Quantum Cryptography Basics (2026)
Quantum cryptography uses the physics of qubits—not math hardness—to detect eavesdroppers and exchange keys with information-theoretic guarantees. For a quick foundation on qubits and gate models, see How Quantum Computers Work (2026 Edition).
Why it matters in 2026
- Harvest now, decrypt later: attackers store today’s traffic, waiting for future quantum machines to break it.
- Provable eavesdropper detection: measurement disturbs quantum states, exposing interception in real time.
- Complement to Post-Quantum Crypto (PQC): QKD protects key exchange via physics; PQC protects via math. Many enterprises deploy both.
Core building blocks
Qubits & No-Cloning: unknown quantum states cannot be perfectly copied. Any probe introduces errors (QBER) that parties can measure.
Quantum Channel + Classical Channel: photons carry states over fiber/free space; a public authenticated classical link handles sifting, error correction, and privacy amplification.
Flagship protocols
- BB84: prepare-and-measure; sender encodes random bits in rectilinear/diagonal bases.
- E91: entanglement-based; uses Bell-pair correlations for untrusted nodes.
Deployment realities (2026)
- Metro fiber QKD is now mainstream; satellite QKD connects inter-city links.
- Keys per second now sufficient for high-value finance/government networks.
- ETSI/ISO standards, PQC-authenticated channels, and HSM integration are default.