What is a secret value used to encrypt or decrypt data?

• A. Cipher
• B. Key
• C. Ciphertext
• D. Plaintext

Answer: (B)

Encryption relies on a secret value called the key. The key is what controls how the plaintext is transformed into ciphertext and, with the correct key, how that ciphertext is turned back into readable plaintext. The algorithm that performs the transformation is called a cipher, but the secret value itself is the key, not the algorithm. In symmetric systems, the same key encrypts and decrypts; in asymmetric systems, a public key encrypts and a private key decrypts, with the private key kept secret. Since the prompt describes a secret value used to perform encryption or decryption, the term that fits this role is the key.