Quantum key distribution (QKD) relies on the fundamentals of quantum mechanics to securely share encryption keys between two parties. In QKD, single photon transmissions are used to encode and transmit encryption keys. These photons can either be polarized or encoded in their phase. The receiving party then measures the photons to extract the encryption key without disturbing the quantum state.

To verify that no eavesdropping has occurred during transmission, Quantum Key Distribution takes advantage of the Heisenberg uncertainty principle. This fundamental principle of quantum physics states that certain pairs of measurable properties of a particle, such as its position and momentum, cannot be simultaneously known with perfect precision. Therefore, any attempt to eavesdrop on the transmitted quantum signals would necessarily introduce errors that the communicating parties could detect.

After transmission and measurement, the two parties communicate over a public channel to compare measurement results for a random subset of particles. Any deviations from expected results indicate potential eavesdropping, allowing them to detect the loss of confidentiality and generate a new secure key if needed. The remaining transmission results then become the cryptographic key that can be used to encrypt subsequent communications with perfect secrecy.
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