Which term describes a one-way function producing a fixed-length digest?

• A. Encryption
• B. Encoding
• C. Hash Function
• D. Key Exchange

Answer: (C)

A hash function describes a one-way process that takes input data of any size and produces a fixed-length digest. The key ideas are that the output is always the same length, and that the function is easy to compute in the forward direction but hard (practically infeasible) to reverse or to find two inputs that yield the same digest. This fixed-length digest acts as a compact fingerprint of the data, making it useful for integrity checks, digital signatures, and password storage (often with salting).

This differs from encryption, which is designed to be reversible with a key; encoding, which is about transforming data for safe transmission or storage without security guarantees; and key exchange, which focuses on establishing a shared secret rather than producing a digest.