The role of causality in ensuring the ultimate security of relativistic quantum cryptography

One of the central points of quantum information theory is the problem of u ltimate security of quantum cryptography; i.e., the security that is due on ly to the fundamental laws of nature rather than to technical restrictions. It is shown that a relativistic quantum cryptosystem proposed in this pape r is ultimately secure against any eavesdropping attempts. The application of relativistic causality makes it possible to simply prove the security of the cryptosystem. Moreover, because the scheme does not involve collective measurements and quantum codes, it can be experimentally implemented even at the current level of optical fiber technologies. (C) 2001 MAIK "Nauka/In terperiodica".