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Quantum Key Distribution (QKD) is typically associated with the one-time pad because it provides a way of distributing a long shared secret key securely and efficiently (assuming the existence of practical quantum networking hardware). A QKD algorithm uses properties of quantum mechanical systems to let 2 parties agree on a shared, uniformly random string. Algorithms for QKD, such as BB84 provide techniques for determining whether an adversarial party has been attempting to intercept key material, and allow for a shared secret key to be determined with relatively few messages exchanged. In the original BB84 paper, it was proven that the one-time pad, with keys distributed via QKD is a perfectly secure encryption scheme. However, this result does depend on the QKD scheme being implemented correctly in practice. Attacks on real-world QKD systems, do exist. For instance, many systems do not send a single photon per bit of the key because of practical limitations, and an attacker could intercept and measure some of the photons associated with a message, gaining information about the key, while passing along unmeasured photons corresponding to the same bit of the key. Combining QKD with a one-time pad can also loosen the requirements on key reuse. In 1990, Bennet and Brassard showed that if a QKD protocol does not detect that an adversary was trying to intercept an exchanged key, than it can safely be reused while preserving secrecy (this result depends on the message space of the scheme being uniformly random, so it may not be practical).