title: Quantum cryptography as a retrodiction problem.
abstract: We propose a quantum key distribution protocol based on a quantum retrodiction protocol, known as the Mean King problem. The protocol uses a two way quantum channel. We show security against coherent attacks in a transmission-error free scenario, even if Eve is allowed to attack both transmissions. This establishes a connection between retrodiction and key distribution.
authors.affiliation: Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstrasse 2, 30167 Hannover. albert.werner@itp.uni-hannover.de
authors.forename: A H
authors.initials: AH
authors.lastname: Werner
authors.forename: T
authors.initials: T
authors.lastname: Franz
authors.forename: R F
authors.initials: RF
authors.lastname: Werner