News January 2019. Throughout 2019, we are setting up an Interdisciplinary Master Program in Space Resources. This is an opportunity to revisit and improve methods for reliable systems engineering. It is also an opportunity to explore security demands in the face of increased cooperation and competition for space.
Jobs advertised: postdoctoral positions are available. Please consider applying!
I summarise key results and research directions.
Equivalence checking and privacy. In my previous post as senior research fellow at Nanyang Technological University, Singapore, we solved several problems in protocol verification which use logic to give us a better understanding of congruences for process calculi [CONCUR'17,LICS'18]. These breakthroughs enable us to define, what I argue is, an optimal technique for verifying privacy properties using cryptographic calculi. A future challenge is to build the technique into tools used to verify cryptographic protocols.
Linked Data. My PhD thesis at University of Southampton was on high-level languages for consuming data published on the Web. Such language abstractions [Sci.Comp.Prog.'14,JLAMP'15,JLAMP'16] allow programs to engage in sessions, where information discovered in queries can be used to form new queries, thereby navigating an interlinked Web of Data. Providing high-level language abstractions makes such programming tasks easier. This led me to the notion of a descriptive type system, which assists the data consumer during such interactions by generating suggestions for how inconsistencies in data may be resolved.
On session types and proof theory. I believe my paper providing a proof theoretic approach to multi-party session type system Scribble [PSI'15,Sci.Ann.Comp.Sci.'15] presents significant insights for both the session type and proof theory communities. This work perhaps challenges the culture of type theorists, who, at times, equate proof theory for types with the Curry-Howard correspondence. While the Curry-Howard correspondence is a remarkable achievement; my message to the session type community is that proof theory has much more to offer other than the Curry-Howard isomorphism, as demonstrated by this work.
Attack trees. Attack trees, employed for security assessment, are also amenable to proof theoretic techniques [Fund.Inf.'16, GramSec'18]. This is natural, since there is a game theoretic explanation of the logical system I use, which naturally accounts for tensions between an attacker and defender competing on an attack surface.
September 2017: A paper on modal logics for processes was awarded best paper at CONCUR 2017. See the press release for the award. The paper concerns a process equivalence called open bisimilarity which is easily automated and has desirable algebraic properties. Open bisimilarity treats input values in a call-by-need fashion. For example, if you receive a notification that an e-mail has arrived, there is no need to immediately check the email; you can continue working and later read the email when you need a detail contained within. The surprising insight of our paper is that there is a fundamentally intuitionistic logical characterisation of open bisimilarity (due to the call-by-need treatment of inputs inducing ``intuitionistic hereditary'').
An extended journal verion is under review.
Ki Yung Ahn, Ross Horne and Alwen Tiu. A Characterisation of Open Bisimilarity using an Intuitionistic Modal Logic. 28th International Conference on Concurrency Theory (CONCUR 2017). Editors: Roland Meyer and Uwe Nestmann; Volume 85; Article No. 7; pp. 7:1-7:17. Leibniz International Proceedings in Informatics. DOI:10.4230/LIPIcs.CONCUR.2017.7
March 2018: A paper on mismatch has been accepted at LICS 2018. The paper explains why mismatch (the else branch in a statement such as "if M = N then P else Q") should be treated intuitionistically when reasoning about processes compositionally. In particular, we introduce the coarsest bisimilarity congruence for processes with if-then-else branching. The logical characterisation of this congruence is also intuitionistic, treating public information intuitionistically but private information classically. We highlight that this congruence and logic have impact in the area of verifying privacy protocols, where "else" branches avoid inadvertent leaks by providing dummy data.
Ross Horne, Ki Yung Ahn, Shang-wei Lin and Alwen Tiu. Quasi-Open Bisimilarity with Mismatch is Intuitionistic. In Proceedings of LICS '18: 33rd Annual ACM/IEEE Symposium on Logic in Computer Science, Oxford, United Kingdom, July 9-12, 2018 (LICS '18). 10 pages. DOI:10.1145/3209108.3209125
A technical report explains how the techniques lift to the full applied π-calculus. Lifting to the applied π-calculus, makes it possible to verify privacy properties of real-world cryptographic protocols.
March 2017: A paper on causal attack trees has been published in Fundamenta Informaticae. Causal attack trees profile the sub-goals of the proponent of an attack, by refining goals disjunctively, conjunctively and sequentially. We provide the machinery for determining whether one attack specialises another attack. Specialisation preserves correlations between answers to quantitative questions concerning attacks such as the "minimum attack time".
Ross Horne, Sjouke Mauw and Alwen Tiu. Semantics for Specialising Attack Trees based on Linear Logic. Fundamenta Informaticae 153(1-2). pp. 57-86. IOS Press. DOI:10.3233/FI-2017-1531
A supporting technical report includes proofs omitted from the journal version.
The game semantics behind such attack trees is explored in a paper presented at GraMSec'18. We emphasise the difference between when an attacker making a choice and when the environment or defender makes a choice in an attack scenario.
Ross Horne, Sjouke Mauw and Alwen Tiu. The Attacker Does not Always Hold the Initiative: Attack Trees with External Refinement. In proceedings G. Cybenko et al. (Eds.): The Fifth International Workshop on Graphical Models for Security Oxford (GraMSec 2018), UK - July 8, 2018. Lecture Notes in Computer Science 11086, pp. 90–110, Springer. 2019 DOI:10.1007/978-3-030-15465-3_6
June 2016: The following paper on logical systems for process calculi is published in the proceedings of CONCUR 2016. The paper introduces a new logical system, directly embedding various process calculi, not limited to Robin Milner's famous π-calculus. The trick is, to capture private names, we decompose established self-dual nominal quantifiers into a De Morgan dual pair of nominal quantifiers. Following the tradition of Gabbay and Pitts, we use Cyrillic vowels И and Э, pronounced `new' and `wen' respectively, for our pair of nominal quantifiers. The logical system opens doors for reasoning about processes, particularly for soundly reasoning about processes deployed on scalable high-availability distributed systems.
