As for security, here's what Samsung says:
"The Galaxy Tab S does not store fingerprints, [only] partial patterns. It only saves the information necessary to recognize the fingerprint through a hardware-based protection mechanism. The information that is required to recognize the fingerprint cannot be sent outside of the device...The information is encrypted using a key value unique to each device. In addition, processing of the information is only conducted inside Trusted Execution Environment protected by a hardware-based mechanism utilizing the unique key value. Thus, the information is comprehensively protected throughout the storage and the processing."
Apple iPhone 5s Touch ID vs. Samsung Galaxy Tab S Scanner: Conclusion
While both Touch ID and the Galaxy Tab S fingerprint scanner may seem like somewhat insignificant features, they're features that their owners will very likely use more than any other. Security has also never been more important, because users today store all kinds of sensitive information on their mobile devices. So passwords and device locks are important, and fingerprint scanners make it simpler to use and remember logins.
Touch ID works better than the Tab S scanner. It's quicker and more responsive; you just need to tap a finger to the sensor to unlock, as opposed to swiping your finger. Touch ID also works in any orientation, so you can hold your device sideways or upside down and it still works.
The Galaxy Tab S fingerprint scanner integrates with more services. Some, though, such as the multi-user mode, are tablet features, so it's difficult to directly compare them to Touch ID features. (The Samsung Galaxy S5 also has a fingerprint scanner.) Touch ID is only available on the iPhone 5s, and Apple's iPad doesn't have a fingerprint unlock feature yet -- though it very likely will in the future.
Is one fingerprint scanner more secure than another? It's hard to tell. The comments from Apple and Samsung are very similar. In both cases, fingerprint data -- not an actual fingerprint -- is stored locally on your device, and it's never sent outside of your smartphone or tablet, according to the companies. The fingerprint data is also encrypted within a secure module, the companies say. There's still risk associated with storing this kind of data, because a Bad Guy could potentially access your device, crack the encryption and steal the fingerprint info. But there's little Apple or Samsung could do in that situation.
Overall, I prefer Touch ID, because the experience is close to seamless. I do wish it integrated with more services, though, and I appreciate the Galaxy Tab S's multi-user and private-mode finger authentication features. Preferences aside, I'm a big fan of both Touch ID and Samsung's finger scanner. I hope to see many more devices equipped with better, fuller-featured fingerprint scanners in the future.
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