Accepts an input message of any length and generates a fixed-length output via a one-way operation.

• A. Encryption
• B. Cipher
• C. Hash Function
• D. Signature

Answer: (C)

This item tests hash function properties: it accepts input of any length and outputs a fixed-length digest through a one-way operation. A hash function is designed so you can feed in data of arbitrary size, and you always get a digest of a set length (like 256 bits for SHA-256). It’s easy to compute the digest from the input, but it’s not feasible to reverse the process to recover the original data, which is what “one-way” means here. This distinguishes it from encryption, which transforms data into ciphertext that can be decrypted back to the original message using a key. A cipher/encryption process is reversible and typically tied to a key and sometimes variable-length outputs. A digital signature, while related to integrity and authenticity, is about verifying origin with public-key cryptography and produces a signature value, not a generic fixed-length one-way digest. Thus, the described behavior best matches a hash function.