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IEEE International Conference on Photonics

Security proof of Improved-SARG04 protocol using the same four qubit states

Lizal Iswady Ahmad Ghazali, Ahmad Fauzi Abas, Wan Azizun Wan Adnan, Makhfudzah Binti Mokhtar, Mohd Adzir Mahdi, M. Iqbal Saripan

Published Jul 1, 2010• 3 citations
Publisher

Abstract

We propose a security proof for a new class of quantum key distribution protocol namely Improved-SARG04. This protocol differs from BB84 and SARG04 protocol in the sifting process and provably outperforms those protocols against Photon Number Splitting attack at zero error, with secure transmission distance of 125 km of SSMF.
DOI
10.1109/icp.2010.5604403

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We show that replacing the usual sifting step of the standard quantum-key-distribution protocol BB84 by a one-way reverse reconciliation procedure increases its robustness against photon-number-splitting (PNS) attacks to the level of the SARG04 protocol while keeping the raw key-rate of BB84. This protocol, which uses the same state and detection than BB84, is the m=4 member of a protocol-family using m polarization states which we introduce here. We show that the robustness of these protocols against PNS attacks increases exponentially with m, and that the effective keyrate of optimized weak coherent pulses decreases with the transmission T like T^{1+1/(m-2)}.
The first quantum cryptography protocol, proposed by Bennett and Brassard in 1984 (BB84), has been widely studied in recent years. This protocol uses four states (more precisely, two complementary bases) for the encoding of the classical bit. Recently, it has been noticed that by using the same four states, but a different encoding of information, one can define a protocol which is more robust in practical implementations, specifically when attenuated laser pulses are used instead of single-photon sources [V. Scarani et al., Phys. Rev. Lett. 92, 057901 (2004), referred to as the SARG04 protocol]. We present a detailed study of SARG04 in two different regimes. In the first part, we consider an implementation with a single-photon source: we derive bounds on the error rate QQQ for security against all possible attacks by the eavesdropper. The lower and the upper bound obtained for SARG04 ($Q\ensuremath{\lesssim}10.95%$ and $Q\ensuremath{\gtrsim}14.9%$, respectively) are close to those obtained for BB84 ($Q\ensuremath{\lesssim}12.4%$ and $Q\ensuremath{\gtrsim}14.6%$, respectively). In the second part, we consider a realistic source consisting of an attenuated laser and improve on previous analysis by allowing Alice to optimize the mean number of photons as a function of the distance. The SARG04 protocol is found to perform better than BB84, both in secret-key rate and in maximal achievable distance, for a wide class of Eve's attacks.
Against the backdrop where traditional cryptosystems are threatened by algorithms such as Shor and Grover, Quantum Key Distribution (QKD) technology serves as a next-generation security technology. However, the diversity of its protocols poses challenges to practical research, development, and application. This paper adopts a literature review approach to systematically classify the principles, characteristics, and application scenarios of mainstream protocols, including BB84, SARG04, and MDI-QKD, and also conducts a horizontal comparison of the differences between these protocols in terms of physical implementation, security, key rate, and anti-attack capability. The comparative study reveals that each type of protocol has its own advantages and disadvantages. For instance, BB84 needs to address transmission loss, SARG04 can resist Photon Number Splitting (PNS) attacks, and MDI-QKD is immune to measurement device attacks. Nevertheless, it is still necessary to select a protocol with high adaptability based on factors such as transmission distance, light source type, and environmental noise. This research lays a foundation for the practical application of QKD technology.
Quantum Key Distribution (QKD) is an enabling technology to current modern cryptography which utilizes nature properties of light to transfer key information safely over an unsecured channel. Via this application, both communicating parties can share an identical secret key for their chosen cryptographic scheme in various applications which demand a protection to their highly important message. A designated key bits reconciliation method is known as QKD protocol. The first ever protocol introduced and popularly used is the Bennett and Brassard 1984 (BB84) protocol. However the implementation with current technology has restricted its primary capability to guarantee the security of secret key establishment. As a result, it is vulnerable to Eavesdropping attack. This leads many works on practical protocol and the most significant contribution having used the same setup as the BB84 protocol is the Scarani, Acin, Ribordy and Gisin 2004 (SARG04) protocol. The SARG04 is more robust against photon number splitting attacks and double the BB84 critical transmission distance. Nevertheless SARG04 protocol still has lower percentage of sifted key bit compared to BB84 protocol. Therefore this study has embarked its objectives on identifying and proposing a new QKD protocol which can improve the robustness while allowing higher final key length. The alternative protocol is designed by combining the existing SARG04 decoding with improved SARG04 decoding (ISARG04). Unlike SARG04 which discards any inconclusive result from his measurement, ISARG04 will always accept the non orthogonal state with half probability of error. The robustness of the proposed protocol is simulated based on simple Intercept Resend attack and photon number splitting attacks in quantum key distribution. This new protocol is robust up to two photons per pulse and has an improvement to secure transmissions of bits at higher link loss, up to 26.7 dB. In summary, this work has presented an improved discrete variable protocol which improved the sifted key length and robust to eavesdropping. It is hope that, this contribution might be a breakthrough for near future QKD protocol.