research

TL;DR: I work or have worked on

• Formal methods for Concurrent and Distributed Systems
  • process calculi (CCS, π-calculus, et similia)
  • bigraphs and bigraphic reactive systems
  • models and languages for IoT, CAS and edge computing
  • modelisation and verification of security protocols
  • quantitative systems (DMC, CTMC, MDP)
• Distributed architectures, languages and security
  • cooperating communicating processes
  • peer-to-peer, pub-sub and event-based architectures
  • distributed ledgers
  • security of virtualization and containerization
  • information flow control
• Logic and Category theory
  • Modal, temporal and spatial logics
  • Monads, algebras, coalgebras
  • Fuzzy and nominal sets
• Type theory
  • session and behavioural types
  • logical frameworks
  • proof assistants (Coq, Agda,…)

Research statement

My research mission revolves around the fundamental enhancement of concurrent and distributed systems — making them not only more effective and robust but also inherently secure. It’s a multi-faceted approach that amalgamates formal methods, advanced programming language techniques, logic, category theory, and the foundational principles of computer security. This interdisciplinary foundation is pivotal to tackle the intricate challenges inherent in concurrent systems, providing a solid theoretical framework to enhance both their functionality and security.

Within this framework, my objectives are two-fold. First, I aim to elevate system reliability and security by addressing critical aspects such as synchronization issues and potential vulnerabilities. These are the linchpins of robust and secure concurrent systems. Second, I strive to contribute to a broader understanding of computational processes, especially in the context of secure concurrent systems. This comprehension is essential for driving innovation and ensuring that our systems can withstand the ever-evolving landscape of cyber threats.

Ultimately, my goal is to foster innovation, pushing the boundaries of distributed programming, analysis, and security methodologies. By blending the power of formal methods, advanced programming techniques, and a solid mathematical and security-driven foundation, I aspire to not only enhance concurrent systems but also pave the way for a safer and more efficient digital future.

Research history

My research career has been dedicated to developing formal methods for modeling, verification, and analysis of complex systems, ensuring their trustworthiness. Along over three decades and almost one hundred papers, my interests have evolved within this broad landscape, tackling new challenges as they emerged. Here I recall the main achievements; see publications for the complete list of papers.

My initial work (1994-1997 and 2000-2006) centered on formalizing programs and processes within logical frameworks and proof assistants based on type theory (e.g., Lego, Coq). Recognizing the theoretical and practical limitations of existing tools, I concentrated on developing novel techniques to streamline the formalization and reasoning process. A key outcome of this effort was the introduction of the weak Higher-Order Abstract Syntax (weak HOAS) technique for handling binders in inductive type theories (Honsell & Miculan, 1995)(Miculan, 1997)(Miculan, 1999). This innovation, now a standard technique within the Coq community, continues to be actively used for reasoning about languages with binders.
While powerful, weak HOAS presents challenges for reasoning by induction over higher-order terms. To address this, we introduced the Theory of Contexts, a set of three axioms that demonstrably improve inductive reasoning (Honsell et al., 2001); this work is still a landmark in formal reasoning about π-calculus and similar models in Coq. However, adding axioms to a complex system like Coq requires careful consideration. We formally proved the soundness of the Theory of Contexts using category-theoretic constructions called tripos (Bucalo et al., 2006). This work, in collaboration with the late Martin Hofmann, marked my second significant encounter with category theory, which became a cornerstone of my subsequent research.
As a side note, the introduction of (weak) HOAS sparked significant interest in the research community around higher-order abstract syntax and binders, yielding three influential papers at LICS 1999 (Fiore et al., 1999; Hofmann, 1999; Gabbay and Pitts, 1999). In particular, the latter laid the foundation for the new and thriving area of theoretical computer science called “nominal techniques”. We have investigated the connections between these approaches to binders in (Miculan & Yemane, 2005)(Gadducci et al., 2006).

