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Intrusion detection systems. Refer to the Journal of
Chapter 3, Problem 88E(choose chapter or problem)
Problem 88E
Intrusion detection systems. Refer to the Journal of Research of the National Institute of Standards and Technology (Nov.–Dec. 2003) study of a double intrusion detection system with independent systems, Exercise 3.69 (p. 167). Recall that if there is an intruder, system A sounds an alarm with probability .9, and system B sounds an alarm with probability .95. If there is no intruder, system A sounds an alarm with probability .2, and system B sounds an alarm with probability .1. Now assume that the probability of an intruder is .4. Also assume that under a given condition (intruder or not), systems A and B operate independently. If both systems sound an alarm, what is the probability that an intruder is detected?
3.69 Intrusion detection systems. A computer intrusion detection system (IDS) is designed to provide an alarm whenever an intrusion (e.g., unauthorized access) is being attempted into a computer system. A probabilistic evaluation of a system with two independently operating intrusion detection systems (a double IDS) was published in the Journal of Research of the National Institute of Standards and Technology (November/December 2003). Consider a double IDS with system A and system B. If there is an intruder, system A sounds an alarm with probability .9, and system B sounds an alarm with probability .95. If there is no intruder, the probability that system A sounds an alarm (i.e., a false alarm) is .2, and the probability that system B sounds an alarm is .1. Assume that under a given condition (intruder or not), systems A and B operate independently.
a. Using symbols, express the four probabilities given in the example.
b. If there is an intruder, what is the probability that both systems sound an alarm?
c. If there is no intruder, what is the probability that both systems sound an alarm?
d. Given an intruder, what is the probability that at least one of the systems sounds an alarm?
Questions & Answers
QUESTION:
Problem 88E
Intrusion detection systems. Refer to the Journal of Research of the National Institute of Standards and Technology (Nov.–Dec. 2003) study of a double intrusion detection system with independent systems, Exercise 3.69 (p. 167). Recall that if there is an intruder, system A sounds an alarm with probability .9, and system B sounds an alarm with probability .95. If there is no intruder, system A sounds an alarm with probability .2, and system B sounds an alarm with probability .1. Now assume that the probability of an intruder is .4. Also assume that under a given condition (intruder or not), systems A and B operate independently. If both systems sound an alarm, what is the probability that an intruder is detected?
3.69 Intrusion detection systems. A computer intrusion detection system (IDS) is designed to provide an alarm whenever an intrusion (e.g., unauthorized access) is being attempted into a computer system. A probabilistic evaluation of a system with two independently operating intrusion detection systems (a double IDS) was published in the Journal of Research of the National Institute of Standards and Technology (November/December 2003). Consider a double IDS with system A and system B. If there is an intruder, system A sounds an alarm with probability .9, and system B sounds an alarm with probability .95. If there is no intruder, the probability that system A sounds an alarm (i.e., a false alarm) is .2, and the probability that system B sounds an alarm is .1. Assume that under a given condition (intruder or not), systems A and B operate independently.
a. Using symbols, express the four probabilities given in the example.
b. If there is an intruder, what is the probability that both systems sound an alarm?
c. If there is no intruder, what is the probability that both systems sound an alarm?
d. Given an intruder, what is the probability that at least one of the systems sounds an alarm?
ANSWER:
Solution:
Step 1 of 2:
System A sounds an alarm with probability 0.9, and system B sounds an alarm with probability 0.95, if there is an intruder.
System A sounds an alarm with probability 0.2, and the system B sounds an alarm with probability 0.1, if there is no intruder.
The probability of an intruder is 0.4.
We have to find the probability that an intruder is detected