What key size is used by the Clipper Chip?

A.
40 bits

B.
56 bits

C.
64 bits

D.
80 bits

Explanation:
The Clipper Chip made use of the Skipjack algorithm, which is a symmetric cipher that uses an 80-bit key.
Incorrect Answers:
A: RC4 is able to use key sizes ranging from 40 bits to 256 bits.
B: DES makes use of a 64-bit key, of which 56 bits make up the true key, and 8 bits are used for parity.
C: DES makes use of a 64-bit key, of which 56 bits make up the true key, and 8 bits are used for parity.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, pp. 800-802,
Conrad, Eric, Seth Misenar, Joshua Feldman, CISSP Study Guide, 2nd Edition, Syngress, Waltham, 2012, p.250