Which of the following should be used when a business needs a block cipher with minimal key size for
internal encryption?

A.
AES

B.
Blowfish

C.
RC5

D.
3DES

Explanation:
Blowfish is an encryption system invented by a team led by Bruce Schneier that performs a 64-bit block
cipher at very fast speeds. It is a symmetric block cipher that can use variable-length keys (from 32 bits to
448 bits).
Incorrect Answers:
A: For AES there are three ciphers each with a block size of 128 bits, but three different key lengths: 128,
192 and 256 bits.
C: RC5 has a variable block size (32, 64 or 128 bits), key size (0 to 2040 bits) and number of rounds (0 to
255). The original suggested choice of parameters were a block size of 64 bits, a 128-bit key and 12
rounds.
D: Triple-DES (3DES) is a technological upgrade of DES. 3DES is still used, even though AES is the preferred
choice for government applications. 3DES is considerably harder to break than many other systems, and
it’s more secure than DES. It increases the key length to 168 bits (using three 56-bit DES keys).

Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, 6th Edition, Sybex, Indianapolis,
2014, pp. 250, 251, 255-256