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Counterfactual quantum key distribution without polarization encoding

Akshata Shenoy H., R. Srikanth, Srinivas Talabattula

Published Jan 1, 2013• 4 citations
OpenAlex

Abstract

In counterfactual quantum key distribution (QKD), two remote parties can share a secure \nsecret random key even without transmission of a physical particle (a non-vacuum pulse) through the \nchannel. A QKD scheme is proposed which is counterfactual in one of the bits, and in which the secret bits \nare not encoded in the polarization, but in the joint action of Alice and Bob. On the conceptual level, our \nscheme throws new light on the origin of security in counterfactual cryptography. On the practical side, \nnon-polarization encoding makes it robust against certain trojan horse attacks. We study the the general \nphoton-number preserving incoherent attack in detail.

Related papers

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Communications in Theoretical Physics•Jan 1, 2013•3 citations
In counterfactual quantum key distribution (QKD), two remote parties can share a secure \nsecret random key even without transmission of a physical particle (a non-vacuum pulse) through the \nchannel. A QKD scheme is proposed which is counterfactual in one of the bits, and in which the secret bits \nare not encoded in the polarization, but in the joint action of Alice and Bob. On the conceptual level, our \nscheme throws new light on the origin of security in counterfactual cryptography. On the practical side, \nnon-polarization encoding makes it robust against certain trojan horse attacks. We study the the general \nphoton-number preserving incoherent attack in detail.
In counterfactual quantum key distribution (QKD), two remote parties can securely share random polarization-encoded bits through the blocking rather than the transmission of particles. We propose a semi-counterfactual QKD, i.e. , one where the secret bit is shared, and also encoded, based on the blocking or non-blocking of a particle. The scheme is thus semi-counterfactual and not based on polarization encoding. As with other counterfactual schemes and the Goldenberg-Vaidman protocol, but unlike BB84, the encoding states are orthogonal and security arises ultimately from single-particle non-locality. Unlike any of them, however, the secret bit generated is maximally indeterminate until the joint action of Alice and Bob. We prove the general security of the protocol, and study the most general photon-number–preserving incoherent attack in detail.
\n It is interesting that counterfactual quantum cryptography protocols allow two remotely separated parties to share a secret key without transmitting any signal particles. Generally, these protocols, expected to provide security advantages, base their security on a translated no-cloning theorem. Therefore, they potentially exhibit unconditional security in theory. In this letter, we propose a new Trojan horse attack, by which an eavesdropper Eve can gain full information about the key without being noticed, to real implementations of a counterfactual quantum cryptography system. Most importantly, the presented attack is available even if the system has negligible imperfections. Therefore, it shows that the present realization of counterfactual quantum key distribution is vulnerable.\n
Recently, a ``counterfactual'' quantum-key-distribution scheme was proposed by T.-G. Noh [Phys. Rev. Lett. 103, 230501 (2009)]. In this scheme, two legitimate distant peers may share secret keys even when the information carriers are not traveled in the quantum channel. We find that this protocol is equivalent to an entanglement distillation protocol. According to this equivalence, a strict security proof and the asymptotic key bit rate are both obtained when a perfect single-photon source is applied and a Trojan horse attack can be detected. We also find that the security of this scheme is strongly related to not only the bit error rate but also the yields of photons. And our security proof may shed light on the security of other two-way protocols.
Abstract To save quantum resources and improve efficiency, this article proposes an efficient counterfactual quantum privacy query protocol. Counterfactual quantum privacy query refers to the identification of secure detection and key screening based on the detector's response results without the actual transmission of quantum information between user Bob and database Alice. Alice completes key transmission through a counterfactual device, while Bob measures the photon's polarization with a probability of 1/2 to obtain the encoded classical information, followed by traditional post-processing and privacy query operations. Additionally, to withstand the noise impact during the communication process, a modified counterfactual QKD protocol proposed by Rao (2021) is utilized, where communication parties randomly select a quantum bit flip with a specified probability \textit{f}, and then complete the quantum privacy query.
We propose a new counterfactual quantum cryptography protocol concerning about distributing a deterministic key. By adding a controlled blocking operation module to the original protocol [T.G. Noh, Phys. Rev. Lett. 103 (2009) 230501 ], the correlation between the polarizations of the two parties, Alice and Bob, is extended, therefore, one can distribute both deterministic keys and random ones using our protocol. We have also given a simple proof of the security of our protocol using the technique we ever applied to the original protocol. Most importantly, our analysis produces a bound tighter than the existing ones.