DEFENSE FRONTIER ANALYSIS OF QUANTUM CRYPTOGRAPHIC SYSTEMS

When a quantum cryptographic system operates in the presence of backgr ound noise, security of the key can be recovered by a procedure called key distillation. A key-distillation scheme effective against so-call ed individual (bitwise-independent) eavesdropping attacks involves sac rifice of some of the data through privacy amplification. We derive th e amount of data sacrifice sufficient to defend against individual eav esdropping attacks in both BB84 and B92 protocols and show in what sen se the communication becomes secure as a result. We also compare the s ecrecy capacity of various quantum cryptosystems, taking into account data sacrifice during key distillation, and conclude that the BB84 pro tocol may offer better performance characteristics than the B92. (C) 1 998 Optical Society of America.