What is the algorithm used for encryption and decryption?

• A. Encryption
• B. Decryption
• C. Cipher
• D. Plaintext

Answer: (C)

Cipher is the term that names the algorithm that governs how data is turned into ciphertext and then back again. It provides the rules and transformations—the substitutions, permutations, and key-based steps—that enable both the encryption and decryption processes. Encryption and decryption are the two operations that apply that algorithm, while plaintext is simply the readable data before any transformation. So, the best answer is cipher, because it describes the actual method used to perform both directions of data hiding and recovery (with the specific keys and parameters shaping the result). Examples like AES or RSA are ciphers themselves—the underlying algorithms—while encryption and decryption describe applying those rules to data.