Quantum cryptography: Public key distribution and coin tossing

Abstract

When elementary quantum systems, such as polarized photons, are used to\ntransmit digital information, the uncertainty principle gives rise to novel\ncryptographic phenomena unachievable with traditional transmission media, e.g.\na communications channel on which it is impossible in principle to eavesdrop\nwithout a high probability of disturbing the transmission in such a way as to\nbe detected. Such a quantum channel can be used in conjunction with ordinary\ninsecure classical channels to distribute random key information between two\nusers with the assurance that it remains unknown to anyone else, even when the\nusers share no secret information initially. We also present a protocol for\ncoin-tossing by exchange of quantum messages, which is secure against\ntraditional kinds of cheating, even by an opponent with unlimited computing\npower, but ironically can be subverted by use of a still subtler quantum\nphenomenon, the Einstein-Podolsky-Rosen paradox.\n