Police Use a Dead Man’s 3D Printed Finger to Unlock His Phone

[ 3D printers ] [News] The method: use a 3D printer to recreate a dead man’s finger so his phone can be unlocked as usual.

Using a 3D printer to print fingerprints and recreate a dead man’s finger.

In June 2016, Anil Jain, a professor of Computer Science at Michigan State University (USA), was asked by the police to help unlock a phone secured with a fingerprint sensor. The phone belonged to a murder victim, and they needed its data for the investigation. Anil Jain’s method was to use a 3D printer to recreate the dead man’s finger so the phone could be unlocked as usual.

Using a 3D printer to print fingerprints and recreate a dead man’s finger.

Using a 3D printer to print fingerprints and recreate a dead man’s finger.

While trying to unlock the phone, investigators reportedly watched a YouTube video of Anil Jain talking about fingerprint reconstruction techniques, so they turned to him. The police would give him the victim’s fingerprints, which had been collected while the man was still alive.

Using a 3D printer to print fingerprints and recreate a dead man’s finger.

From the 2D fingerprint images, Anil Jain’s team built 3D models and printed them on high-resolution 3D printers to accurately recreate the ridges in the fingerprints. The 3D prints were made of soft plastic. They were then coated with a layer of gold, silver or copper a few micrometers thick (1 micrometer = 0.001 mm) so they could conduct electricity like human skin. A 3D print on its own has no electrical charge to pass information to the fingerprint sensor.

Using a 3D printer to print fingerprints and recreate a dead man’s finger.

Jain also said his work (making 3D prints) is mainly for calibrating and improving fingerprint sensors, not for unlocking phones. He did not say which phone the police asked him to unlock. Besides the iPhone, many other brands now have fingerprint sensors. Each brand builds its sensors differently, so the difficulty of unlocking varies. First, Jain’s team would use the 3D prints to unlock another phone of the same model as the victim’s. Only then would he hand the prints over to the police.

Using a 3D printer to print fingerprints and recreate a dead man’s finger.

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Frequently asked questions

Why do 3D printed fingerprints need a thin metal coating?

Many phone fingerprint sensors are capacitive and only respond to a surface that conducts electricity like human skin. An ultra-thin metal coating makes the plastic print conductive while keeping the fingerprint ridges intact.

What resolution does a printer need to 3D print fingerprints?

Fingerprint ridges are very small, so you need a high-resolution printer, such as resin or material jetting, to reproduce them accurately. Regular FDM printers struggle to show this level of detail.

Is fingerprint security on phones still safe?

Faking a fingerprint requires high-quality fingerprint data, specialized equipment and complex techniques, so it is very hard to do outside a lab. Users can add a password or PIN for extra security.

Besides investigations, what are 3D printed fingerprints used for?

They are mainly used in research to test, calibrate and improve the reliability of biometric sensors. Standard test samples help manufacturers assess how well their devices resist spoofing.

Related services at CT3D Group

• On-demand 3D printing service
• 3D scanning service – high-accuracy 3D scanning
• Custom 3D design service
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