes beyond whether or not it's still attached to your hand. Once your print is scanned, it has to be stored somewhere, and that has plenty of people concerned that it could be stolen in digital form.
The Mac Observer's Charlotte Henry pointed out that the scanned version of your print is stored only on your iPhone in what's called the A7 processor's Secure Enclave. It's encrypted, and doesn't ever leave the chip -- no iCloud backup, and no sharing with other servers or services. Since it's encrypted, too, that makes it even more difficult for anyone to steal your print.
As macabre as it sounds, someone could decide to cut off your finger when they steal your iPhone, but they could do that regardless of whether or not your print has been scanned into your phone. What's more likely is that someone will just grab your iPhone and run, and they'll be stuck with a phone they can't ever use.