The advent of quantum key distribution (QKD) has revolutionized secure communication by providing unconditional security, unlike classical cryptographic methods. However, its effectiveness relies on robust identity authentication, as vulnerabilities in the authentication process can cause a compromise with the security of the entire communication system. Over the past three decades, numerous quantum identity authentication (QIA) protocols have been proposed. This thesis first presents a chronological review of these protocols, categorizing them based on quantum resources and computational tasks involved while analyzing their strengths and limitations. Subsequently, by recognizing inherent symmetries present in the existing protocols, we design novel QIA schemes based on secure computational and communication tasks. Specifically, this work introduces a set of new QIA protocols that utilize controlled secure direct quantum communication. The proposed scheme facilitates mutual authentication between two users, Alice and Bob, with assistance from a third party, Charlie, using Bell states. A comprehensive security analysis demonstrates its robustness against impersonation, intercept-res
The rapid development of quantum computers and sensors urges for the development of a quantum Internet capable of transmitting quantum bits over long distances. Photons used for quantum data transfer are fragile over time and sensitive to their environment, so that they cannot be directly used over long distances. To remedy this problem, long distance paths are segmented into shorter links and entangled pairs of photons are distributed over these links and swapped to create end-to-end entangled pairs over long distances, eventually used for teleportation. In this paper, we develop an existing protocol taking account of fidelity and imperfect memories. We shorten the execution time and thus increase its link success probability creating the so-called Locally Heralded Distribution (LHD). It turns out that the proposed protocol outperforms some previous protocols. We benchmark through simulation the performances of protocols considered in this paper by using a blind entanglement protocol as a baseline.
This paper provides a preparatory introduction to torsors, written with a view toward later applications in the author's work. Rather than aiming at a comprehensive survey, the exposition focuses on those aspects of torsors that are most useful for understanding torsor-based reasoning: group actions, orbits, free transitive actions, the absence of a canonically chosen origin, and the interpretation of group elements as transports between points. After developing the basic definition and several elementary examples, we emphasize a central theme: torsors are not only characterized abstractly by free transitive group actions, but also arise naturally as objects obtained by gluing local trivial pieces by means of transition data satisfying cocycle conditions. A brief optional section indicates a sheaf- and topos-theoretic perspective. In the final part, we explain how these ideas prepare the ground for later conceptual applications, including aspects of $Σ$-protocols.
One relevant aspect in the development of the Semantic Web framework is the achievement of a real inter-agents communication capability at the semantic level. The agents should be able to communicate and understand each other using standard communication protocols freely, that is, without needing a laborious a priori preparation, before the communication takes place. For that setting we present in this paper a proposal that promotes to describe standard communication protocols using Semantic Web technology (specifically, OWL-DL and SWRL). Those protocols are constituted by communication acts. In our proposal those communication acts are described as terms that belong to a communication acts ontology, that we have developed, called CommOnt. The intended semantics associated to the communication acts in the ontology is expressed through social commitments that are formalized as fluents in the Event Calculus. In summary, OWL-DL reasoners and rule engines help in our proposal for reasoning about protocols. We define some comparison relationships (dealing with notions of equivalence and specialization) between protocols used by agents from different systems.
This paper provides a preparatory introduction to sheaves and topoi, written as a conceptual continuation of the author's earlier introduction to torsors and as preparatory background for the author's arXiv paper \emph{Grothendieck Topologies and Sheaf-Theoretic Foundations of Cryptographic Security:\ Attacker Models and $Σ$-Protocols as the First Step}~\cite{InoueSecurity}. Rather than attempting an encyclopedic survey of all of topos theory, the exposition develops those parts of the subject that are most relevant for passing from torsor-based local-to-global reasoning to sheaf-theoretic and topos-theoretic reasoning: Grothendieck topologies, sheaves, torsors over a site, descent, sheaf topoi, elementary topoi, Cartesian closed structure, subobject classifiers, and internal logic. The goal is not merely motivational. We try to develop enough genuine topos theory that the reader can understand, not only heuristically but structurally, why the later cryptographic framework of~\cite{InoueSecurity} uses Grothendieck topologies and sheaf-theoretic language. To make the note more self-contained, we also include substantial appendices on basic category theory, Yoneda's lemma, limits and
Cryptographic security is traditionally formulated using game-based or simulation-based definitions. In this paper, we propose a structural reformulation of cryptographic security based on Grothendieck topologies and sheaf theory. Our key idea is to model attacker observations as a Grothendieck site, where covering families represent admissible decompositions of partial information determined by efficient simulation. Within this framework, protocol transcripts naturally form sheaves, and security properties arise as geometric conditions. As a first step, we focus on $Σ$-protocols. We show that the transcript structure of any $Σ$-protocol defines a torsor in the associated topos of sheaves. Local triviality of this torsor corresponds to zero-knowledge, while the absence of global sections reflects soundness. A concrete analysis of the Schnorr $Σ$-protocol is provided to illustrate the construction. This sheaf-theoretic perspective offers a conceptual explanation of simulation-based security and suggests a geometric foundation for further cryptographic abstractions.
