BIOMETRIC DATA UPDATES

Some biometric systems, using technologies based on measuring characteristics and traits that may vary over time, work best when the data base is updated with every use. These are primarily the “what we do” technologies (i.e., voice, signature, and keystroke). Not all systems do this. The action measured by these systems changes gradually over time. The voice changes as people age. It is also affected by changes in weight and by certain health conditions. Signature changes over time are easily documented. For example, look at a signature from Franklin D. Roosevelt at the beginning of his first term as president. Each name and initial is clearly discernable. Then, compare it with his signature in his third term, just 8 years later. To those familiar with it, the strokes and lines are clearly the president’s signature, but to others, they bear no relationship to his name or any other words. Keystroke patterns change similarly over time, particularly depending on typing frequency.

Systems that update the data base automatically average in the current input data into the data base template after the identification transaction is complete. Some also delete an earlier data input, making that data base a moving average. These gradual changes in input data may not affect user identification for many months or years. However, as the data base file and the input data become further apart, increasingly frequent false rejections will cause enough inconvenience that re-enrollment is dictated, which is another inconvenience.

DIFFERENT TYPES OF BIOMETRIC SYSTEMS AND THEIR CHARACTERISTICS

This section describes the different types of biometric systems: fingerprint systems, hand geometry systems, voice pattern systems, retina pattern systems, iris pattern systems, and signature dynamics systems. For each system these characteristics are described: the enrollment procedure and time, the template or file size, the user action required, the system response time, any anticounterfeit method, accuracy, field history, problems experienced, and unique system aspects.

Fingerprint Systems

The information in this section is a compilation of information about several biometric identifying verification systems whose technology is based on the fingerprint.

Data Acquisition

Fingerprint data is acquired when subjects firmly press their fingers against a glass or polycarbonate plate. The fingerprint image is not stored. Information on the relative location of the ridges, whorls, lines, bifurcations, and intersections is stored as an enrolled user data base file and later compared with user input data.

Enrollment Procedure and Time

As instructed, subject enters a 1- to 9-digit PIN on the keypad. As cued, the finger is placed on the reader plate and then removed. A digitized code is created. As cued, the finger is placed and removed four more times for calibration. The total enrollment time required is less than 2 minutes.

Template or File Size

Fingerprint user files are generally between 500 and 1,500 bytes.

User Actions Required

Nearly all fingerprint-based biometrics are verification systems. The user states identification by entering a PIN through a keypad or by using a card reader, then places a finger on the reader plate.

System Response Time

Visual and audible annunciation of the confirmed and not confirmed decision occurs in 5 to 7 seconds.

Accuracy

Some fingerprint systems can be adjusted to achieve a false accept rate of 0.0%. Sandia National Laboratories tests of a top-rated fingerprint system in 1991 and 1993 produced a three-try false reject rate of 9.4% and a crossover error rate of 5%.

Field History

Thousands of units have been fielded for access control and identity verification for disbursement of government benefits, for example.

Problems Experienced

System operators with large user populations are often required to clean sensor plates frequently to remove built-up skin oil and dirt that adversely affect system accuracy.

Unique System Aspects

To avoid the dirt build-up problem, a newly developed fingerprint system acquires the fingerprint image with ultrasound. Claims are made that this system can acquire the fingerprint of a surgeon wearing latex gloves. A number of companies are producing fingerprint-based biometric identification systems.