title: Small accessible quantum information does not imply security.
abstract: The security of quantum key distribution is typically defined in terms of the mutual information between the distributed key S and the outcome of an optimal measurement applied to the adversary's system. We show that even if this so-called accessible information is small, the key S might not be secure enough to be used in applications such as one-time pad encryption. This flaw is due to a locking property of the accessible information: one additional (physical) bit of information can increase the accessible information by more than one bit.
authors.affiliation: Centre for Quantum Computation, University of Cambridge, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: König
authors.forename: Renato
authors.initials: R
authors.lastname: Renner
authors.forename: Andor
authors.initials: A
authors.lastname: Bariska
authors.forename: Ueli
authors.initials: U
authors.lastname: Maurer