Two-time state formalism for quantum eavesdropping

Kieran Flatt, Sarah Croke, Stephen M. Barnett
2018 Physical Review A  
The key piece of knowledge which quantum eavesdroppers can access is the correlation between prior and future events, i.e. the post-selected results of the legitimate preparations and measurements. We present a method for optimising eavesdropping strategies which is closely related to the two-time state formalism, the natural way to analyse such scenarios; it converts the task of optimisation into an eigenvalue problem. Our framework is applied to the familiar BB84 and B92 protocols as well as
more » ... o the largely unexplored three-state scheme, which has a remarkable feature: the best eavesdropping strategy does not extract any information about the sent state.
doi:10.1103/physreva.98.052339 fatcat:nh4yg3ytrnakteavszmlaz7you