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Documents authored by Sánchez, César

Document
DOI: 10.4230/OASIcs.FMBC.2022.5
Multi: A Formal Playground for Multi-Smart Contract Interaction

Authors: Martín Ceresa and César Sánchez

Published in: OASIcs, Volume 105, 4th International Workshop on Formal Methods for Blockchains (FMBC 2022)

Abstract
Blockchains are maintained by a network of participants, miner nodes, that run algorithms designed to maintain collectively a distributed machine tolerant to Byzantine attacks. From the point of view of users, blockchains provide the illusion of centralized computers that perform trustable verifiable computations, where all computations are deterministic and the results cannot be manipulated or undone. Every blockchain is equipped with a crypto-currency. Programs running on blockchains are called smart-contracts and are written in a special-purpose programming language with deterministic semantics. Each transaction begins with an invocation from an external user to a smart contract. Smart contracts have local storage and can call other contracts, and more importantly, they store, send and receive cryptocurrency. Once installed in a blockchain, the code of the smart-contract cannot be modified. Therefore, it is very important to guarantee that contracts are correct before deployment. However, the resulting ecosystem makes it very difficult to reason about program correctness, since smart-contracts can be executed by malicious users or malicious smart-contracts can be designed to exploit other contracts that call them. Many attacks and bugs are caused by unexpected interactions between multiple contracts, the attacked contract and unknown code that performs the exploit. Moreover, there is a very aggressive competition between different blockchains to expand their user base. Ideas are implemented fast and blockchains compete to offer and adopt new features quickly. In this paper, we propose a formal playground that allows reasoning about multi-contract interactions and is extensible to incorporate new features, study their behaviour and ultimately prove properties before features are incorporated into the real blockchain. We implemented a model of computation that models the execution platform, abstracts the internal code of each individual contract and focuses on contract interactions. Even though our Coq implementation is still a work in progress, we show how many features, existing or proposed, can be used to reason about multi-contract interactions.
Cite as

Martín Ceresa and César Sánchez. Multi: A Formal Playground for Multi-Smart Contract Interaction. In 4th International Workshop on Formal Methods for Blockchains (FMBC 2022). Open Access Series in Informatics (OASIcs), Volume 105, pp. 5:1-5:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{ceresa_et_al:OASIcs.FMBC.2022.5,
  author =	{Ceresa, Mart{\'\i}n and S\'{a}nchez, C\'{e}sar},
  title =	{{Multi: A Formal Playground for Multi-Smart Contract Interaction}},
  booktitle =	{4th International Workshop on Formal Methods for Blockchains (FMBC 2022)},
  pages =	{5:1--5:16},
  series =	{Open Access Series in Informatics (OASIcs)},
  ISBN =	{978-3-95977-250-1},
  ISSN =	{2190-6807},
  year =	{2022},
  volume =	{105},
  editor =	{Dargaye, Zaynah and Schneidewind, Clara},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.FMBC.2022.5},
  URN =		{urn:nbn:de:0030-drops-171868},
  doi =		{10.4230/OASIcs.FMBC.2022.5},
  annote =	{Keywords: blockchain, formal methods, theorem prover, smart-contracts}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2022.27
Expressiveness and Decidability of Temporal Logics for Asynchronous Hyperproperties

Authors: Laura Bozzelli, Adriano Peron, and César Sánchez

Published in: LIPIcs, Volume 243, 33rd International Conference on Concurrency Theory (CONCUR 2022)

Abstract
Hyperproperties are properties of systems that relate different executions traces, with many applications from security to symmetry, consistency models of concurrency, etc. In recent years, different linear-time logics for specifying asynchronous hyperproperties have been investigated. Though model checking of these logics is undecidable, useful decidable fragments have been identified with applications e.g. for asynchronous security analysis. In this paper, we address expressiveness and decidability issues of temporal logics for asynchronous hyperproperties. We compare the expressiveness of these logics together with the extension S1S[E] of S1S with the equal-level predicate by obtaining an almost complete expressiveness picture. We also study the expressive power of these logics when interpreted on singleton sets of traces. We show that for two asynchronous extensions of HyperLTL, checking the existence of a singleton model is already undecidable, and for one of them, namely Context HyperLTL (HyperLTL_C), we establish a characterization of the singleton models in terms of the extension of standard FO[<] over traces with addition. This last result generalizes the well-known equivalence between FO[<] and LTL. Finally, we identify new boundaries on the decidability of model checking HyperLTL_C.
Cite as

Laura Bozzelli, Adriano Peron, and César Sánchez. Expressiveness and Decidability of Temporal Logics for Asynchronous Hyperproperties. In 33rd International Conference on Concurrency Theory (CONCUR 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 243, pp. 27:1-27:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bozzelli_et_al:LIPIcs.CONCUR.2022.27,
  author =	{Bozzelli, Laura and Peron, Adriano and S\'{a}nchez, C\'{e}sar},
  title =	{{Expressiveness and Decidability of Temporal Logics for Asynchronous Hyperproperties}},
  booktitle =	{33rd International Conference on Concurrency Theory (CONCUR 2022)},
  pages =	{27:1--27:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-246-4},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{243},
  editor =	{Klin, Bartek and Lasota, S{\l}awomir and Muscholl, Anca},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2022.27},
  URN =		{urn:nbn:de:0030-drops-170905},
  doi =		{10.4230/LIPIcs.CONCUR.2022.27},
  annote =	{Keywords: Hyperproperties, Asynchronous hyperproperties, Temporal logics for hyperproperties, Expressiveness, Decidability, Model checking}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2012.211
Visibly Rational Expressions

Authors: Laura Bozzelli and César Sánchez

Published in: LIPIcs, Volume 18, IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2012)

Abstract
Regular Expressions (RE) are an algebraic formalism for expressing regular languages, widely used in string search and as a specification language in verification. In this paper we introduce and investigate Visibly Rational Expressions (VRE), an extension of RE for the well-known class of Visibly Pushdown Languages (VPL). We show that VRE capture the class of VPL. Moreover, we identify an equally expressive fragment of VRE which admits a quadratic time compositional translation into the automata acceptors of VPL. We also prove that, for this fragment, universality, inclusion and language equivalence are EXPTIME-complete. Finally, we provide an extension of VRE for VPL over infinite words.
Cite as

Laura Bozzelli and César Sánchez. Visibly Rational Expressions. In IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2012). Leibniz International Proceedings in Informatics (LIPIcs), Volume 18, pp. 211-223, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2012)

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@InProceedings{bozzelli_et_al:LIPIcs.FSTTCS.2012.211,
  author =	{Bozzelli, Laura and S\'{a}nchez, C\'{e}sar},
  title =	{{Visibly Rational Expressions}},
  booktitle =	{IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2012)},
  pages =	{211--223},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-47-7},
  ISSN =	{1868-8969},
  year =	{2012},
  volume =	{18},
  editor =	{D'Souza, Deepak and Radhakrishnan, Jaikumar and Telikepalli, Kavitha},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2012.211},
  URN =		{urn:nbn:de:0030-drops-38604},
  doi =		{10.4230/LIPIcs.FSTTCS.2012.211},
  annote =	{Keywords: Visibly Pushdown Languages, Context-free specifications, Regular expressions, Algebraic characterization}
}
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