Quantum Cloning, Eavesdropping and Bell's inequality
  We analyze various eavesdropping strategies on a quantum cryptographic channel. We present the optimal strategy for an eavesdropper restricted to a two-dimensional probe, interacting on-line with each transmitted signal. The link between safety of the transmission and the violation of Bell's inequality is discussed. We also use a quantum copying machine for eavesdropping and for broadcasting quantum information. 
N. Gisin and B. Huttner (Group of Applied Physics, University of   Geneva)