In programming, protocols are everywhere. Protocols describe the pattern of interaction (or communication) between software systems, for example, between a user-space program and the kernel or between a local application and an online service. Ensuring conformance to protocols avoids a significant class of software errors. Subsequently, there has been a lot of work on verifying code against formal protocol specifications. The pervading approaches focus on distributed settings involving parallel composition of processes within a single monolithic protocol description. However we observe that, at the level of a single thread/process, modern software must often implement a number of clearly delineated protocols at the same time which become dependent on each other, e.g., a banking API and one or more authentication protocols. Rather than plugging together modular protocol-following components, the code must re-integrate multiple protocols into a single component. We address this concern of combining protocols via a novel notion of 'interleaving' composition for protocols described via a process algebra. User-specified, domain-specific constraints can be inserted into the individual pr
Quantum cryptography is now considered as a promising technology due to its promise of unconditional security. In recent years, rigorous work is being done for the experimental realization of quantum key distribution (QKD) protocols to realize secure networks. Among various QKD protocols, coherent one way and differential phase shift QKD protocols have undergone rapid experimental developments due to the ease of experimental implementations with the present available technology. In this work, we have experimentally realized optical fiber based coherent one way and differential phase shift QKD protocols at telecom wavelength. Both protocols belong to a class of protocols named as distributed phase reference protocol in which weak coherent pulses are used to encode the information. Further, we have analyzed the key rates with respect to different parameters such distance, disclose rate, compression ratio and detector dead time.
One relevant aspect in the development of the Semantic Web framework is the achievement of a real inter-agents communication capability at the semantic level. Agents should be able to communicate with each other freely using different communication protocols, constituted by communication acts. For that scenario, we introduce in this paper an efficient mechanism presenting the following main features: - It promotes the description of the communication acts of protocols as classes that belong to a communication acts ontology, and associates to those acts a social commitment semantics formalized through predicates in the Event Calculus. - It is sustained on the idea that different protocols can be compared semantically by looking to the set of fluents associated to each branch of the protocols. Those sets are generated using Semantic Web technology rules. - It discovers the following types of protocol relationships: equivalence, specialization, restriction, prefix, suffix, infix and complement_to_infix.
The cost of distributed quantum operations such as the telegate and teledata protocols is high due to latencies from distributing entangled photons and classical information. This paper proposes an extension to the telegate and teledata protocols to allow for asynchronous classical communication which hides the cost of distributed quantum operations. We then discuss the benefits and limitations of these asynchronous protocols and propose a potential way to improve these asynchronous protocols using nonunitary operators. Finally, a quantum network card is described as an example of how asynchronous quantum operations might be used.
Feasible interpolation is a general technique for proving proof complexity lower bounds. The monotone version of the technique converts, in its basic variant, lower bounds for monotone Boolean circuits separating two NP-sets to proof complexity lower bounds. In a generalized version of the technique, dag-like communication protocols are used instead of monotone Boolean circuits. We study three kinds of protocols and compare their strength. Our results establish the following relationships in the sense of polynomial reducibility: Protocols with equality are at least as strong as protocols with inequality and protocols with equality have the same strength as protocols with a conjunction of two inequalities. Exponential lower bounds for protocols with inequality are known. Obtaining lower bounds for protocols with equality would immediately imply lower bounds for resolution with parities (R(LIN)).
We introduce state-of-the-art protocols to distill indistinguishable photons, reducing distinguishability error rates by a factor of $n$, while using a modest amount of resources scaling only linearly in $n$. Our resource requirements are both significantly lower and have fewer hardware requirements than previous works, making large-scale distillation experimentally feasible for the first time. This efficient reduction of distinguishability error rates has direct applications to fault-tolerant linear optical quantum computation, potentially leading to improved thresholds for photon loss errors and allowing smaller code distances, thus reducing overall resource costs. Our protocols are based on Fourier transforms on finite abelian groups, special cases of which include the discrete Fourier transform and Hadamard matrices. This general perspective allows us to unify previous results on distillation protocols and introduce a large family of efficient schemes. We utilize the rich mathematical structure of Fourier transforms, including symmetries and related suppression laws, to quantify the performance of these distillation protocols both analytically and numerically. Finally, our work
Cooperative hybrid-ARQ (HARQ) protocols, which can exploit the spatial and temporal diversities, have been widely studied. The efficiency of cooperative HARQ protocols is higher than that of cooperative protocols, because retransmissions are only performed when necessary. We classify cooperative HARQ protocols as three decode-and-forward based HARQ (DF-HARQ) protocols and two amplified-and-forward based (AF-HARQ) protocols. To compare these protocols and obtain the optimum parameters, two unified frameworks are developed for protocol analysis. Using the frameworks, we can evaluate and compare the maximum throughput and outage probabilities according to the SNR, the relay location, and the delay constraint for the protocols.
