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Quantum key distribution

(also QKD)

Quantum key distribution definition

Quantum key distribution is a secure method of communication with cryptographic protocols that use quantum mechanics. Any attempt to obtain encryption keys or eavesdrop alerts legitimate users, since observing a quantum system disturbs it in a measurable way.

See also: post-quantum cryptography, quantum cryptography, cryptographic key

How quantum key distribution works

  • Generation: The parties use a specialized system to generate a stream of photons (light particles).
  • Encoding: Each photon is randomly encoded with a specific quantum state based on the value of the key bit (either a 0 or 1) to be transmitted.
  • Transmission: One party sends the encoded photons to the other through a communication channel (such as an optical fiber).
  • Measurement: The receiving party randomly measures the quantum states of the photons using specialized detectors, assigning each photon a value of 0 or 1.
  • Comparison: The parties compare a subset of their measurement results over another communication channel — if they match, the quantum key distribution channel is secure. If there are discrepancies, the key exchange process is aborted.
  • Distillation: The parties carry out error correction and privacy amplification protocols to extract the final shared encryption key from the measurement results, eliminating any information that could have been obtained by third parties during the key exchange.
  • Communication: The parties can now apply symmetric encryption algorithms using the shared encryption key to secure their communications.

Real quantum key distribution use cases

  • Protecting financial data
  • Protecting high-value intellectual property
  • Secure communications in the defense sector
  • Protecting healthcare infrastructure
  • Communicating sensitive medical data
  • Preventing outside disruption of critical infrastructure, including utilities