Hugo Santos Pereira

Hugo Santos Pereira

PhD Student @ NOVA LINCS

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publications

Automatic Generation of Contracts for Concurrent Java Programs

Published in INForum, 2022

Abstract: It is not uncommon for larger concurrent programs to have hundreds of atomic blocks and/or locks. As these programs become more and more complex, they become increasingly more prone to contain concurrency errors, as a programmer cannot easily take into account every possible interleaving. One way to address this problem is to analyse a concurrent program and generate a Contract for Concurrency, which identify the sequences of statements that must be executed atomically in a concurrent program. This method can be used either as documentation, for aiding development, or by an automatic tool to verify atomicity violations. Gluon is a static analysis tool that verifies such contracts for Java programs. Manually generating contracts for a large-scale codebase is unfeasible, and Gluon lightens this burden by providing an automated but rudimentary contract generation functionality. In this paper we propose a set of heuristics for automatically generating Contracts for Concurrency, and evaluate their accuracy with Gluon. With this new contract generation heuristics, we were able to fine-tune the contract generation, considerably reducing the number of spurious (unnecessary) clauses, which consequently reduced the analysis run time.

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MIRACE: Multipath Integrated Routing Architecture for Censorship Evasion

Published in NOVA School of Science and Technology (NOVA University Lisbon), 2025

Abstract: Contemporary research has underscored the alarming surveillance and censorship practices of totalitarian regimes and government agencies in observing traffic in communication networks, including the Internet. In response to these pressing challenges, anonymization networks have gained prominence in the digital landscape. Among these, Tor stands out as one of the most popular solutions, playing an essential role in protecting user privacy and anonymity, combating online censorship, and upholding the fundamental rights of free expression and communications. However, recent studies have uncovered vulnerabilities in the Tor network, including risks of deanonymization, often exploited with fingerprinting or correlation attacks launched by state-level adversaries or through the collaboration of multiple ones.
In this dissertation, we examine the issues of anonymity and privacy breaches within anonymization networks. To address these concerns, we present MIRACE - a multipath integrated routing architecture for a communication system that enhances privacy through mixed circuits, making communications resilient to tracing, blocking, and thus censorship. MIRACE mixed circuits are established through covert channels layered upon TLS, QUIC tunnels and WebRTC media streams, with different segments of a single circuit potentially using distinct covert methods. Our architecture allows traffic to be split across N circuits composed of M nodes, and each node incorporates advanced techniques like traffic encapsulation, shaping, and induced jitter. To the extent of our knowledge, our solution emerges as a pioneering contribution by combining per-packet traffic splitting with multi-protocol encapsulation, and it aims at bolstering the defences against state-of-the-art Internet censorship mechanisms. Moreover, the techniques addressed in this proposal are also potential candidates for future enhancements of Tor.
We have implemented a prototype and performed extensive validations to observe the correctness and experimental performance of MIRACE. The obtained results show that the proposed solution operates as expected with throughput on the order of Mbps and maintains latency conditions suitable for diverse application contexts and usage scenarios. Furthermore, the proposed system is also resistant to unobservability evaluations regarding website fingerprinting.

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Traffic Shaping for Network Protocols: A Modular and Developer-Friendly Framework

Published in Free and Open Communications on the Internet, 2025

Abstract: Censorship-resistant systems and privacy-preserving communication tools are increasingly vulnerable to detection by adversaries using deep packet inspection (DPI) and traffic analysis. While encryption ensures the confidentiality of packet payloads, metadata, such as packet sizes, burst patterns, and timing characteristics, remain exposed and can be exploited to fingerprint and block these tools or deanonymize their endpoints. Both historical evidence of real-world censorship techniques and research-based approaches have demonstrated the vulnerability of these systems to attacks that exploit packet metadata. However, in many of these examples, we observe that typically, the initial seconds of communication between the user and the system’s proxy are sufficient to carry out the attacks. In this work, we present the design of a modular framework for shaping the initial seconds of a user-proxy connection aimed at mitigating the above-described vulnerabilities with minimal performance overhead. Central to our framework are two components: a scheduler, which intercepts and shapes packets exchanged between the user and the system’s proxy, and a shaper policy, which defines how the scheduler shapes the exchanged traffic. We plan to base our shaping policies on two main approaches: (1) predefined or user-configurable schedules and (2) traffic patterns generated by a generative adversarial network (GAN) designed to mimic realistic behavior. By targeting the initial communication phase, where many classifiers extract highly discriminative features, we hypothesize that we can provide robust protection against DPI and traffic analysis attacks that threaten real-world systems designed to evade censorship or provide user privacy.

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Privocracy: Online Democracy through Private Voting

Published in arXiv preprint (arXiv:2602.01341), 2026

Abstract: In traditional access control policies, every access granted and administrative account introduces an additional vulnerability, as a corruption of a high-privilege user can compromise several sensitive files. Privocracy is an access control mechanism that minimizes the need to attribute high privileges by triggering a secure e-voting procedure to run commands that require using sensitive resources. With Privocracy an organization can distribute trust in resource access, minimizing the system vulnerabilities from single points of failure, all while maintaining the high flexibility of discretionary access control policies. The Privocracy voting mechanism achieves everlasting privacy, ensuring votes remain confidential regardless of an adversary’s computational power, while addressing the dependability requirements of a practical and secure system. The procedure incorporates useful features such as vote delegation to reduce voter fatigue, rapid voting rounds to enable quick action during emergencies, and selective vote auditing for application-level accountability. Our experimental results demonstrate that Privocracy processes votes efficiently and can be deployed on commodity hardware.

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