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arXiv:2003.08268

Simplified BB84 quantum key distribution secure against coherent attacks

Yu-Shuo Lu, Hua‐Lei Yin, Zeng‐Bing Chen

Published Mar 18, 2020• 0 citations
arXivHTMLPDF

Abstract

Decoy-state quantum key distribution (QKD) has convincingly been shown the core solution to secure key exchange. While standard BB84 protocol needs to prepare and measure all states of two complementary bases, which seriously restricts its real life applications in photonic integration and high speed system. Fortunately, a simplified BB84, only sending and receiving three states, achieves the same asymptotic secret key rate compared with standard BB84 under coherent attacks. In this work, by skillfully exploiting uncertainty relation for smooth entropies, we provide the finite-key security bounds for decoy-state simplified BB84 QKD against coherent attacks in the universally composable framework. Simulation results show that it can also achieve almost the same performance compared with standard BB84 even the total number of pulses is as low as $10^{8}$. We conclude that simplified BB84 can completely replace standard BB84 to be the best choice for QKD in most common practical scenarios.

DOI
10.48550/arxiv.2003.08268

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Decoy-state quantum key distribution (QKD) has convincingly been shown the core solution to secure key exchange. While standard BB84 protocol needs to prepare and measure all states of two complementary bases, which seriously restricts its real life applications in photonic integration and high speed system. Fortunately, a simplified BB84, only sending and receiving three states, achieves the same asymptotic secret key rate compared with standard BB84 under coherent attacks. In this work, by skillfully exploiting uncertainty relation for smooth entropies, we provide the finite-key security bounds for decoy-state simplified BB84 QKD against coherent attacks in the universally composable framework. Simulation results show that it can also achieve almost the same performance compared with standard BB84 even the total number of pulses is as low as 10810^{8}108. We conclude that simplified BB84 can completely replace standard BB84 to be the best choice for QKD in most common practical scenarios.
Quantum key distribution (QKD) promises provably secure communications. In order to improve the secret key rate, combining a biased basis choice with the decoy-state method is proposed. Concomitantly, there is a basis-independent detection efficiency condition, which usually cannot be satisfied in a practical system, such as the time-phase encoding. Fortunately, this flaw has been recently removed theoretically and experimentally in the four-intensity decoy-state BB84 QKD protocol using the fact that the expected yields of single-photon states prepared in two bases stay the same for a given measurement basis. However, the security proofs do not fully consider the finite-key effects for general attacks. In this work, we provide the rigorous finite-key security bounds in the universally composable framework for the four-intensity decoy-state BB84 QKD protocol. We build a time-phase encoding system with 200 MHz clock to implement this protocol, in which the real-time secret key rate is more than 60 kbps over 50 km single-mode fiber.
The decoy-state Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol is widely regarded as the de facto standard for practical implementations. On the receiver side, passive basis choice is attractive because it significantly reduces the need for random number generators and eliminates the need for optical modulators. Despite these advantages, a finite-key analytical security proof for the decoy-state BB84 protocol, where the basis is chosen passively with a biased probability, has been lacking. In this work, we present a simple analytical finite-key security proof for this setting, yielding a closed-form secret-key rate formula that can be directly evaluated using experimentally accessible parameters. Numerical simulations show that the key rates of passiveand active-measurement implementations are nearly identical, indicating that passive measurement does not compromise key-generation efficiency in practical QKD systems.
Information-theoretical security of quantum key distribution (QKD) has been convincingly proven in recent years and remarkable experiments have shown the potential of QKD for real-world applications. Due to its unique capability of combining high key rate and security in a realistic finite-size scenario, the efficient version of the BB84 QKD protocol endowed with decoy states has been subject of intensive research. Its recent experimental implementation finally demonstrated a secure key rate beyond 1 Mb/s over a 50 km of optical fiber. However, the achieved rate holds under the restrictive assumption that the eavesdropper performs collective attacks. Here, we review the protocol and generalize its security. We exploit a map by Ahrens to rigorously upper bound the hypergeometric distribution resulting from a general eavesdropping. Despite the extended applicability of the new protocol, its key rate is only marginally smaller than its predecessor in all cases of practical interest.
This report reviews two quantum key distribution (QKD) protocols: the BB84 protocol and the measurement device independent (MDI) QKD protocol. The goal of this report is to recreate the security proof of the BB84 protocol, to generate the secret key rate for a practical application of the BB84 protocol, both with and without decoy states, and to review the MDI-QKD protocol and look at the advantages it has for practical QKD. The proof security of the BB84 protocol is done by designing an equivalent theoretical protocol and proving its security by bounding the information of the eavesdropper to an exponentially small number. The best distance over which secret key rate can be generated with the practical model of the BB84 protocol that is presented in this report, is 165 km. This is achieved by employing decoy states and is more than three times as far as the model can achieve without decoy states, which gave a distance of 52 km at best. The zero distance key rate of the model with decoy states is R = 1.21 · 10-2 bits per pulse (bpp), at best. This is an order of magnitude larger than R =1.02 · 10-3 bpp, which is what the model without decoy states could produce. The decoy state method is therefore an improvement for practical QKD. By reviewing the MDI-QKD protocol it can be concluded that because it eliminates the measurement device side channels, it is very useful for practical QKD, since it makes security analysis simpler and more precise. It also necessarily employs decoy states, which improves the secret key rate. MDI-QKD therefore is a promising protocol to use for future quantum communications.
As quantum computing threatens classical cryptography like RSA via Shor's algorithm, Quantum Key Distribution (QKD)—especially BB84—offers physics-based security. BB84 leverages quantum principles: Heisenberg Uncertainty, No-Cloning Theorem, and superposition, shifting from math complexity to unbreakable physical laws using polarized photons for key exchange. The protocol detects eavesdropping through Quantum Bit Error Rate (QBER), showing 25% errors in Intercept-Resend attacks. Key challenges like Photon Number Splitting (PNS) attacks are addressed via decoy states. Compared to B92 and E91, BB84 balances feasibility and security best. Despite issues like signal loss, BB84 provides provably secure communication, restoring trust in a post-quantum world.
In phase-randomized weak coherent pulse (WCP) implementations of Quantum Key Distribution (QKD) BB84 protocol, the decoy method is often used to compensate BB84's vulnerability against photon number splitting (PNS) attacks. However, this typically introduces extra complexities and requirements on experimental devices. In this paper, we are therefore interested in phase-randomized WCP implementations without the decoy method. We examine the performance of three QKD protocols with different classical announcement structures, namely BB84, SARG04, and No Public Announcement of Basis (NPAB) BB84, using numerical security proof techniques. We compare secure key rates of the three protocols in asymptotic and finite-size regimes for lossy and noisy channels. The three protocols show different relative advantages depending on the channel behaviour. Canonical BB84 shows robustness against errors and depolarization, SARG04 demonstrates resilience against high loss channels, and NPAB BB84 shows potential advantages against physical misalignment between QKD devices.