Limits on detecting eavesdropper in QKD protocols

Abstract

Quantum key distribution (QKD) protocols form a natural choice for encryption in optical networks. All the QKD protocols use errors caused due to random measurements by Eve to detect her presence. In this paper, we present a fundamental limitation of using such bases to detect an eavesdropper in two QKD protocols - the BB84 and the new quantum Diffie-Hellman key exchange protocol. It is shown that the eavesdropper will go undetected in each exchange in both the protocols at least half the time.