When creating a public / private key pair, for which of the following ciphers would a user need to specify
the key strength?

A.
SHA

B.
AES

C.
DES

D.
RSA

Explanation:
RSA (an asymmetric algorithm) uses keys of a minimum length of 2048 bits.
Incorrect Answers:
A: The Secure Hash Algorithm (SHA) was designed to ensure the integrity of a message. SHA is a one-way
hash that provides a hash value that can be used with an encryption protocol. This algorithm produces a
160-bit hash value.
B: Advanced Encryption Standard (AES) has replaced DES as the current standard, and it uses the Rijndael
algorithm. It was developed by Joan Daemen and Vincent Rijmen. AES is the current product used by U.S.
governmental agencies. It supports key sizes of 128, 192, and 256 bits, with 128 bits being the default.
C: 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.

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