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

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.
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