What is a cryptographic hash function?

A one-way function that takes any input and produces a fixed-size 'fingerprint' — the same input always gives the same output, but different inputs give different outputs, and you can't reverse it to find the input A function that converts encrypted data back into its original form A way to generate keys from passwords by hashing them multiple times A mathematical function that checks whether data has been corrupted during transmission

What is a 'collision' in hash function terms and why is it a problem?

When two different inputs produce the same hash output — a problem because an attacker could swap a legitimate file for a malicious one with the same hash, defeating integrity checks When two different users try to register with the same username — a security risk When an encrypted message collides with another in network transmission A rare event where a hash function produces a shorter output than expected

What is 'salting' passwords before hashing and why is it important?

Adding a unique random string to each password before hashing — prevents rainbow table attacks and ensures two users with the same password have different stored hashes Adding a secret ingredient to the hash algorithm to make it proprietary and harder to analyze A method of making passwords longer by adding random characters before storage Encrypting stored password hashes with a second key for extra protection

What is a 'rainbow table attack'?

A precomputed table of passwords and their hashes — attackers look up a stolen password hash in the table to find the original password; defeated by salting An attack that uses multiple colors of spectrum analysis to break cryptographic algorithms A table of all possible encryption keys arranged in a rainbow color pattern for easy lookup An attack tool that tests passwords across a rainbow of different character sets

What is a 'Message Authentication Code' (MAC) and what does it prove?

A hash computed using both the message and a shared secret key — proves to the recipient that the message came from someone who knows the key and wasn't modified in transit A code embedded in messages that allows computers to send themselves encrypted requests An authentication system built into Apple Mac computers A short code attached to messages that reveals the sender's identity without encryption

How does password hashing work in a well-designed login system?

At registration: salt the password, hash it with a slow algorithm (bcrypt, Argon2), store salt + hash. At login: take entered password, apply stored salt, hash, compare to stored hash — never store the plaintext password Encrypt the password with the user's account ID as the key and store the result Hash the password and immediately email the user to confirm their password was hashed Store the password in a separate secure database that only the login system can access

What is a 'zero-knowledge proof'?

A cryptographic protocol that lets one party prove they know a secret (like a password or private key) without revealing the secret itself A proof that contains zero information — used to confirm that nothing happened A type of authentication that requires no knowledge from the user — works automatically A mathematical proof with zero errors — a formally verified cryptographic protocol

What is 'multi-party computation' (MPC) in cryptography?

A cryptographic technique allowing multiple parties to jointly compute a function on their private inputs without any party revealing their inputs to others — 'computing on secrets' Using multiple computers in parallel to speed up encryption calculations A protocol requiring multiple parties to approve each step of a computation Distributing encryption work across many processors for efficiency

What is 'homomorphic encryption'?

Encryption that allows computation on encrypted data without decrypting it — the result, when decrypted, equals the result of performing the same computation on the unencrypted data Encryption that produces the same ciphertext for the same input across different systems An encryption system where the same key works for both 'homo' and 'hetero' key formats Encryption that produces human-readable ciphertext — 'homo' means same as human speech

What is 'authenticated encryption' and why is it the modern standard?

Encryption that simultaneously provides confidentiality (data is secret) and authentication (data hasn't been tampered with) — AES-GCM is the standard, providing both in one operation Encryption that requires you to authenticate (log in) before data can be encrypted Encryption certified by an authentication authority to meet security standards An encryption mode that automatically authenticates the identity of the sender