Quiz Entry - updated: 2026.07.30
What properties must a cryptographic hash function have?
Deterministic, one-way, fixed-length output, and collision-resistant with an avalanche effect.
| Property | What it means |
|---|---|
| Deterministic | The same input always produces the same hash, every time |
| Fixed length | Output is a constant size no matter how big or small the input is |
| One-way (pre-image resistant) | Easy to compute the hash from the data, but infeasible to recover the data from the hash |
| Avalanche effect | Changing the input even slightly flips the output completely, with no pattern |
| Collision resistant | It is infeasible to find two different inputs that produce the same hash |
Together these make a hash a trustworthy fingerprint. Determinism lets anyone re-check that data matches its hash; one-wayness lets you commit to or verify data without revealing it; the avalanche effect and collision resistance mean nobody can secretly swap the underlying data while keeping the same fingerprint. Remove any one property and the security of the whole chain collapses.
Go deeper:
Cryptographic hash function — Wikipedia — formal treatment of pre-image resistance, collision resistance, and the avalanche effect.