Quantenschlüsselverteilungs

Quantenschlüsselverteilung, often abbreviated as QKD, is a secure communication method that uses quantum mechanics to distribute encryption keys. Unlike classical cryptography, which relies on computational difficulty to secure keys, QKD offers information-theoretic security, meaning its security is guaranteed by the laws of physics. The fundamental principle behind QKD is that any attempt to eavesdrop on the quantum channel will inevitably disturb the quantum states being transmitted, alerting the legitimate users to the presence of an intruder.

The most common QKD protocols, such as BB84 and E91, involve sending single photons, each prepared in a specific quantum state, from a sender (Alice) to a receiver (Bob). These states can represent bits of information (e.g., polarization of a photon can represent 0 or 1). Alice randomly chooses a basis to encode each bit, and Bob also randomly chooses a basis to measure each incoming photon. After the transmission, Alice and Bob publicly compare the bases they used for each photon. They keep only the bits where their bases matched, forming a raw key. Any discrepancies in the key are attributed to potential eavesdropping or noise in the channel.

To further enhance security, Alice and Bob perform error correction and privacy amplification procedures on the raw key. Error correction removes inconsistencies, while privacy amplification condenses the key to a shorter, uniformly random sequence, effectively eliminating any partial information an eavesdropper might have gained. The result is a shared secret key that is provably secure against any eavesdropper, even one with unlimited computational power. QKD is a promising technology for future secure communication networks, particularly in contexts where long-term data protection is critical.