A cryptographic technique that leverages quantum mechanical principles to securely distribute cryptographic keys between two parties. QKD systems typically use individual photons to transmit key information, relying on the principles of quantum mechanics, such as the no-cloning theorem and the observer effect, to detect any eavesdropping attempts. While QKD offers theoretical unconditional security for key distribution, it faces practical challenges in implementation, including the need for specialized hardware, limited distance, and vulnerability to side-channel attacks. Unlike software-based quantum randomness solutions, QKD requires a dedicated quantum channel, usually a fiber optic link or free-space optical path, between the communicating parties.