Topic: Cryptography and Network Security
How many keys are needed for encrypted communication among 16 persons using AES encryption assuming unique key is used between any two persons:
- A. 120 keys
- B. 256 keys
- C. 32 keys
- D. 216 keys
Answer: A. 120 keys
Explanation: AES is a symmetric encryption algorithm. If a unique key is used between every possible pair of $N$ persons, the total number of keys required is the number of combinations of 2 chosen from $N$, which is given by $\frac{N(N - 1)}{2}$.
For $N = 16$: $\frac{16 \times 15}{2} = 8 \times 15 = 120$ keys.