The field of quantitative information flow (QIF) is concerned with measuring and controlling information leakage in computational systems, aiming to assess and improve their security. Much effort has been put into developing a mathematical framework for QIF, the standard approach being to model systems as monolithic infomation theoretic channels. However, many real-life systems can be best described by a collection of interacting channels instead. This motivates us to investigate the behaviour of channel compositions under the QIF framework. The channel compositions we study capture typical ways in which parts interact in real-world systems. Among other results, we derive relations between the information leakage of compositions and that of their components, establish whether we may substitute a component with a safer one without compromising the security of the whole, and model two anonymity protocols from the literature: the Dining Cryptographers and the Crowds.
The field of quantitative information flow (QIF) is concerned with measuring and controlling information leakage in computational systems, aiming to assess and improve their security. Much effort has been put into developing a mathematical framework for QIF, the standard approach being to model systems as monolithic infomation theoretic channels. However, many real-life systems can be best described by a collection of interacting channels instead. This motivates us to investigate the behaviour of channel compositions under the QIF framework. The channel compositions we study capture typical ways in which parts interact in real-world systems. Among other results, we derive relations between the information leakage of compositions and that of their components, establish whether we may substitute a component with a safer one without compromising the security of the whole, and model two anonymity protocols from the literature: the Dining Cryptographers and the Crowds.
The field of Quantitative Information Flow (QIF) is concerned with quantifying information leakage in systems. This work generalises the QIF framework to the quantum setting, having as foundations the recently developed g-leakage framework. Next, some recent results of the field of quantum statistical decision are presented and translated in terms of the "quantum" g-leakage framework, including a recently developed quantum generalisation of the Coriasceous Theorem, an important result for QIF.
Information flow is the branch of security that studies the leakage of information due to correlation between secrets and observables. Since in general such correlation cannot be avoided completely, it is important to quantify the leakage. The most followed approaches to defining appropriate measures are those based on information theory. In particular, one of the most successful approaches is the recently proposed g-leakage framework, which encompasses most of the information-theoretic ones. A problem with g-leakage, however, is that it is defined in terms of a minimization problem, which, in the case of large systems, can be computationally rather heavy. In this paper we study the case in which the channel associated to the system can be decomposed into simpler channels, which typically happens when the observables consist of multiple components. Our main contribution is the derivation of bounds on the (multiplicative version of) g-leakage of the whole system in terms of the g-leakages of its components. We also consider the particular cases of min-entropy leakage and of parallel channels, generalizing and systematizing results from the literature. We demonstrate the effectiveness of our method and evaluate the precision of our bounds using examples.
The thesis investigates a broad area of cryptography dealing with anonymity. We proposed a semi-formal model of anonymous channels (protocols for anonymous communication). Our model is able to capture many aspects of wide range of types of anonymous communication, however, we concentrate mostly on sender anonymity, receiver anonymity and relationship anonymity. These are the most basic types of anonymity and many others can be either derived from them or only slight modifications are required to include them into our model. Our model is based on protocol graphs (graphs describing communication patterns). Security properties are based on comparing these protocol graphs. If certain properties hold we can speak about anonymity achieved by a protocol. Our model also includes a novel idea of friends - participants who are allowed to know identity of some anonymous participant. Several anonymous channels together with their dining cryptographers based protocols are also presented in the thesis. These include protocols for the most basic anonymous channels (these are private bipartite channels) as well as for several complex channels. We also present information-theoretically secure protocols that make use of quantum resources. We were able to build a quantum protocol for an anonymous channel for which no classical protocol is known to exist (in the same cryptographic settings). Based on these anonymous channels and their protocols we also scratched surface of resource based reduction between cryptographic protocols. Because of complexity of all the areas of our research the thesis is written in semi-formal language. The main reason is flexibility and feasibility of working with the model. We use the well known language that is often used in IT security.
Today, hybrid cryptosystems are important part in structure of information telecommunication systems. That's why information security measures are extremely crucial at each stage of cryptosystem development life cycle. One of the most important specific of modern cryptosystems is the fact, that they often deployed in unprotected environment and outside the physically secured perimeter. That introduces new attack vectors, e.g. kleptographic attacks which include implementation forgery at endpoints. Such attack types are extremely dangerous because of the victim, who is a participant of some restricted area (electronic document flow, payment system, secure communication etc.), may induce threats for non-compromised participants (e.g., sensitive information leakage). One of the ways to solve mitigate this risks is development subliminal channel free cryptosystems which are resistant against different types of kleptographic attacks. In the article we show results belong to development of SETUP free cryptographic protocol development. Firstly, we suggest formal model for basic ''challenge-response'' protocol with subliminal channel. Using this formal model, we introduce sufficient conditions which lead to impossibility of existence of subliminal channels. Also the theorem about sufficient conditions has been formulated and proved. Further, we suggest improvements of basic protocols -- nonce generation and 1-round Diffie-Hellman key agreement protocol with design that is based of sufficient conditions. Using formalization of suggested enhanced protocols we formulated and proved the theorem about SETUP resistance property for these protocols. Our results may be useful for other SETUP free protocols development, this will be helpful for increasing security of hybrid cryptosystem.
We give diagrammatic tools to reason about information flow within encrypted communication. In particular, we are interested in deducing where information flow (communication or otherwise) has taken place, and fully accounting for all possible paths. The core mathematical concept is using a single categorical diagram to model the underlying mathematics, the epistemic knowledge of the participants, and (implicitly) the potential or actual communication between participants. A key part of this is a `correctness' or `consistency' criterion that ensures we accurately & fully account for the distinct routes by which information may come to be known (i.e. communication and / or calculation). We demonstrate how this formalism may be applied to answer questions about communication scenarios where we have the partial information about the participants and their interactions. Similarly, we show how to analyse the consequences of changes to protocols or communications, and to enumerate the distinct orders in which events may have occurred. We use various forms of Diffie-Hellman key exchange as an illustration of these techniques. However, they are entirely general; we illustrate in an appendix how other protocols from non-commutative cryptography may be analysed in the same manner.
Abstract: This study proposes a Post-Quantum Authenticated Key Exchange (PQ-AKE) framework designed to ensure cryptographic resilience in the presence of real-time side-channel leakage. The conceptual foundation integrates quantum-resistant primitives with adaptive leakage-aware control mechanisms, constructing a novel model that dynamically mitigates information exposure during key negotiation. The research framework builds upon existing post-quantum cryptographic architectures by embedding continuous telemetry to monitor side-channel emissions, enabling automated adaptation through a real-time feedback loop. Methodologically, the proposed protocol is formalized using game-based security proofs and experimentally validated through simulated adversarial models to evaluate key compromise probability, adaptive latency, and secrecy accuracy. The results reveal a significant reduction in key compromise probability and a marked improvement in adaptive response time compared to static leakage-resistant frameworks. This indicates the feasibility of integrating real-time resilience into quantum-safe protocols without sacrificing performance. The findings underscore the study’s broader implication: establishing self-regulating cryptographic ecosystems that can autonomously respond to leakage vectors, thereby setting a foundation for next-generation secure communication frameworks in hybrid and post-quantum infrastructures. Keywords Post-Quantum Cryptography, Authenticated Key Exchange, Side-Channel Leakage Resilience, Real-Time Adaptive Security, Quantum-Safe Communication Protocols, Leakage-Aware Cryptographic Frameworks, Adaptive Key Management, Cryptographic Telemetry, Hybrid Quantum-Classical Security, Secure Protocol Design