When two parties communicate with symmetric key encryption, how many keys are used in total to encrypt and decrypt?

• A. One
• B. Two
• C. Four
• D. Eight

Answer: (A)

In symmetric key encryption, the same secret key is used for both encryption and decryption. That means the two parties share one key, and the same key transforms plaintext into ciphertext and then back again to plaintext. There isn’t a separate encryption key and decryption key like in asymmetric systems, where a public key and a private key are used. So the total number of keys involved for the communication is one.