Of all biometric modalities, fingerprint has the longest history and the most established infrastructure. Fingerprints are universal, unique, widely acceptable, fairly permanent (they wear and scar, but otherwise stay stable), familiar, and convenient. The biometric is typically registered for authentication systems, like in most smartphones, as well as for establishing official identity in large government-funded databases. The FBI database registers fingerprint biometrics, as does the world’s largest biometric database, India’s Aadhaar program.

In general, modern fingerprint scanners have a FAR of 0.001% and a FRR of 0.1%, which is significantly improved over facial recognition but higher than the next few modalities covered below.

There are a handful of different fingerprint scanner types. I’m going to touch briefly on three: capacitive, optical, and ultrasonic. Ink-and-paper images are still widely collected as well, for example by local police departments, but they won't be covered here except to note their relative inaccuracy. While none is immune to spoofing, they can be good enough. The capacitive scanners in most cell phones are too small to provide any serious security, for example, but they strike a balance between security and convenience.

Capacitive

The system works by using electrical charge to measure the ridges and valleys of the fingerprint to form a 3D model. Because of the proximity required between fingertip and sensor, capacitive scanners won’t work through glass or plastic. They also have trouble with surface grime and oil. They are relatively inexpensive. As previously mentioned, capacitive systems dominate the current market.Capacitive scanners can be spoofed using a 3D model, but that model must be fairly complex in order to fool the liveness tests often built into the systems. They can also be spoofed by similar fingerprints. In order to remain small enough for commercial convenience, scanners often need to register several separate images of a fingerprint, which is compiled into a piecemeal 3D model; users only need to match one of these separate images to be accepted. A study by New York University and Michigan University recently found that generic “masterprints” could be created which would unlock 65% of smartphones. Still, in the absence of a fingerprint reader, many smartphone users might not lock their phones at all, for convenience.

Optical

The system registers a high definition 2D image of the fingerprint. Unlike capacitive scanners, these can be spoofed with 2D images, though spoofers would likely also need to circumvent a liveness test. Optical sensors work through glass and plastic and despite dirt, grime, and oil on the surface of the fingertip. Currently optical sensors control a negligible percentage of the market for consumer products like laptops and smartphones.

Ultrasonic

The system uses soundwaves to form a 3D image of both the surface and subsurface of the fingertip, using technology similar to an ultrasound during a pregnancy. It registers the most raw data of the three types, making it theoretically the most accurate but also greatly increasing the cost. It has fewer problems with surface imperfections like cuts or scars. It is also difficult to spoof, but the higher cost currently restricts its application to businesses concerned enough with security to justify the cost and to high-end personal consumer devices. Ultrasonic sensors control about 1% of the market shares for smartphones. Qualcomm is so far the only company to produce and ship the sensors.


Upsides

Cheap, familiar, broadly-acceptable, and well-established.


Downsides

Fingerprints are strongly associated with criminal background, and not all fingerprinting technologies are equally accurate. Older methods often require rolling and pressing to get a complete image, which produces unpredictable distortions and noise. A 2005 study found that even fingerprint experts employed by the US criminal justice system had only a 44% success rate in matching a set of fingerprints to an individual, despite having all ten fingers and thumbs for comparison. And because of the widespread use of fingerprinting by governments, providing this biometric can be a requirement for exercising important political and economic rights, for example in certain Indian states, or for traveling to certain countries.Fingerprint verification is not accurate enough by itself for secure purposes.


Predictions

Fingerprint technology is well-established and here to stay. Security systems will continue to use it in conjunction with other forms of verification. Government databases, usually especially slow to change, will continue to collect and use fingerprints to establish and verify identity. In the near future smartphones and other consumer goods may move more toward other, more secure or more novel biometric systems, the low cost and convenience of fingerprint sensors will ensure they last a long while yet. Given its security features, ultrasonic should win out against other types in the market as long as its costs can eventually be brought down.

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