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Abstract

A QKD node in an optical ring network enables distribution of quantum keys between node pairs having neither photon sources nor photon detectors. The QKD node transmits corresponding pulses P.sub.1 and P.sub.2 into the ring network in opposing directions. A first node (Alice) of the pair randomly modulates pulse P1 and a second node (Allie) of the pair randomly modulates pulse P.sub.2, each with phases selected from two encoding bases: B1(0, .pi.) and B2(.pi./2, 3+/2). Node Allie then publicly signals to node Alice and the QKD node to indicate which bases were used for encoding QKD bits in sequence, for example, B1, B2, B2, B1, etc. Node Alice compares the encoding types used by node Allie and publicly signals to nodes Allie and Bob to indicate which encoding types match. The QKD node then deletes all mismatched measurements, and nodes Allie and Alice also delete the corresponding bits. The QKD node then publicly signal to nodes Allie and Alice to indicate the XOR bit string. Nodes Allie and Alice negotiate which is going to do the XOR to their key bit string. After the XORing operation, nodes Allie and Alice form a shifted key and they start quantum error correction and privacy amplification procedures to form a final secret key. Further, the QKD node may modulate a secret key .PHI.s into pulse P.sub.1 before transmission, and into pulse P.sub.2 after receipt, to facilitate security and detection of an eavesdropping attack.

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First Claim