Entanglement-Enhanced Quantum Key Distribution

TL;DR

This paper analyzes the EEQKD protocol, an entanglement-based enhancement of BB84, evaluating its security, key rate, and vulnerabilities, including a paradoxical scenario where EEQKD reduces to BB84.

Contribution

It provides a detailed security analysis of EEQKD, including practical considerations and reveals a paradoxical vulnerability where EEQKD simplifies to BB84.

Findings

EEQKD's secure key rate is affected by qubit loss and noise.

A specific entanglement setting makes EEQKD equivalent to BB84.

EEQKD offers enhanced security against intercept-resend attacks.

Abstract

Quantum key distribution (QKD) allows two spatially separated parties to securely generate a cryptographic key. The first QKD protocol, published by C. H. Bennett and G. Brassard in 1984 (BB84), describes how this is achieved by transmitting individual qubits and exchanging classical authenticated information. Any attempt to eavesdrop on the protocol introduces errors detectable by the legitimate parties. This Licentiate Thesis studies the recently introduced EEQKD protocol which builds on BB84. In EEQKD, the qubits sent individually in BB84 are entangled and thus not directly available to an eavesdropper who is, in this protocol, provided only one-by-one access to the transmission. The maximal information an eavesdropper can gain using a straightforward intercept-resend (IR) attack, is obtained for a given error rate. The secure key generation rate of EEQKD is estimated in practical scenarios including qubit loss and quantum channel noise. In addition, an exquisite vulnerability is exposed: For a particular setting of qubit entanglement, paradoxically proving most useful in the face of an IR attack, EEQKD reduces to BB84. Part of this research has been published in O. Ahonen et al., Physical Review A 78, 032314 (2008).