Since the first protocol, proposed by Benette and Brassard in 1984 (BB84), the Quantum Cryptographic(QC) protocols has been studied widely in recent years. It is observed that most of the later QC protocols are variants of BB84 with the intention of addressing one or more problems incurred during the practical implementation of BB84 protocol. Amongst many candidates, SARG04 provides robust performance for the weak coherent pulse implementation of QC. Another follower protocol, KMB09 provides improvement in quantum communication distance between Alice and Bob (the classical communicating parties). Both these protocols are chosen to compete, as they found to be a suitable choice for incorporating QC in existing wireless technology. In this paper we present the performance analysis of these two protocols with respect to protocol efficiency, Quantum Bit Error Rate (QBER) and robustness against eavesdropping.
Since the first protocol, proposed by Benette and Brassard in 1984 (BB84), the Quantum Cryptographic(QC) protocols has been studied widely in recent years. It is observed that most of the later QC protocols are variants of BB84 with the intention of addressing one or more problems incurred during the practical implementation of BB84 protocol. Amongst many candidates, SARG04 provides robust performance for the weak coherent pulse implementation of QC. Another follower protocol, KMB09 provides improvement in quantum communication distance between Alice and Bob (the classical communicating parties). Both these protocols are chosen to compete, as they found to be a suitable choice for incorporating QC in existing wireless technology. In this paper we present the performance analysis of these two protocols with respect to protocol efficiency, Quantum Bit Error Rate (QBER) and robustness against eavesdropping.
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 Q 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.
This thesis explores the critical advancements in quantum communication with a primary focus on the BB84 protocol, the foundation of Quantum Key Distribution (QKD). It delves into the theoretical principles, practical implementation using Qiskit, and performance evaluation through metrics like entropy, Quantum Bit Error Rate (QBER), and efficiency. Comparative analysis with alternative protocols, such as B92 and SARG04, highlights their advantages, limitations, and suitability for real-world applications. The work also addresses challenges like photon number splitting attacks and implementation imperfections, contributing to the development of robust quantum cryptographic systems. By bridging theory and practice, the thesis emphasizes the transformative potential of quantum cryptography in securing communication against both classical and quantum threats. This comprehensive study paves the way for advancements in secure, scalable quantum communication technologies.
We compare the performance of Bennett-Brassard 1984 (BB84) and Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocols, the latter of which was proposed by V. Scarani et al. [Phys. Rev. Lett. 92, 057901 (2004)]. Specifically, in this paper, we investigate the SARG04 protocol with two-way classical communications and the SARG04 protocol with decoy states. In the first part of the paper, we show that the SARG04 scheme with two-way communications can tolerate a higher bit error rate (19.4% for a one-photon source and 6.56% for a two-photon source) than the SARG04 one with one-way communications (10.95% for a one-photon source and 2.71% for a two-photon source). Also, the upper bounds on the bit error rate for the SARG04 protocol with two-way communications are computed in a closed form by considering an individual attack based on a general measurement. In the second part of the paper, we propose employing the idea of decoy states in the SARG04 scheme to obtain unconditional security even when realistic devices are used. We compare the performance of the SARG04 protocol with decoy states and the BB84 one with decoy states. We find that the optimal mean-photon number for the SARG04 scheme is higher than that of the BB84 one when the bit error rate is small. Also, we observe that the SARG04 protocol does not achieve a longer secure distance and a higher key generation rate than the BB84 one, assuming a typical experimental parameter set.
Quantum Key Distribution (QKD) is a technique that enables secure communication between two parties by sharing a secret key. One of the most well-known QKD protocols is the BB84 protocol, proposed by Charles Bennett and Gilles Brassard in 1984. In this protocol, Alice and Bob use a quantum channel to exchange qubits, allowing them to generate a shared key that is resistant to eavesdropping. This paper presents a comparative study of existing QKD schemes, including the BB84 protocol, and highlights the advancements made in the BB84 protocol over the years. The study aims to provide a comprehensive overview of the different QKD schemes and their strengths and weaknesses and demonstrate QKDs working principles through existing simulations and implementations. Through this study, we show that the BB84 protocol is a highly secure QKD scheme that has been extensively studied and implemented in various settings. Furthermore, we discuss the improvements made to the BB84 protocol to enhance its security and practicality, including the use of decoy states and advanced error correction techniques. Overall, this paper provides a comprehensive analysis of QKD schemes, focusing on the BB84 protocol in secure communication technologies.
Quantum cryptography, or, more precisely, quantum key distribution (QKD) allows two distant parties, Alice and Bob, to expand a previously shared secret key by sending quantum states through a quantum channel. The goal here is for Alice and Bob to communicate securely in the presence of an eavesdropper, Eve. The most well-known QKD protocol is the Bennett-Brassard 1984 (BB84) protocol, which has been proved unconditionally secure against any attacks allowed by quantum mechanics. The main advantage of QKD over conventional cryptography is its absolute security. Thus, it is imperative to evaluate the security and performance of QKD protocols and realistic QKD systems. In this thesis, we study the security and performance aspects of QKD in four parts. In the first part, we study the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocol. This protocol differs from the BB84 protocol only in the classical post-processing step and uses the same four quantum states as the BB84 protocol. We compared these two protocols and showed that in typical situations, the classical post-processing software for BB84 should be used in order to have a higher performance. In the second part, we prove the security of a three-state protocol. This protocol is similar to the BB84 protocol in that they share the same three qubit states. In the third part, we consider a practical Trojan horse attack on practical QKD systems implementing the BB84 protocol. The attack works by taking advantage of the finite response time of practical phase modulators to remap the states sent out by the legitimate user, Alice. We showed that if Alice and Bob are unaware of our attack, the final key shared between them can be compromised in some situations. In the fourth part, we consider another type of Trojan horse attack, which is based on mismatch between detection efficiencies of detectors. Practical detectors in QKD systems usually do not have identical efficiencies and an eavesdropper Eve may be able to exploit this efficiency mismatch to steal information about the final secret key. We analyze the security of the attack and show that it is possible for Eve to acquire some information on the final secret key if Alice and Bob are unaware of this attack.
Quantum Key Distribution is a leading-edge cryptographic technology that influences the fundamentals of physics quantum mechanics to enable the secure exchange of encryption keys, establishing peerless levels of confidentiality and aversion against eavesdropping. Quantum Key Distribution (QKD) protocols have been hinged on proceeding in the field of quantum cryptography, guaranteeing safer communication in the existence of adversaries. This paper lays out the comparative survey of some important QKD protocols which are BB84, E91, TF, CV, MDI, COW DPS and SARG04. Each protocol has its unique advantages, characteristics, and limitations, making them appropriate for their different deployment environmental areas. BB84 works on the principle of polarization state and E91 works on entanglement. Both are good at providing robust security under various attack models. To overcome the distance limitations of traditional QKD protocols Twin-Field protocol is a way better that attain more advanced performance in long-distance communication. In Continuous Variable QKD, the requirement of detectors turns out to be lower at the practical levels. Trusted detectors are abolished in MDI-QKD, intensifying the security against the detector side-channel attacks. Coherent One-Way QKD powers up the key rates by employing the encoding in time-bin and phase coherence. Differential Phase Shift-QKD targeted on differential phase shifts for providing robustness against definite types of attack. Finally, Photon number splitting (PNS) attacks get resistance from the SARG04 QKD protocol making it more secure way in a practical framework. In this paper, we compare the performances of these protocols in terms of key rates, error tolerance, security, implementation challenges, advantages, limitations, and feasibility in the real world that are offering perception into their capability for future quantum communication networks.