Quantum communication is a key enabler of next-generation networks, leveraging quantum entanglement to enable a new class of information exchange. While prior work has focused on the theoretical analysis of communication protocols, their exposure to physical layer side channel analysis remains largely unexplored. In classical systems, side channel analysis has been shown to reveal sensitive information without accessing the underlying data, raising the question of whether similar risks exist in quantum networks. In this work, we investigate whether different quantum communication protocols exhibit distinguishable signatures that can be inferred through passive side channel observations. We consider a threat model in which an observer accesses only a fraction of the optical signal without directly measuring the encoded quantum states. Under this setting, we experimentally examine four representative protocols, namely entanglement distribution, quantum gate sequences, heralded quantum key distribution, and quantum identity authentication, realized on a polarization entangled photon link. Observable physical layer features, including single photon detection statistics and optical power measurements, are collected and used to construct protocol fingerprints. We develop a data-driven framework for protocol identification based on these observations. Our results show that protocol identity can be inferred with accuracy reaching up to 96% under 30:70 sampling configuration/optical tapping, while remaining distinguishable at 10:90 with accuracy ranging from 70-89%. Bell inequality measurements confirm that the sampling/tapping process preserves entanglement, validating the non-destructive nature of the observation model. These findings demonstrate that side channel analysis can expose protocol-level information without disrupting quantum correlations, introducing new security considerations.
Quantum communication is a key enabler of next-generation networks, leveraging quantum entanglement to enable a new class of information exchange. While prior work has focused on the theoretical analysis of communication protocols, their exposure to physical layer side channel analysis remains largely unexplored. In classical systems, side channel analysis has been shown to reveal sensitive information without accessing the underlying data, raising the question of whether similar risks exist in quantum networks. In this work, we investigate whether different quantum communication protocols exhibit distinguishable signatures that can be inferred through passive side channel observations. We consider a threat model in which an observer accesses only a fraction of the optical signal without directly measuring the encoded quantum states. Under this setting, we experimentally examine four representative protocols, namely entanglement distribution, quantum gate sequences, heralded quantum key distribution, and quantum identity authentication, realized on a polarization entangled photon link. Observable physical layer features, including single photon detection statistics and optical power measurements, are collected and used to construct protocol fingerprints. We develop a data-driven framework for protocol identification based on these observations. Our results show that protocol identity can be inferred with accuracy reaching up to 96% under 30:70 sampling configuration/optical tapping, while remaining distinguishable at 10:90 with accuracy ranging from 70-89%. Bell inequality measurements confirm that the sampling/tapping process preserves entanglement, validating the non-destructive nature of the observation model. These findings demonstrate that side channel analysis can expose protocol-level information without disrupting quantum correlations, introducing new security considerations.
Quantum networks can enable distributed computing and sensing. To realize these capabilities securely, quantum identity authentication is essential. Without authentication at the quantum layer, malicious repeaters may retain entanglement instead of performing swapping, enabling man-in-the-middle attacks (MitM) between communicating parties. Authentication mitigates this threat by embedding authentication qubits within data qubits at positions and bases based on a secret key shared a priori. While prior work analyzes security and MitM detection guarantees, physical layer side channel analysis remains unexplored. If an attacker infers protocol stages, it can avoid authentication qubits and extract data qubits, rendering authentication ineffective. To this end, we carry out experimental studies using a quantum communication testbed. A beam splitter is used to tap a portion of the optical signal, allowing the observer to collect side channel data without disrupting the quantum state. We evaluate two sampling settings, where 30% or 10% of the signal is diverted. The collected side channel data includes photon arrival timing and optical power data obtained using a single-photon detector and a power meter. Using this dataset, we extract and engineer features that capture both timing dynamics and signal intensity variations. We then train machine learning models to classify protocol stages based solely on side channel observations. Our results show that protocol-stage inference is feasible with high accuracy, reaching 98% (F1-score 97%) at 30% sampling and 96% (F1-score 94%) at 10% sampling. These findings reveal an overlooked vulnerability and highlight the need for robust designs against side channel inference attacks.
