# Quantum Key Distribution (QKD) Definition & Meaning

Quantum key distribution (QKD) is the creation and implementation of a quantum encryption key that protects transferred data through quantum physics. Charles Bennett and Gilles Brassard invented the first quantum key distribution protocol in 1984. This protocol is known as BB84 and set the standard for quantum encryption key creation. The principles of quantum physics allow two parties to create a secure channel.

To accomplish quantum key distribution, two parties (Alice and Bob) must first establish an authenticated channel over which they will create the key. Before generating the key, Alice and Bob must interact and authenticate their identities. Quantum key distribution uses subatomic light particles - photons - to create a secret encryption key. Then photons are sent across a cable and are randomly divided by a beam splitter. The remaining photons determine the key, which is now known only to Alice and Bob.

In a Diffie-Hellman key exchange or a four-way handshake process, attackers can spy on the exchange or even interject their own values, taking the place of the legitimate sender (Alice) and tricking the receiving party (Bob) into thinking that they are still interacting with Alice. But establishing a channel using quantum mechanics and using a quantum key means that any eavesdropper will be noticed. If an attacker tries to interrupt the exchange, the nature of the photons will be noticeably disturbed. Alice and Bob will know that someone is attempting to hack their key creation and distribution. This is an added layer of security that traditional methods of encryption key creation do not have.

Quantum cryptography is growing more important because quantum computers can now crack traditional methods of cryptography with ease. In quantum computing, bits are known as quantum bits, or qubits. While bits in traditional computing exist at values of either 0 or 1, qubits do not hold one value consistently. The instability of qubits' value allows a quantum computer to compute many numerical combinations at the same time. While standard encryption keys may use a string of many bits, which would be traditionally difficult for an attacker to learn, quantum computers can crack such a code quickly. Implementing quantum cryptography methods will help protect sensitive data that would otherwise be quite easy for a quantum computer to steal.

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