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Commonly confused · Security Fundamentals & Crypto

Post-Quantum Cryptography vs Quantum Key Distribution: What's the Difference?

Post-quantum cryptography is classical math-based algorithms designed to resist quantum computer attacks, running on today's hardware. Quantum key distribution uses quantum physics properties of photons to exchange keys and detect eavesdropping, but requires specialized optical hardware.

Post-Quantum Cryptography (PQC)

Full definition
vs

Quantum Key Distribution (QKD)

Full definition
Post-Quantum CryptographyQuantum Key Distribution
BasisHard math problems (lattices, hashes, codes)Quantum physics (photon states)
HardwareRuns on existing computersRequires dedicated quantum optical links
DistanceUnlimited, works over the internetLimited (typically ~100 km over fiber without trusted nodes)
ExamplesML-KEM (Kyber), ML-DSA (Dilithium), SLH-DSA (SPHINCS+)BB84 protocol
ProvidesKey exchange and signaturesKey exchange only, no authentication by itself
Standards statusNIST standardized FIPS 203, 204, 205 in 2024Niche, not recommended by NSA/NCSC for general use
Remember it

PQC is new math for old machines; QKD is new physics for new wires.

Exam tip

Questions on harvest-now-decrypt-later threats usually want migration to post-quantum algorithms. Know that symmetric AES-256 and SHA-384+ remain acceptable, while RSA and ECC must be replaced.

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