Cryptanalysis and Improvement of a Multi-User Quantum Communication Network Using χ-Type Entangled States

摘要

The security of a multi-user quantum communication network protocol using χ-type entangled states (Chang et al., J. Korean Phys. Soc. 61:1-5, 2012) is analyzed. We find that, by using one χ-type state in this protocol, two participants can only share 2 bits of information, not 4 bits as the authors stated. In addition, we give a special attack strategy by which an eavesdropper can elicit half of the secret information without being detected. Finally, we improve the protocol to be secure against all the present attacks.