What is "unkeyed cryptography" and what primitives does it include?

Unkeyed cryptography covers primitives that don't require a secret key — like hash functions and random number generators.

The main unkeyed primitives:

• Hash functions — produce a fixed-size "fingerprint" of any input. Used for integrity checks, password storage, digital signatures.
• One-way functions with trapdoor — easy to compute forward, but only reversible if you know the trapdoor (secret). These are the foundation of asymmetric crypto (e.g., RSA).
• One-way functions without trapdoor — truly irreversible. Hash functions are the most common example.
• PRNGs (Pseudo-Random Number Generators) — deterministic algorithms that produce output indistinguishable from true randomness.

Despite being "unkeyed," these primitives are essential building blocks used inside keyed systems.

Go deeper:

• One-way function - easy to compute, hard to invert: the without-trapdoor case.
• Trapdoor function - the with-trapdoor variant that underpins public-key crypto.
• Pseudorandom number generator - the third unkeyed building block.