Why does the news keep talking about Chinese QKD progress?

China's QUESS (Micius) satellite-based QKD demonstrations and Beijing-Shanghai backbone are real engineering achievements. They're nationally strategic — the Chinese government has reasons to invest beyond commercial economics. The technology works; it's just expensive.

Will QKD replace post-quantum cryptography?

No. Different threat models. PQ secures the global internet. QKD secures specific dedicated links. They coexist; PQ is the dominant approach.

Is "Measurement-Device-Independent QKD" worth tracking?

MDI-QKD removes detector-side attacks (a real attack class against early QKD). Marginally better security; same fundamental constraints. Pilot-stage in 2025.

What about Twin-Field QKD?

TF-QKD extends usable range to ~400-600 km without trusted nodes. Reduces but doesn't eliminate the dedicated-fibre requirement. Research-stage; not commercially deployed.

Should we mention QKD in our security architecture documentation?

Mention it in the "considered alternatives" section if asked. Document why post-quantum cryptography (ML-KEM, ML-DSA) was selected for your migration. Auditors won't ding you for not deploying QKD; they will ask for cryptographic-agility plans, which PQ migration provides.

Quantum Key Distribution (QKD) — Hype vs Reality, and Why PQ Cryptography Wins

Read as

Quantum Key Distribution (QKD) uses photonics — single photons over fibre or free-space links — to provably-securely exchange keys, with the security guarantee resting on physics (no-cloning theorem) rather than mathematical hardness. Marketing pitches it as “quantum-secure” and “uncrackable.” Reality: QKD requires dedicated fibre infrastructure (typically < 200 km without trusted repeaters), is expensive, and provides only key exchange — not authentication. For 99% of security teams, post-quantum cryptography (ML-KEM) is the practical answer; QKD remains a specialty technology for narrow use cases.

QKD comes up in board conversations because it sounds compelling — “physics-based security.” Most CISOs need to be able to engage with the marketing without committing to a deployment that will burn budget. This module is the analytical framing.

What QKD actually does

Two parties (Alice and Bob) want to share a secret key. They have a fibre-optic link. Alice sends single photons in randomly-chosen quantum states (e.g., polarisation H, V, +45°, -45°). Bob measures each photon in a randomly-chosen basis. Through a public channel, they reveal which basis they used (not the values), and discard photons where bases differed. The remaining photons constitute the shared key.

If an eavesdropper intercepts photons, by the laws of quantum mechanics (no-cloning theorem), measurement disturbs the state. Alice and Bob detect this disturbance via their statistical comparison and abort the key exchange.

The most-deployed protocol is BB84 (Bennett-Brassard 1984). E91 (Ekert 1991) uses entangled photon pairs; both have variants, both work in production.

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Quantum Key Distribution (QKD) — Hype vs Reality, and Why PQ Cryptography Wins

What QKD actually does

Custom team training + practitioner advisory

Other modules in this track

What is Quantum Computing — Qubits, Superposition, Entanglement (Beginner)

Why Quantum Matters for Cybersecurity — The Post-Quantum Threat in Plain English

Shor’s Algorithm Explained — Why RSA and ECC Will Break