Another limitation of type theory-based logical frameworks is that circular definitions are subject to syntactic restrictions to ensure their termination and productivity. These restrictions decrease the expressive power of the language. To address this problem, we have proposed a very general Banach-like theorem for defining fixed-points in categories of sheaves (Di Gianantonio & Miculan, 2004). This result gives a unifying and general account of most techniques used in computer science in order to ensure convergency of circular definitions, such as well-founded recursion and contractivity in complete ultrametric spaces. Furthermore, to achieve a more natural and practical approach, we introduced the notion of complete ordered families of equivalence relations (COFE) in (Di Gianantonio & Miculan, 2003). COFE offer a more intuitive alternative to specific ultrametric spaces and integrates well with formalizations. This led to COFE becoming a standard tool in synthetic guarded domain theory and step-indexed logical relations like in Iris, a verification framework crucial for proving the correctness and semantic soundness of the Rust programming language. Years later, this interesting subject re-emerged during a visit to Aarhus, resulting in a collaborative work with Lars Birkedal’s group (Bizjak et al., 2014).

My exploration of logical frameworks sparked an interest in metamodels, which became the main subject of my second research period (2006-2016). Metamodels are abstract frameworks that allow for proving general results about entire classes of models. Logical frameworks themselves can be viewed as logical metamodels, ideal for reasoning about logical systems. Other metamodels offer advantages for reasoning about the operational semantics of programs and processes. I particularly investigated Bigraphs and Bigraphical Reactive Systems (BRSs), a graphical metamodel conceived by Robin Milner. BRSs offer a powerful approach to describing the syntax and semantics of distributed systems by leveraging the distinct concepts of connectivity and locality. To address limitations in original bigraphs, we introduced directed bigraphs (Grohmann & Miculan, 2007). This extension enhanced expressivity while preserving the core strengths of bigraphs, particularly the RPO construction and bisimulations. Directed bigraphs proved valuable for modeling various systems, including Fusion calculus (previously incompatible with standard bigraphs) (Grohmann & Miculan, 2007), Access control systems (Grohmann & Miculan, 2008), Systems biology (Bacci et al., 2009)(Bacci et al., 2009), Multi-agent systems (Mansutti et al., 2014). Furthermore, I actively contributed to bigraph tooling. Our initial DBtk toolkit (Bacci et al., 2009) has been succeeded by jLibBig, a Java library for bigraphs and BRSs, which remains actively developed and used by the community; the core algorithms are described in (Chiapperini et al., 2020)(Chiapperini et al., 2022). In (Mansutti et al., 2015) we presented a fully decentralized implementation of bigraph matching, suited to distributed systems where the bigraph structure is distributed among various nodes, instead of being stored in a centralized server. Distributed matching can help to deal with the intrinsic complexity of bigraph matching, which is NP-complete as we proved in (Bacci et al., 2014).

My work on modelling Fusion calculus with bigraphs led me to investigate bialgebras, a unifying framework for operational and denotational semantics introduced by Turi and Plotkin. Previously (Miculan & Scagnetto, 2003), I extended this framework to typed higher-order abstract syntax and semantics using presheaf categories. With similar techniques, in (Miculan, 2008) I have given a bialgebraic semantics of Fusion calculus, fitting the notion of hyperbisimulation in the coalgebraic setting.
Inspired by applications in systems biology (Bacci & Miculan, 2010)(Bacci & Miculan, 2012), I became interested in using bialgebras and related GSOS rule formats to model quantitative aspects of systems. This resulted in the introduction of the first structural operational semantics for continuous state probabilistic processes (Bacci & Miculan, 2012) and a general GSOS for non-deterministic processes with quantitative features (Miculan & Peressotti, 2014).

Beyond standard bisimulation, I explored the concept of weak bisimulation, which considers unobservable actions. In (Miculan & Peressotti, 2013), we extended the coalgebraic framework to handle various system behaviors using weighted semirings. This approach unifies weak bisimulations for non-deterministic and fully probabilistic systems, and offers a definition for systems where it was previously lacking (e.g., stochastic systems). A comprehensive theory of behavioural equivalences for coalgebras with unobservable moves has been presented in (Brengos et al., 2015). Additionally, we developed a general algorithm (Miculan & Peressotti, 2017) for efficiently deciding weak bisimulations in a broad class of systems. And using categorical tools in (Bernardo & Miculan, 2016)(Bernardo & Miculan, 2019) we established an unexpected result: disjunctive probabilistic modal logic is enough to fully characterize bisimilarity on reactive probabilistic systems (also known as Markov decision processes).

