In symmetric encryption, what is used to both encrypt and decrypt the data?

• A. The same key
• B. A public key
• C. A random number
• D. A different key for each operation

Answer: (A)

Symmetric encryption uses the same secret key to both lock (encrypt) and unlock (decrypt) the data. The algorithm applies that key to turn plaintext into ciphertext, and the same key again to convert the ciphertext back into plaintext. Because the key must be shared between sender and receiver, secure key distribution and protection are essential.

Choosing a public key is characteristic of asymmetric encryption, which relies on a key pair rather than a single shared secret. A random number by itself isn’t the key used to encrypt and decrypt, though random nonces or initialization vectors may accompany the process. Using a different key for each operation points toward methods that aren’t the standard symmetric approach. The essential idea here is that the same key handles both directions of the process.