2 cissp ® Official Study Guide Eighth Edition

Keystroke Patterns Keystroke patterns
(also known as 
keystroke dynamics
) measure 
how a subject uses a keyboard by analyzing flight time and dwell time. 
Flight time
is how 
long it takes between key presses, and 
dwell time
is how long a key is pressed. Using key-
stroke patterns is inexpensive, nonintrusive, and often transparent to the user (for both use 
and enrollment). Unfortunately, keystroke patterns are subject to wild variances. Simple 
changes in user behavior greatly affect this biometric factor, such as using only one hand, 
being cold, standing rather than sitting, changing keyboards, or sustaining an injury to the 
hand or a finger.
The use of biometrics promises universally unique identification for every person 
on the planet. Unfortunately, biometric technology has yet to live up to this prom-
ise. However, technologies that focus on physical characteristics are very useful for 
authentication.
Biometric Factor Error Ratings
The most important aspect of a biometric device is its accuracy. To use biometrics for 
identification, a biometric device must be able to detect minute differences in information, 
such as variations in the blood vessels in a person’s retina or differences in a person’s veins 
in their palm. Because most people are basically similar, biometric methods often result 
in false negative and false positive authentications. Biometric devices are rated for perfor-
mance by examining the different types of errors they produce.
False Rejection Rate
A false rejection occurs when a valid subject is not authenticated. As 
an example, Dawn has registered her fingerprint and used it to authenticate herself before. 
Imagine that she uses her fingerprint to authenticate herself today, but the system incor-
rectly rejects her fingerprint as valid. This is sometimes called a false negative authentica-
tion. The ratio of false rejections to valid authentications is known as the 
false rejection 
rate (FRR)
. False rejection is sometimes called a 
Type I error
.