Current communication networks are based on classical physics and classical information-processing. However, for nearly a century, we have known that at its most fundamental level, the universe is governed by the laws of quantum mechanics. With quantum communication, new possibilities arise in our capabilities to transmit and process information which, in many cases, lead to advantages compared to what is classically possible. The entire scope of tasks for which quantum communication can offer improvements has not yet been fully explored, but several quantum protocols are known that can either perform tasks which are impossible with classical resources or can outperform classical protocols. These quantum protocols are well understood from a theoretical point of view, but many of them have never been demonstrated in practice. Thus, in the context of quantum communication, there is a significant gap between theory and experiment that must be removed in order to harness the advantages provided by quantum mechanics in a practical setting. \n \nIn this thesis, we develop a series of tools for developing and testing practical quantum communication protocols. Our main technique is a theoretical reformulation of existing quantum communication protocols that converts them into a form in which they can be demonstrated with existing experimental techniques. More precisely, they can be implemented using only coherent states of light and linear optics circuits while still retaining the crucial properties of the original abstract protocols. We use this result to construct practical protocols for the Hidden Matching problem and quantum fingerprinting. \n \n \nIn the case of quantum fingerprinting, we make a thorough analysis of the role played by experimental errors and show that our practical protocol can still be implemented in the presence of these imperfections. In fact, we report a proof of concept experimental demonstration of a quantum fingerprinting system that is capable of transmitting less information than the best known classical protocol for this problem. Our implementation is based on a modified version of a commercial quantum key distribution system using off-the-shelf optical components over telecom wavelengths, and is practical for messages as large as 100 Mbits, even in the presence of experimental imperfections. \n \nSimilarly, in the context of cryptography, we propose a multiparty quantum signature protocol that can be implemented from any point-to-point quantum key distribution network, proving its security against forging, repudiation and non-transferability. Crucially, since quantum key distribution is already a practical technology, so is this protocol. However, unlike other tasks in quantum communication, there has not been significant theoretical work on establishing a security model for quantum signature schemes. Consequently, we also constructed a security framework for these schemes and proved several properties that these protocols must satisfy in order to achieve their security goals. \n \nFinally, in addition to proposing new practical protocols, we provide a reliable data analysis technique to verify an important property of many quantum communication protocols: the presence of entanglement. Our technique is based on entanglement witnesses and it does not require the specification of a prior distribution nor the assumption of independent measurements. The technique is suitable to be used with nonlinear entanglement witnesses, which we show can be constructed from any linear witness and evaluated from the same experimental data. We also develop numerical tools necessary to employ this approach in practice, rendering the procedure ready to be applied to current experiments. We demonstrate this by analyzing the data of a photonic experiment generating two-photon states whose entanglement is verified with the use of an accessible nonlinear witness.
Optical fibre networks are advancing rapidly to meet growing traffic demands. Security issues, including attack management, have become increasingly important for optical communication networks owing to the vulnerabilities associated with tapping light from optical fibre link. Physical layer security often requires restricting access to the channel and periodic inspection of the link performance. In this thesis, we report how quantum communication techniques can be utilized to detect a physical layer attack. We present an efficient method for monitoring the physical layer security of a high data rate classical optical communication network using a modulated continuous variable quantum signal. We describe the theoretical and experimental underpinnings of this monitoring system, and the monitoring accuracy for different monitored parameters. We analyze its performance in both unamplified and amplified optical links. The technique represents a novel approach in applying quantum signal processing to practical optical communication networks and compares well with classical monitoring methods. We also discuss the challenges in its practical application, its difference with existing quantum key distribution, and its usage in future secure optical transport network planning.
Cryptographic world has faced multiple challenges that are included in encoding and decoding transmitting information into a secure communication channel. Quantum cryptography may be another generation of the cryptography world, which is based on the law of physics. After decades of using the classical cryptography, there is an essential need to move a step forward through the most trusted systems, especially enormous amount of data flows through billions of communicating channels (e.g. The internet), and keeping this transmitting information away from eavesdropping is obligatory. Moreover, quantum cryptography has proved its standing against many weaknesses in the classical cryptography. One of these weaknesses is the ability to copy any type of information using a passive attack without an interruption, which is impossible in the quantum system. Theoretically, several quantum observables are utilized to diagnose an action of one particle. These observables are included in measuring mass, movement, speed, etc. The polarization of one photon occurs normally and randomly in the space. Any interruption that happens during sending of a light will cause a deconstruction of the light polarization. Therefore, particles’ movement in a three-dimensional space is supported by Non-Cloning theory that makes eavesdroppers unable to interrupt a communication system. In case an eavesdropper tried to interrupt a photon, the photon will be destroyed after passing the photon into a quantum detector or any measurement device. In the last decades, many Quantum Key Distribution (QKD) protocols have been created to initiate a secret key during encoding and decoding transmitted data operations. Some of these protocols were proven un-secure based on the quantum attacks that were released early. Even though the power of physics is still active and the Non-Cloning theory is unbroken, some QKD protocols failed during the security measurements. The main reason of the failure is based on the inability to provide the authentication between the end users during the quantum and classical channels. The proposed QKD protocol was designed to utilize some advantages of quantum physics as well as solid functions that are used in the classical cryptography. The authentication is a requirement during different communication channels, where both legitimate parties must confirm their identities before starting to submit data (plain-text). Moreover, the protocol uses most needed scenarios to finish the communication without leaking important data. These scenarios have been approved in existing QKD protocols either by classical or quantum systems. The matrix techniques also are used as a part of the preparation of the authentication key, where the end users communicate by an EPR (related to Einstein, Podolsky, and Rosen theory in 1935) channel. The EPR channel will be supported by an entanglement of particles. If the EPR communication succeeded, transferring the converted plain-text is required. Finally, both end users will have an authenticated secret key, and the submission will be done without any interruption.
