Small accessible quantum information does not imply security.
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.
König
Robert
R
Centre for Quantum Computation, University of Cambridge, United Kingdom.
Renner
Renato
R
Bariska
Andor
A
Maurer
Ueli
U