Optimization of security costs in nested purification protocol
  We analyse security costs in one segment of nested purification protocol in a large quantum cryptography network, employing the quantum switchers and repeaters. We demonstrate that exponential or even super-exponential grow of entanglement resources occurs in dependence on number of the network switchers. For this reason, an optimization in the nested strategy is suggested, preventing a stronger than the exponential grow of entanglement resources. 
Radim Filip