A new approach to quantum cryptography to be called KCQ, keyed communicationin quantum noise, is developed on the basis of quantum detection andcommunication theory for classical information transmission. By the use of ashared secret key that determines the quantum states generated for differentdata bit sequences, the users may employ the corresponding optimum quantummeasurement to decode the data. This gives them a better error performance thanan attacker who does not know the key when she makes her quantum measurement,and an overall generation of a fresh key may be obtained from the resultingadvantage. This principle is illustrated in the operation of a concrete qubitsystem A general information-theoretic description of the overall approach willbe presented, and contrasted with the detection/coding description necessaryfor specific protocols.
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