The group, known as the Chaos Computer Club (CCC), demonstrated that a fingerprint of the phone user, photographed from a glass surface, was enough to create a fake finger that could unlock an iPhone 5s secured with TouchID.
The print was first photographed with 2400 dots per inch (dpi) resolution. The resulting image was then cleaned up, inverted and laser printed with 1200 dpi onto a transparent sheet with a thick toner setting. Finally, pink latex milk or white woodglue was smeared into the pattern created by the toner on the transparent sheet.
After it had set, the thin latex print was lifted from the sheet, breathed on to make it a tiny bit moist and then placed onto the sensor to unlock the phone. This process has been used with minor refinements and variations against the vast majority of fingerprint sensors on the market, according to the CCC.