What is the effective key size of DES?

A.
56 bits

B.
64 bits

C.
128 bits

D.
1024 bits

Explanation:
DES makes use of a 64-bit key, of which 56 bits represents the true key, and the remaining 8 bits are used for
parity.
Incorrect Answers:
B: DES does make use of a 64-bit key, but the effective key size is 56 bits.
C: International Data Encryption Algorithm (IDEA) produces key that is 128 bits long.
D: RC5 support variable-length key sizes ranging from 0-2040.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, pp. 800, 809, 810