CompTIA Security Plus Mock Test Q1009

A network stream needs to be encrypted. Sara, the network administrator, has selected a cipher which will encrypt 8 bits at a time before sending the data across the network. Which of the following has Sara selected?

A. Block cipher
B. Stream cipher
C. CRC
D. Hashing algorithm

Correct Answer: A
Section: Cryptography

Explanation:
With a block cipher the algorithm works on chunks of data—encrypting one and then moving to the next.
Example: Blowfish is an encryption system that performs a 64-bit block cipher at very fast speeds.

Incorrect Answers:
B: A stream cipher is used for encrypting data when the size of the data is unknown (such as streaming a movie). The data is encrypted one bit at a time as it is streamed.
C: Cyclic redundancy check (CRC) is used for error-detecting, not for encryption.
D: A hash function is used to map digital data of variable size to digital data of fixed length. A hash function is not used for encryption.

References:
Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, 6th Edition, Sybex, Indianapolis, 2014, pp. 250, 255-256
http://en.wikipedia.org/wiki/Cyclic_redundancy_check