Why is this so exciting?
There are two reasons this is so exciting. First, this now means you won't have to enter your passcode before you can do simple things like texting. As Apple has said, only about half of iPhone users use a passcode at all, and I suspect most of them use a simple four digit PIN. Your fingerprint is a far more secure option, and putting the reader right in the home button makes it more convenient than swiping your phone to unlock it.
It is yet another example of Apple making security invisible. Over the next few years I think it is safe to say that most iDevices will include a Touch ID sensor, placing strong security into everyone's hands.
But take this a step further. Although a fingerprint alone isn't necessarily more secure than a passcode, combining a fingerprint and a security token counts as strong authentication. Some of you already use your iPhone as a security token with your bank or services like Dropbox or Google Authenticator that send one-time codes to the phone registered with your account.
Now all those services could eventually have the option (depending on Apple) of using both your fingerprint and your device to authenticate you. Apple may be placing strong, biometrics-enabled authentication in the hands of masses of consumers. During Apple's announcement, the company clearly stated that it considers phones to be keys, which indicates it's heading down the path of making your phone, and your fingerprint, the keys to your digital life.
And perhaps your physical life, too, as door locks, home alarms, payment cards, payment systems like Passbook, and other codes and credentials are stored on your phone and made accessible using everything from WiFi and LTE to short-range Bluetooth protocols. Touch ID could be game-changing in the long run, and I'd expect other phone manufacturers to follow that same path, to the point that unlocking your phone with your fingerprint to access online and real world services will someday seem entirely normal.
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