How the iPhone Fingerprint Scanner Works

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Apple has had a few tricks up its sleeves with every new release of the iPhone. With the iPhone 5s, it was the fingerprint scanner.

Like a lot of other technologies that Apple made popular (graphical user interface and portable hard drives for carrying your music around), the company wasn’t the first to introduce a fingerprint scanner on a phone. Motorola did it in 2011 with their Atrix 4G, and Samsung dabbled in it in 2013. But as always, Apple was the first one to get it right.

Since the 5s, the scanner has been featured as a security feature in the iPad Air2, the iPad Mini 3, and all subsequent releases of the iPhone. It is basically a capacitive scanner hidden behind the Home button, nicely framed by a golden ring that can be used to log-in to the user’s phone. The age -old passcode is still retained, though, and can be used to unlock the phone, bypassing the scanner.


So how does a fingerprint scanner work? Well, there are two kinds. The traditional ones rely on light. These are called ‘œelectro-optical scanners,’ which basically work by shining a light on your finger and comparing the image captured with the one stored in its database. Since they work on an optical image, they are easier to fool and less reliable. Sometimes even a high-resolution photocopy would work.

Apple uses the other technology, which works on ‘œcapacitance.’ Now here, it is important to understand what your fingerprint really is. It is nothing but a unique pattern of ridges and valleys running all over the tip of your finger. For a scanner to work, it need not match the entire pattern. Most scanners work on the basis of matching minutiae, which means storing and checking for the places where ridge lines intersect and where they split. When you swipe your finger on a scanner, your fingerprint is checked against the stored pattern of minutiae, and as long as a sufficient number of points match, it will work to unlock the phone.

How Apple’s fingerprint scanner works.

Apple’s capacitive scanner has an array of capacitive cells embedded under a laser-cut sapphire crystal (to prevent scratching), which respond to your touch. These cells are tiny; I mean really tiny. They are smaller than the width of a typical finger ridge on your thumb. When you touch the scanner, the ridges activate some of the cells in the array, generating a voltage. The valleys, on the other hand, do not come in contact with the cells, and no voltage is generated. The system then creates an ‘œimage’ of your fingerprint by measuring the voltage generated from the various cells and comparing them to the minutiae data stored in its database. Enough matches’”and, violà! Your phone is unlocked!

How safe is it really?

There are three things that make Apple’s fingerprint scanner safe. First of all, your fingerprint data is highly encrypted and stored locally in the device itself and not on an Apple server. This makes hacking into the database and stealing your identity much more difficult.

Secondly, the data stored on your device is only the minutiae information, from which it is impossible to re-create your fingerprint. So even if someone somehow gets access to the data, the print can’t be retrieved.

And lastly, a capacitance-based system is much more reliable and accurate than the traditional scanners, which makes it very difficult to fool it.

There is, however, a catch. Having a passcode allows you to bypass the scanner altogether. Security experts say that the safest system is one that asks for a combination of something you have (fingerprint) and something you know (passcode). But that’s not the way Apple has treaded. Not yet at least.

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One Response


    December 5, 2015 10:55 am

    I was very happy to learn that the new iPhone I was purchasing had fingerprint access. Then, after using the phone for a while, I realized that it still relies on the password as the primary access feature. E.g., if your phone (or iPad) is not used for 48 hours, you cannot access without first entering your password, thus making the fingerprint the secondary access methodology. Same is true when you reboot. What were they thinking?


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