Which of the following are restricted to 64-bit block sizes? (Select TWO).

A.
PGP

B.
DES

C.
AES256

D.
RSA

E.
3DES

F.
AES

Explanation:
B: The Data Encryption Standard (DES) has been used since the mid-1970s. It was the primary standard
used in government and industry until it was replaced by AES. It’s based on a 56-bit key and has several
modes that offer security and integrity. It is now considered insecure because of the small key size.
E: 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).
Incorrect Answers:
A: International Data Encryption Algorithm (IDEA) was developed by a Swiss consortium. It’s an algorithm
that uses a 128-bit key.This product is similar in speed and capability to DES, but it’s more secure. IDEA is used in Pretty Good
Privacy (PGP), a public domain encryption system used by many for email.
C: AES256 (also often written as AES-256) uses 256 bits instead of 128.
D: RSA is not restricted to 64-bit keys. 1024 and 2048 bit keys can be used, for example.
F: AES supports key sizes of 128, 192, and 256 bits, with 128 bits being the default.

Dulaney, Emmett and Chuck Eastton, CompTIA Security+ Study Guide, 6th Edition, Sybex, Indianapolis,
2014, pp. 250, 251, 255-256, 272-273