Touch ID patent applications reveal how Apple uses "Secure Enclave" in iPhone 5s' A7 chip for fingerprint sensor
Touch ID patents reveal how Apple uses 'Secure Enclave' in iPhone 5s' A7 chip for fingerprint sensor After scanning your finger for the first time, Apple stores a mathematical representation of your fingerprint by running it through a series of irreversible mathematical functions. That is, given the final result of this mathematical process, no one would be able to reconstruct the original fingerprint, thus preventing any misuse of your fingerprint from a compromised iPhone.
From Patently Apple:
Apple’s invention includes a process of collapsing the full maps into a sort of checksum, hash function, or histogram. For example, each encrypted ridge map template can have some lower resolution pattern computed and associated with the ridge map. One exemplary pattern could be a histogram of, e.g., the most common angles (e.g., a 2 dimensional (2D) array of common angles). The exemplary pattern could include in each slot an average value over a respective vector of the map. The exemplary pattern could include in each slot a sum of the values over a respective vector of the map. The exemplary pattern could include the smallest or largest value within a respective vector of the map, or could be a difference between a largest and a smallest value within the respective vector of the map.
Touch ID’s aesthetic treatments have been included as well, as the patent details “an ink assembly…printed on the lens” that “has the effect that the otherwise-translucent button can be made opaque, so the elements of the fingerprint recognition sensor are not immediately visible to the user.”