QKD Quantum Key Distribution

Definition:
Quantum Key Distribution (QKD) is a method of secure communication that uses quantum mechanics to generate and distribute random cryptographic keys between two parties. It allows the detection of any third-party attempt to intercept or obtain the key, ensuring the confidentiality of future encrypted communication.

Scientific context:
QKD leverages fundamental quantum principles, such as the no-cloning theorem and measurement-induced disturbance, to detect eavesdropping. When a quantum state is measured, its original state is altered, making any unauthorized interception visible to the communicating parties. QKD does not transmit the message itself, but rather the secret key used to encrypt and decrypt messages.

There are two main families of QKD protocols:

• Discrete-variable QKD (DV-QKD), such as BB84, which encodes information in the polarization or phase of single photons.

• Continuous-variable QKD (CV-QKD), which encodes information in the quadratures of light fields and uses standard telecom components.

Example in practice:

• In a QKD session, Alice and Bob exchange quantum signals to establish a raw key. After sifting, error correction, and privacy amplification, they obtain a shared secret key.

• If an eavesdropper (Eve) attempts to intercept the quantum signals, disturbances in the transmission will increase the quantum bit error rate (QBER), alerting Alice and Bob to the intrusion.

QKD is often used alongside post-quantum cryptography (PQC) to offer layered protection against both classical and quantum threats.

Did you know?
QKD has been successfully demonstrated over optical fiber, free-space, and even satellite links, enabling secure communication over hundreds of kilometers.