What is a Fingerprint?

Fingerprint authentication is based, obviously enough, on an individual’s fingerprint, but the print is used in an entirely different manner than in forensic fingerprinting. To appreciate the distinction and understand modern fingerprint authentication, we need to look at the anatomy of a fingerprint.

Fingerprints are composed of ridges, the elevated lines of flesh that make up the various patterns of the print, separated by valleys. Ridges form many patterns, including loops, whorls, arches and more. Minutiae are discontinuities in the ridges, which can take the form of various ridge endings, bifurcations (forks), crossovers (intersections), and many others.

Fingerprint authentication is based on a subset of features selected from the overall fingerprint. Data from the overall fingerprint is reduced, using an algorithm application usually unique to each vendor, to extract a dataset based on spatial relationships. For example, the data might be processed to select a certain type of minutiae or a particular series of ridges. The result is a data file that only contains the subset of data points – the full fingerprint is not stored, and cannot be reproduced from the data file. This is in contrast with the forensic fingerprinting that most people associate with the term ‘fingerprinting,’ which is based on the entire fingerprint.

A typical fingerprint authentication data file is less than 1,000 bytes, and is used for one-to-one or one-to-few verification, which takes a few seconds. Modern forensic fingerprinting, on the other hand, creates files on the order of 250Kb for each complete fingerprint; these files are used in large-scale, one-to-many searches with huge databases.

Fingerprint Authentication in Operation

In use, fingerprint authentication is very simple. First, a user enrolls in the system by providing a fingerprint sample. The sensor captures the fingerprint image, which is then interpreted by an algorithm and the representative features extracted to a data file. This process can take place either on a host computer or a local processor (in applications such as a fingerprint door lock). The data file then serves as the user’s individual identification template. During the verification process, the sequence is repeated, generating an extracted feature data file. A pattern-matching algorithm compares the extracted feature data file to the identification template for that user, and the match is either verified or denied. Most products available today can perform these steps in a second or two.