A public key algorithm that does both encryption and digital signature is which of the following?

A.
RSA

B.
DES

C.
IDEA

D.
Diffie-Hellman

Explanation:
RSA, named after its inventors Ron Rivest, Adi Shamir, and Leonard Adleman, is a public key algorithm that is
the most popular when it comes to asymmetric algorithms. RSA is a worldwide de facto standard and can beused for digital signatures, key exchange, and encryption. It was developed in 1978 at MIT and provides
authentication as well as key encryption.
One advantage of using RSA is that it can be used for encryption and digital signatures. Using its one-way
function, RSA provides encryption and signature verification, and the inverse direction performs decryption and
signature generation.
Incorrect Answers:
B: DES is a symmetric block encryption algorithm. It is not a public key algorithm.
C: IDEA is a symmetric block encryption algorithm. It is not a public key algorithm.
D: Diffie-Hellman is used for key distribution. It is not what is described in the question.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 815