Ross Horne, Alwen Tiu, Bogdan Aman and Gabriel Ciobanu. Private Names in Non-Commutative Logic. 27th International Conference on Concurrency Theory (CONCUR 2016). Editors: Josée Desharnais and Radha Jagadeesan; Article No. 31; pp. 31:1-31:16. Leibniz International Proceedings in Informatics. DOI:10.4230/LIPIcs.CONCUR.2016.31
A technical report submitted to a journal contains the details of the cut elimination proof.
March 2019. This processes-as-formulae research agenda is summarised in the following paper in the journal Mathematical Structures in Computer Science. The paper develops novel technique allowing us to prove that, as notion of refinement for processes, linear implication is strictly finer than weak simulation preorders. The technique lifts to a range of process calculi, not only the π-calculus. This is the tightest and most expressive result of its kind in the literature.
Ross Horne and Alwen Tiu. Constructing Weak Simulations from Linear Implications for Processes with Private Names. Mathematical Structures in Computer Science. pages 1-34 (volume to be assigned). Cambridge University Press (2019). DOI:10.1017/S0960129518000452
December 2015: Two papers are published on session types employing techniques from proof theory:
Ross Horne. The consistency and complexity of multiplicative additive system virtual. Scientific Annals of Computer Science, 25.2(2015): 245-316. DOI:10.7561/SACS.2015.2.245
This paper presents a consistent logical system where series-parallel composition and choice coexist happily.
Gabriel Ciobanu and Ross Horne. Behavioural analysis of sessions using the calculus of structures. In Perspectives of System Informatics, 10th International Andrei Ershov Informatics Conference, PSI 2015, in Memory of Helmut Veith, Kazan and Innopolis, Russia, August 24-27, 2015. Editors: Mazzara, Manuel, Voronkov, Andrei. LNCS 9609, pages 91-106, Springer (2015). DOI:10.1007/978-3-319-41579-6_8
This paper presents a semantics for finite session types based on the above logical system. The semantics logically characterises multi-party compatibility and subtyping. This work is a tight match for the practical session modelling language Scribble.
February 2016: The second of two journal papers on RDF Schema from the perspective of type systems is published in Journal of Logical and Algebraic Methods in Programming. These two papers represent a mature line of work that is ready to be implemented by a graduate student interested in making data on the Web easier to consume.
Gabriel Ciobanu, Ross Horne, and Vladimiro Sassone. Minimal type inference for Linked Data consumers. Journal of Logical and Algebraic Methods in Programming 84.4 (2015): 485-504. DOI:10.1016/j.jlamp.2014.12.005
Gabriel Ciobanu, Ross Horne, and Vladimiro Sassone. A descriptive type foundation for RDF Schema. Journal of Logical and Algebraic Methods in Programming 85.5 (2016): 681-706. DOI:10.1016/j.jlamp.2016.02.006
The first of the two papers provides a gentle introduction to consuming data on the Web called Linked Data and introduces a simple scripting language, with a conventional "prescriptive" type system, that makes the consumer's life easier.
The second of the two papers addresses more challenging aspects of RDF Schema types. The paper introduces a novel "descriptive" type system that evolves to describe data discovered at run-time by the Linked Data consumer. The descriptive type system can adapt to several modes of inference ranging from W3C standard compliant RDF Schema inference to something more accommodating. When the descriptive type system is unsure about the appropriate mode of inference, a warning with a menu of options is generated for the consumer reflecting the subjective nature of knowledge published on the Web.
The slides are available.
Before joining the "Security and Trust of Software Systems" group at University of Luxembourg, I was a senior research fellow in the Cyber Security Lab at Nanyang Technological University Singapore. There I was driving a project, lead by Ass.Prof. Alwen Tiu, that advanced the state of the art for symbolic analysis of security protocols. I also had the pleasure to contribute to projects under Ass.Prof. Shang-Wei Lin and Assoc.Prof. Liu Yang.
The proceedings of the workshop Embracing Global Computing in Emerging Economies (EGC2015) represents my effort to galvanise grass roots computer science research in Almaty and across the region.
Almaty, the cosmopolitan hub of Central Asia, is a magical city for winter sports, the steppe in spring, the mountains in summer and fruits of autumn.
I defended my PhD in computer science, with a thesis titled Programming Languages and Principles for Read-Write Linked Data, in 2011 under the supervision of Prof Vladimiro Sassone at University of Southampton, UK. My BA in Mathematics and Computer Science, with first class honours and a thesis titled Computable Cyclic Functions, was awarded by Oxford University, UK, in 2005.
I have had the honour and pleasure to collaborate with Sjouke Mauw, Alwen Tiu, Gabriel Ciobanu, Vladimiro Sassone, Mariangiola Dezani-Ciancaglini, Bogdan Aman, Shang-wei Lin, Barbara Kordy, Paola Giannini, Ilaria Castellani, Nicholas Gibbins, Cristian Văideanu, and Ki Yung Ahn. I look forward to future collaborations.
I am a European. I believe passionately that our doors should be open to everyone.