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Applied Mathematics & Information Sciences

A Necessary Condition for the Security of Coherent-One-Way Quantum Key Distribution Protocol

Mhlambululi Mafu, Adriana Marais, Francesco Petruccione

Published Jun 27, 2014• 9 citations
Publisher

Abstract

The coherent-one-way and the differential-phase-shift protocols ar e two of the most recent practical quantum key distribution protocols for quantum cryptography. These protocols belong to a class of so-called distributed-phase-reference quantum key distribution protocols. While security proofs for some limited attacks exis t, the unconditional security proofs this class of protocol remain unrealised. The existing tools for proving security of protocols ag ainst the most general attacks fail to apply to this class of protocol in a straight forward way. One of the necessary conditions for a quantum key distribution protocol to be secure is the presence of noncommuting measurements. In this paper, the coherent-one-way protocol is formalised, and we describe Bob's measurements by non-commuting POVM elements, showing that this security condition is met.

DOI
10.12785/amis/080612

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The coherent-one-way and the differential-phase-shift protocols ar e two of the most recent practical quantum key distribution protocols for quantum cryptography. These protocols belong to a class of so-called distributed-phase-reference quantum key distribution protocols. While security proofs for some limited attacks exis t, the unconditional security proofs this class of protocol remain unrealised. The existing tools for proving security of protocols ag ainst the most general attacks fail to apply to this class of protocol in a straight forward way. One of the necessary conditions for a quantum key distribution protocol to be secure is the presence of noncommuting measurements. In this paper, the coherent-one-way protocol is formalised, and we describe Bob's measurements by non-commuting POVM elements, showing that this security condition is met.
Abstract Quantum technology can enable secure communication for cryptography purposes using quantum key distribution. Quantum key distribution protocol establishes a secret key between two users with security guaranteed by the laws of quantum mechanics. To define the proper implementation of a quantum key distribution system using a particular cryptography protocol, it is crucial to critically and meticulously assess the device’s performance due to technological limitations in the components used. We perform simulations on the ANSYS Interconnect platform to study the practical implementation of these devices using distributed-phase-reference protocols: differential-phase-shift and coherent-one-way quantum key distribution. Further, we briefly describe and simulate some possible eavesdropping attempts, backflash attack, trojan-horse attack and detector-blinding attack exploiting the device imperfections. The ideal simulations of these hacking attempts show how partial or complete secret key can be exposed to an eavesdropper, which can be mitigated by the implementation of discussed countermeasures.
Distributed-phase-reference quantum key distribution stands out for its easy implementation with present day technology. For many years, a full security proof of these schemes in a realistic setting has been elusive. We solve this long-standing problem and present a generic method to prove the security of such protocols against general attacks. To illustrate our result, we provide lower bounds on the key generation rate of a variant of the coherent-one-way quantum key distribution protocol. In contrast to standard predictions, it appears to scale quadratically with the system transmittance.
We prove the unconditional security of coherent-state-based differential phase shift quantum key distribution protocol (DPSQKD) with block-wise phase randomization. Our proof is based on the conversion of DPSQKD to an equivalent entanglement-distillation protocol where the estimated phase error rate determines the amount of the privacy amplification. The generated final key has a contribution from events where the sender emits two or more photons, indicating the robustness of DPSQKD against photon-number-splitting attacks.
Semi-quantum key distribution protocols are designed to allow two users to establish a secure secret key when one of the two users is limited to performing certain “classical” operations. There have been several such protocols developed recently, however, due to their reliance on a two-way quantum communication channel (and thus, the attacker's opportunity to interact with the qubit twice), their security analysis is difficult and little is known concerning how secure they are compared to their fully quantum counterparts. In this paper we prove the unconditional security of a particular semi-quantum protocol and derive an expression for its key rate, in the asymptotic scenario.
The differential-phase-shift (DPS) and the coherent-one-way (COW) are among the most practical protocols for quantum cryptography, and are therefore the object of fast-paced experimental developments. The assessment of their security is also a challenge for theorists: the existing tools, that allow to prove security against the most general attacks, do not apply to these two protocols in any straightforward way. We present new upper bounds for their security in the limit of large distances ( d ≳50 km with typical values in optical fibers) by considering a large class of collective attacks, namely those in which the adversary attaches ancillary quantum systems to each pulse or to each pair of pulses. We introduce also two modified versions of the COW protocol, which may prove more robust than the original one.