Security protocols are building blocks in secure communications. They deploy some security mechanisms to provide certain security services. Security protocols are considered abstract when analyzed, but they can have extra vulnerabilities when implemented. This manuscript provides a holistic study on security protocols. It reviews foundations of security protocols, taxonomy of attacks on security protocols and their implementations, and different methods and models for security analysis of protocols. Specifically, it clarifies differences between information-theoretic and computational security, and computational and symbolic models. Furthermore, a survey on computational security models for authenticated key exchange (AKE) and password-authenticated key exchange (PAKE) protocols, as the most important and well-studied type of security protocols, is provided.
Determining if two protocols can be securely composed requires analyzing not only their additive properties but also their destructive properties. In this paper we propose a new composition method for constructing protocols based on existing ones found in the literature that can be fully automatized. The additive properties of the composed protocols are ensured by the composition of protocol preconditions and effects, denoting, respectively, the conditions that must hold for protocols to be executed and the conditions that hold after executing the protocols. The non-destructive property of the final composed protocol is verified by analyzing the independence of the involved protocols, a method proposed by the authors in their previous work. The fully automatized property is ensured by constructing a rich protocol model that contains explicit description of protocol preconditions, effects, generated terms and exchanged messages. The proposed method is validated by composing 17 protocol pairs and by verifying the correctness of the composed protocols with an existing tool.
We present two abstractions for designing modular state machine replication (SMR) protocols: trees and turtles. A tree captures the set of possible state machine histories, while a turtle represents a subprotocol that tries to find agreement in this tree. We showcase the applicability of these abstractions by constructing crash-tolerant SMR protocols out of abstract tree turtles and providing examples of tree turtle implementations. Tree turtles can also be extended to be made Byzantine fault-tolerant (BFT). The modularity of tree turtles allows a generic approach for adding a leader for liveness. We expect that these abstractions will simplify reasoning and formal verification of SMR protocols as well as facilitate innovation in protocol designs.
Security protocols enable secure communication over insecure channels. Privacy protocols enable private interactions over secure channels. Security protocols set up secure channels using cryptographic primitives. Privacy protocols set up private channels using secure channels. But just like some security protocols can be broken without breaking the underlying cryptography, some privacy protocols can be broken without breaking the underlying security. Such privacy attacks have been used to leverage e-commerce against targeted advertising from the outset; but their depth and scope became apparent only with the overwhelming advent of influence campaigns in politics. The blurred boundaries between privacy protocols and privacy attacks present a new challenge for protocol analysis. Covert channels turn out to be concealed not only below overt channels, but also above: subversions, and the level-below attacks are supplemented by sublimations and the level-above attacks.
Differential privacy (DP) is widely employed to provide privacy protection for individuals by limiting information leakage from the aggregated data. Two well-known models of DP are the central model and the local model. The former requires a trustworthy server for data aggregation, while the latter requires individuals to add noise, significantly decreasing the utility of aggregated results. Recently, many studies have proposed to achieve DP with Secure Multi-party Computation (MPC) in distributed settings, namely, the distributed model, which has utility comparable to central model while, under specific security assumptions, preventing parties from obtaining others' information. One challenge of realizing DP in distributed model is efficiently sampling noise with MPC. Although many secure sampling methods have been proposed, they have different security assumptions and isolated theoretical analyses. There is a lack of experimental evaluations to measure and compare their performances. We fill this gap by benchmarking existing sampling protocols in MPC and performing comprehensive measurements of their efficiency. First, we present a taxonomy of the underlying techniques of these s
While the existing literature on Differential Privacy (DP) auditing predominantly focuses on the centralized model (e.g., in auditing the DP-SGD algorithm), we advocate for extending this approach to audit Local DP (LDP). To achieve this, we introduce the LDP-Auditor framework for empirically estimating the privacy loss of locally differentially private mechanisms. This approach leverages recent advances in designing privacy attacks against LDP frequency estimation protocols. More precisely, through the analysis of numerous state-of-the-art LDP protocols, we extensively explore the factors influencing the privacy audit, such as the impact of different encoding and perturbation functions. Additionally, we investigate the influence of the domain size and the theoretical privacy loss parameters $ε$ and $δ$ on local privacy estimation. In-depth case studies are also conducted to explore specific aspects of LDP auditing, including distinguishability attacks on LDP protocols for longitudinal studies and multidimensional data. Finally, we present a notable achievement of our LDP-Auditor framework, which is the discovery of a bug in a state-of-the-art LDP Python package. Overall, our LDP-A
Protocols provide the unifying glue in concurrent and distributed software today; verifying that message-passing programs conform to such governing protocols is important but difficult. Static approaches based on multiparty session types (MPST) use protocols as types to avoid protocol violations and deadlocks in programs. An elusive problem for MPST is to ensure both protocol conformance and deadlock freedom for implementations with interleaved and delegated protocols. We propose a decentralized analysis of multiparty protocols, specified as global types and implemented as interacting processes in an asynchronous $π$-calculus. Our solution rests upon two novel notions: router processes and relative types. While router processes use the global type to enable the composition of participant implementations in arbitrary process networks, relative types extract from the global type the intended interactions and dependencies between pairs of participants. In our analysis, processes are typed using APCP, a type system that ensures protocol conformance and deadlock freedom with respect to binary protocols, developed in prior work. Our decentralized, router-based analysis enables the sound