The equation used to calculate the total number of symmetric keys (K) needed for a group of users (N) to
communicate securely with each other is given by which of the following?

A.
K(N – 1)/ 2

B.
N(K – 1)/ 2

C.
K(N + 1)/ 2

D.
N(N – 1)/ 2

Explanation:
The equation employed to determine the required number of symmetric keys is N(N – 1)/2.
Incorrect Answers:
A, B, C: These equations are not valid for calculating the required number of symmetric keys.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 782