Unconditional security of the Bennett 1992 quantum key-distribution   scheme with strong reference pulse
  We prove the unconditional security of the original Bennett 1992 protocol with strong reference pulse. We show that we may place a projection onto suitably defined qubit spaces before the receiver, which makes the analysis as simple as qubit-based protocols. Unlike the single-photon-based qubits, the qubits identified in this scheme are almost surely detected by the receiver even after a lossy channel. This leads to the key generation rate that is proportional to the channel transmission rate for proper choices of experimental parameters. 
Kiyoshi Tamaki, Norbert L\"utkenhaus, Masato Koashi, Jamie   Batuwantudawe