What is the maximum number of different keys that can be used when encrypting with Triple DES?

A.
1

B.
2

C.
3

D.
4

Explanation:
Triple DES (3DES) can use a maximum of three keys.
3DES can work in different modes, and the mode chosen dictates the number of keys used and what functions
are carried out:
DES-EEE3 Uses three different keys for encryption, and the data are encrypted, encrypted, encrypted.
DES-EDE3 Uses three different keys for encryption, and the data are encrypted, decrypted, encrypted.
DES-EEE2 The same as DES-EEE3, but uses only two keys, and the first and third encryption processes
use the same key.
DES-EDE2 The same as DES-EDE3, but uses only two keys, and the first and third encryption processes
use the same key.
Incorrect Answers:
A: A maximum of 3, not 1 different keys can be used when encrypting with Triple DES.
B: A maximum of 3, not 2 different keys can be used when encrypting with Triple DES.
D: A maximum of 3, not 4 different keys can be used when encrypting with Triple DES.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 808