Quantum key distribution (QKD) is a secure communication method that implements a cryptographic protocol based on the laws of quantum mechanics, specifically quantum entanglement, the measurement-disturbance principle, and the no-cloning theorem. The goal of QKD is to enable two parties to produce a shared random secret key known only to them, which then can be used to encrypt and decrypt messages. This means, when QKD is correctly implemented, one would need to violate fundamental physical principles to break a quantum protocol. The QKD process should not be confused with quantum cryptography in general.