Ethereum is a framework for cryptocurrencies which uses blockchain technology to provide an open global computing platform, called the Ethereum Virtual Machine (EVM). EVM executes bytecode on a simple stack machine. Programmers do not usually write EVM code; instead, they can program in a JavaScript-like language, called Solidity, that compiles to bytecode. Since the main purpose of EVM is to execute smart contracts that manage and transfer digital assets (called Ether), security is of paramount importance. However, writing secure smart contracts can be extremely difficult: due to the openness of Ethereum, both programs and pseudonymous users can call into the public methods of other programs, leading to potentially dangerous compositions of trusted and untrusted code. This risk was recently illustrated by an attack on TheDAO contract that exploited subtle details of the EVM semantics to transfer roughly $50M worth of Ether into the control of an attacker. In this paper, we outline a framework to analyze and verify both the runtime safety and the functional correctness of Ethereum contracts by translation to F , a functional programming language aimed at program verification.

Web sites that accept and display content such as wiki articles or comments typically filter the content to prevent injected script code from running in browsers that view the site. The diversity of browser rendering algorithms and the desire to allow rich content make filtering quite difficult, however, and attacks such as the Samy and Yamanner worms have exploited filtering weaknesses. This paper proposes a simple alternative mechanism for preventing script injection called Browser-Enforced Embedded Policies (BEEP). The idea is that a web site can embed a policy in its pages that specifies which scripts are allowed to run. The browser, which knows exactly when it will run a script, can enforce this policy perfectly. We have added BEEP support to several browsers, and built tools to simplify adding policies to web applications. We found that supporting BEEP in browsers requires only small and localized modifications, modifying web applications requires minimal effort, and enforcing policies is generally lightweight.

We present a new, completely redesigned, version of F ⋆ , a language that works both as a proof assistant as well as a general-purpose, verification-oriented, effectful programming language. In support of these complementary roles, F ⋆ is a dependently typed, higher-order, call-by-value language with primitive effects including state, exceptions, divergence and IO. Although primitive, programmers choose the granularity at which to specify effects by equipping each effect with a monadic, predicate transformer semantics. F ⋆ uses this to efficiently compute weakest preconditions and discharges the resulting proof obligations using a combination of SMT solving and manual proofs. Isolated from the effects, the core of F ⋆ is a language of pure functions used to write specifications and proof terms-its consistency is maintained by a semantic termination check based on a well-founded order. We evaluate our design on more than 55,000 lines of F ⋆ we have authored in the last year, focusing on three main case studies. Showcasing its use as a general-purpose programming language, F ⋆ is programmed (but not verified) in F ⋆ , and bootstraps in both OCaml and F#. Our experience confirms F ⋆ 's pay-as-you-go cost model: writing idiomatic ML-like code with no finer specifications imposes no user burden. As a verification-oriented language, our most significant evaluation of F ⋆ is in verifying several key modules in an implementation of the TLS-1.2 protocol standard. For the modules we considered, we are able to prove more properties, with fewer annotations using F ⋆ than in a prior verified implementation of TLS-1.2. Finally, as a proof assistant, we discuss our use of F ⋆ in mechanizing the metatheory of a range of lambda calculi, starting from the simply typed lambda calculus to System F ω and even µF ⋆ , a sizeable fragment of F ⋆ itself-these proofs make essential use of F ⋆ 's flexible combination of SMT automation and constructive proofs, enabling a tactic-free style of programming and proving at a relatively large scale. Categories and Subject Descriptors D.3.1 [Programming Languages]: Formal Definitions and Theory-Semantics; F.3.1 [Logics and Meanings of Programs]: Specifying and Verifying and Reasoning about Programs-Mechanical verification Keywords verification; proof assistants; effectful programming 1 Henceforth, we refer to the new language presented in this paper as "F ⋆ " while referring to the old, defunct version as "old-F ⋆ ".

Distributed applications are difficult to program reliably and securely. Dependently typed functional languages promise to prevent broad classes of errors and vulnerabilities, and to enable program verification to proceed side-by-side with development. However, as recursion, effects, and rich libraries are added, using types to reason about programs, specifications, and proofs becomes challenging.We present F , a full-fledged design and implementation of a new dependently typed language for secure distributed programming. Unlike prior languages, F provides arbitrary recursion while maintaining a logically consistent core; it enables modular reasoning about state and other effects using affine types; and it supports proofs of refinement properties using a mixture of cryptographic evidence and logical proof terms. The key mechanism is a new kind system that tracks several sub-languages within F and controls their interaction. F subsumes two previous languages, F7 and Fine. We prove type soundness (with proofs mechanized in Coq) and logical consistency for F .We have implemented a compiler that translates F to .NET bytecode, based on a prototype for Fine. F provides access to libraries for concurrency, networking, cryptography, and interoperability with C#, F#, and the other .NET languages. The compiler produces verifiable binaries with 60% code size overhead for proofs and types, as much as a 45x improvement over the Fine compiler, while still enabling efficient bytecode verification.To date, we have programmed and verified more than 20,000 lines of F including (1) new schemes for multi-party sessions;(2) a zero-knowledge privacy-preserving payment protocol; (3) a provenance-aware curated database; (4) a suite of 17 web-browser extensions verified for authorization properties; and (5) a cloudhosted multi-tier web application with a verified reference monitor.

Relational program logics have been used for mechanizing formal proofs of various cryptographic constructions. With an eye towards scaling these successes towards end-to-end security proofs for implementations of distributed systems, we present RF , a relational extension of F , a general-purpose higher-order stateful programming language with a verification system based on refinement types. The distinguishing feature of RF is a relational Hoare logic for a higher-order, stateful, probabilistic language. Through careful language design, we adapt the F typechecker to generate both classic and relational verification conditions, and to automatically discharge their proofs using an SMT solver. Thus, we are able to benefit from the existing features of F , including its abstraction facilities for modular reasoning about program fragments. We evaluate RF experimentally by programming a series of cryptographic constructions and protocols, and by verifying their security properties, ranging from information flow to unlinkability, integrity, and privacy. Moreover, we validate the design of RF by formalizing in Coq a core probabilistic λ-calculus and a relational refinement type system and proving the soundness of the latter against a denotational semantics of the probabilistic λ-calculus.

No abstract

No abstract

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.