correction of errors. In feedback error control, only enough additional
information is transmitted so the receiver can identify that an error has
occurred. Choices B and D are both error detection methods but not error
correction methods. Block sum check is an extension of parity check
wherein an additional set of parity bits is computed for a block of
characters. A cyclic redundancy check is a technique wherein a single set
of check digits is generated, based on the contents of the frame, for each
frame transmitted.
612
、
Which of the following applet intrusion issues poses the GREATEST
risk of disruption to an organization?
A
、
A program that deposits a virus on a client machine
B
、
Applets recording keystrokes and, therefore, passwords
C
、
Downloaded code that reads files on a client's hard drive
D
、
Applets opening connections from the client machine
ANSWER:D
NOTE:An applet is a program downloaded from a web server to the client,
usually through a web browser that provides functionality for database
access, interactive web pages and communications with other users. Applets
opening connections from the client machine to other machines on the
network and damaging those machines, as a denial-of-service attack, pose
the greatest threat to an organization and could disrupt business
continuity. A program that deposits a virus on a client machine is
referred to as a malicious attack (i.e., specifically meant to cause harm
to a client machine), but may not necessarily result in a disruption of
service. Applets that record keystrokes, and therefore, passwords, and
downloaded code that reads files on a client's hard drive relate more to
organizational privacy issues, and although significant, are less likely
to cause a significant disruption of service.
613
、
Which of the following message services provides the strongest
evidence that a specific action has occurred?
A
、
Proof of delivery
B
、
Nonrepudiation
C
、
Proof of submission
D
、
Message origin authentication
ANSWER:B
NOTE:Nonrepudiation services provide evidence that a specific action
occurred. Nonrepudiation services are similar to their weaker proof
counterparts, i.e., proof of submission, proof of delivery and message