2021
Authors
Almeida, JB; Barbosa, M; Correia, ML; Eldefrawy, K; Graham-Lengrand, S; Pacheco, H; Pereira, V;
Publication
CCS '21: PROCEEDINGS OF THE 2021 ACM SIGSAC CONFERENCE ON COMPUTER AND COMMUNICATIONS SECURITY
Abstract
MPC-in-the-Head (MitH) is a general framework that enables constructing efficient zero-knowledge (ZK) protocols for NP relations from secure multiparty computation (MPC) protocols. In this paper we present the first machine-checked implementations of MitH. We begin with an EasyCrypt formalization that preserves the modular structure of the original construction and can be instantiated with arbitrary MPC protocols, and secret sharing and commitment schemes satisfying standard notions of security. We then formalize various suitable components, which we use to obtain full-fledged ZK protocols for general relations. We compare two approaches for obtaining verified executable implementations. The first uses a fully automated extraction from EasyCrypt to OCaml. The second reduces the trusted computing base (TCB) and provides better performance by combining code extraction with formally verified manual low-level components implemented in the Jasmin language. We conclude with a discussion of the trade-off between the formal verification effort and the performance of resulting executables, and how our approach opens the way for fully verified implementations of state-of the-art optimized protocols based on MitH.
2022
Authors
Almeida, JCB; Barbosa, M; Barthe, G; Pacheco, H; Pereira, V; Portela, B;
Publication
JOURNAL OF LOGICAL AND ALGEBRAIC METHODS IN PROGRAMMING
Abstract
Secure multiparty computation (SMC) allows for complex computations over encrypted data. Privacy concerns for cloud applications makes this a highly desired technology and recent performance improvements show that it is practical. To make SMC accessible to non-experts and empower its use in varied applications, many domain-specific compilers are being proposed.We review the role of these compilers and provide a formal treatment of the core steps that they perform to bridge the abstraction gap between high-level ideal specifications and efficient SMC protocols. Our abstract framework bridges this secure compilation problem across two dimensions: 1) language-based source- to target-level semantic and efficiency gaps, and 2) cryptographic ideal- to real-world security gaps. We link the former to the setting of certified compilation, paving the way to leverage long-run efforts such as CompCert in future SMC compilers. Security is framed in the standard cryptographic sense. Our results are supported by a machine-checked formalisation carried out in EasyCrypt.
2021
Authors
Pacheco, H; Macedo, N;
Publication
International Journal of Robotic Computing
Abstract
2023
Authors
Portela, B; Pacheco, H; Jorge, P; Pontes, R;
Publication
2023 IEEE 36TH COMPUTER SECURITY FOUNDATIONS SYMPOSIUM, CSF
Abstract
Conflict-free Replicated Data Types (CRDTs) are a very popular class of distributed data structures that strike a compromise between strong and eventual consistency. Ensuring the protection of data stored within a CRDT, however, cannot be done trivially using standard encryption techniques, as secure CRDT protocols would require replica-side computation. This paper proposes an approach to lift general-purpose implementations of CRDTs to secure variants using secure multiparty computation (MPC). Each replica within the system is realized by a group of MPC parties that compute its functionality. Our results include: i) an extension of current formal models used for reasoning over the security of CRDT solutions to the MPC setting; ii) a MPC language and type system to enable the construction of secure versions of CRDTs and; iii) a proof of security that relates the security of CRDT constructions designed under said semantics to the underlying MPC library. We provide an open-source system implementation with an extensive evaluation, which compares different designs with their baseline throughput and latency.
2012
Authors
Pacheco, H; Cunha, A; Hu, Z;
Publication
ECEASST
Abstract
Existing bidirectional languages are either state-based or operation-based, depending on whether they represent updates as mere states or as sequences of edit operations. In-between both worlds are delta-based frameworks, where updates are represented using alignment relationships between states. In this paper, we formalize delta lenses over inductive types using dependent type theory and develop a point-free delta lens language with an explicit separation of shape and data. In contrast with the already known issue of data alignment, we identify the new problem of shape alignment and solve it by lifting standard recursion patterns such as folds and unfolds to delta lenses that use alignment to infer meaningful shape updates. © Bidirectional Transformations 2012.
2012
Authors
Macedo, N; Pacheco, H; Cunha, A;
Publication
Relational and Algebraic Methods in Computer Science - 13th International Conference, RAMiCS 2012, Cambridge, UK, September 17-20, 2012. Proceedings
Abstract
The calculus of relations has been widely used in program specification and reasoning. It is very tempting to use such specifications as running prototypes of the desired program, but, even considering finite domains, the inherent partiality and non-determinism of relations makes this impractical and highly inefficient. To tame partiality we prescribe the usage of invariants, represented by coreflexives, to characterize the exact domains and codomains of relational specifications. Such invariants can be used as pre-condition checkers to avoid runtime errors. Moreover, we show how such invariants can be used to narrow the non-deterministic execution of relational specifications, making it viable for a relevant class of problems. In particular, we show how the proposed techniques can be applied to execute specifications of bidirectional transformations, a domain where partiality and non-determinism are paramount. © 2012 Springer-Verlag.
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