The study of metamodels for distributed computational models increased my interest in security and trustworthiness issues of distributed, component-based, and smart systems, which is the focus of my third (and current) research period (2016-today). These systems involve intricate interactions of numerous heterogeneous components, making their behavior complex to analyze. To address this challenge, currently I leverage formal methods (with a pinch of machine learning) to develop novel models, languages, methodologies, and verification techniques to formally analyze and ensure the security and trustworthiness of these systems. I approach this subject from multiple angles, focusing on coordination and security issues.

First, we explored transactional memory models to improve coordination in distributed systems. We introduced an expressive Haskell-like language with open transactions (Miculan et al., 2015)(Miculan & Peressotti, 2016). This language allows processes to join transactions dynamically, overcoming limitations of traditional models in coordinating communicating processes. Along this line, we developed Acidify (Geatti et al., 2019), an abstract middleware for coordinating transactions between distributed processes accessing shared storage services, possibly in the cloud. Acidify supports heterogeneous storage, including both local and remote options. We implemented Acidify in Erlang and provided bindings for popular storage services like Riak KV and Amazon S3.

A key area of my current research involves formal models and tools for reasoning about composable microservice-oriented architectures based on container technologies, like Docker and Kubernetes. In (Burco et al., 2020) we introduced a formal model for these systems using the framework of Bigraphical Reactive Systems (BRSs). This model effectively captures various architectural aspects of containerized applications. For instance, the composition of containers directly translates to the composition of corresponding bigraphs within an “environment bigraph.” This foundational model has led to important developments and tools, such as DBCChecker (Altarui et al., 2023), a bigraph-based tool for verifying security properties of container compositions statically, i.e. before deploying the application. I’m actively expanding on this research within the SECCO and SWOPS projects of PNRR SERICS.

Still related to static analysis of composable systems is the work (Stolze et al., 2021)(Stolze et al., 2023), where we introduced a theory of composable partial multiparty session types for open systems. This novel approach allows composing partial sessions without requiring a predefined global type or complete knowledge of missing components. Partial session types capture the individual perspectives of participants, enabling the merging of compatible views during composition to form a unified session view. In cases of incompatibility (e.g., due to miscommunication or deadlocks), the merging phase detects these issues.

Security issues have always intrigued me, even during my earlier research in other areas. In (Maiero & Miculan, 2011) we developed one of the first methods for intrusion detection based on system call traces in paravirtualized systems (a la Xen); in (Miculan & Urban, 2011) we conducted the first formal analysis of Facebook Connect’s Single Sign-On protocol using AVISPA. In recent years, my work on formal analysis of security protocols has become more systematic. First, in (Mansutti & Miculan, 2018) we have proved the decidability of hedge bisimulation on finite processes of the applied π-calculus. Utilizing the ProVerif tool (which adopts the applied π-calculus for representing cryptographic protocols), we have investigated the security of Telegram’s MTProto 2.0 protocol (Miculan & Vitacolonna, 2021)(Miculan & Vitacolonna, 2023) and the Multi-Factor Authentication of Italian e-IDAS digital identity card CIE (Van Eeden et al., 2024)(Paier et al., 2024) (the latter work has received the Best Paper Award at SEFM 2024). This research line also connects with DBCChecker (Altarui et al., 2023), which leverages ProVerif as its backend verification engine.

Beyond microservices and containers, I’m actively exploring edge computing, an emerging paradigm where computations shift from the cloud to devices interacting with the environment. This approach enhances reliability, scalability, privacy, and security. However, effective communication and coordination among potentially large numbers of distributed edge components require suitable abstractions. To this end, we introduced AbU, a calculus for modeling and reasoning about Event-Condition-Action (ECA) systems with attribute-based communication (Miculan & Pasqua, 2021)(Pasqua & Miculan, 2023). This communication model facilitates coordination among large node families in a declarative manner. AbU is being implemented in Go and other languages (see tools for the AbU Language and (Pasqua et al., 2022)) and serves as the foundation for verifying security and safety properties of distributed IoT systems through static or dynamic analysis (Pasqua & Miculan, 2021)(Pasqua & Miculan, 2024)(Pasqua & Miculan, 2024).

While my focus has shifted towards distributed programming language theory and security protocol analysis, I remain committed to foundational research, particularly in graph-based metamodels. In recent work (Castelnovo et al., 2022)(Castelnovo et al., 2024), we introduced a novel criterion for 𝓜,𝓝-adhesivity, a crucial property for categories in algebraic rewriting. This new criterion finds application in hierarchical graph structures like bigraphs.

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