What are hash functions used for?

• A. Providing message integrity
• B. Encrypting messages
• C. Generating encryption keys from passwords
• D. Signatures

Answer: (A)

Hash functions give you a fingerprint of data. The main use is providing message integrity: you can detect if a message was altered by recomputing its hash and comparing it to the original. They take input of any length and produce a fixed-size digest; they’re deterministic, so the same input always yields the same digest, and even a tiny change in the input changes the digest drastically. This makes tampering easy to spot. Hashes don’t hide content, so they’re not encryption. Generating encryption keys from passwords is a different process (password-based key derivation). Signatures involve hashing as a step, but the hash function’s role is to create a compact representation to be signed; the primary use described here is ensuring integrity.