A novel approach to secure data transmission, quantum communication draws on fundamental principles of quantum physics. It ensures that the transmitted information is private and accurate. To provide security, quantum networks implement physical constraints such as the no-cloning rule and quantum entanglement. In contrast, computational complexity is employed by classical networks. However, with the proliferation of multiuser quantum networks, identity verification has become more challenging. People with malicious intentions might easily disrupt services in long-distance quantum networks by impersonating legitimate nodes and sharing entangled resources and quantum channels. This highlights the absolute necessity of secure authentication systems tailored to quantum environments. Enhancements to recent quantum authentication systems have been made utilizing techniques that are resistant to quantum computing. Researchers are looking into quantum digital signatures, entanglement-assisted protocols, and quantum key distribution (QKD) authentication to make multi-party communications more secure. In order to prevent attacks where a user establishes a fraudulent identity or account, these strategies can be applied to quantum networks. This study takes a look at current quantum authentication systems and gives them the once-over, focusing on how well they could handle multiple users. The article delves into the evolution of authentication systems to accommodate the distributed model, where nodes can function as senders, receivers, or relays. We aim to strike a compromise between practicality and security in our lightweight, low-latency protocols. Additionally, the paper discusses quantum-specific issues, such as side-channel attacks and device malfunctions, and how authentication techniques can help prevent them. Finally, this study demonstrates that authentication is the critical component of secure quantum communication for multiple users. The most secure quantum key distribution methods are still vulnerable to attacks from inside or outside the system if proper authentication is not in place.
The absolute security of quantum communication protocols relies on a critical premise: all participating parties are legitimate users. Ensuring the legitimacy of participant identities is paramount in complex real-world communication environments. Quantum identity authentication (QIA), in which fundamental principles of quantum mechanics are used to achieve unilateral or mutual authentication between communicating parties, constitutes an indispensable core component for building a comprehensive quantum secure communication system. It holds significant research value in the field of quantum communication. This review employs a comparative classification method to systematically outline the research trajectory of QIA protocols. By categorizing protocols based on the required quantum resources and the types of quantum protocols employed, the advantages and disadvantages of various categories are analyzed in terms of efficiency, security, and practicality. Single-photon protocols require low resources, and they are easy to implement, and compatible with existing optical components, but require high-efficiency single-photon detectors and exhibit weak noise resistance. Entangled-state protocols offer high security and strong resistance to eavesdropping, particularly suitable for long-distance or multi-party authentication. However, they greatly depend on the preparation and maintenance of high-precision, stable multi-particle entanglement sources, resulting in high experimental complexity. Continuous-variable (CV) protocols achieve high transmission efficiency in short-distance metropolitan area networks and are compatible with classical optical communication equipment, making experiments relatively straightforward. Yet, they require high-precision modulation technology and are sensitive to channel loss. Hybrid protocols aim to balance resource efficiency and security while reducing reliance on a single quantum source, but their design is complex and may introduce new attack vectors. Quantum key distribution (QKD) framework protocols embed identity authentication in the key distribution process, making them suitable for scenarios requiring long-term secure key distribution, although they often depend on pre-shared keys or trusted third parties. Quantum secure direct communication (QSDC) framework protocols integrate authentication with secure direct information transmission, offering high efficiency for real-time communication, but requiring high channel quality. Measurement-device-independent QSDC (MDI-QSDC) represents a key development direction that can resist attacks on measurement devices. Quantum teleportation (QT) framework protocols achieves cross-node authentication and unconditional security, making it suitable for quantum relay networks despite its high experimental complexity. The entanglement swapping framework protocol can resist conspiracy attacks and is suitable for multi-party joint scenarios, but it consumes a lot of resources and relies on trusted third party. Ping-pong protocol framework supports dynamic key updates and exhibits strong resistance to eavesdropping, making it suitable for temporary authentication on mobile terminals, although it typically only supports unilateral authentication and requires a bidirectional channel. Subsequently, this review details the latest QIA protocols of our research group, including a multi-party synchronous identity authentication protocol based on Greenberger-Horne-Zeilinger (GHZ) states, and a tripartite QSDC protocol with identity authentication capabilities utilizing polarization-spatial super-coding. The GHZ-based multi-party synchronous authentication protocol leverages the strong correlations inherent in GHZ states to achieve simultaneous authentication among multiple parties. Through a carefully designed two-round decoy-state detection mechanism, it effectively resists both external eavesdropping and internal attacks originating from authenticated users, thereby enhancing the efficiency and security of identity management in large-scale quantum networks. The core innovation of the polarization-spatial super-coding tripartite QSDC protocol lies in its deep integration of the authentication process with information transmission by utilizing the spatial degrees of freedom of single photons. This design accomplishes the identity verification of two senders and the transmission of secret information within a single protocol run, ensuring end-to-end security through a three-stage security check. This “authentication-as-communication” paradigm significantly improves the overall efficiency and practicality of the protocol. Its successful implementation also relies on advancements in quantum memory technology. Finally, the review outlines future research directions for quantum identity authentication and explores its potential applications in quantum communication. The QIA research needs to focus on reducing resource dependency, exploring more efficient protocol designs, further enhancing protocol integration and robustness, prioritizing the development of protocols adaptable to real-world environments, and actively investigating integration with novel scenarios. This comprehensive review aims to provide theoretical research foundations and technical support for the practical development of future quantum identity authentication.