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.

We present EverCrypt: a comprehensive collection of verified, high-performance cryptographic functionalities available via a carefully designed API. The API provably supports agility (choosing between multiple algorithms for the same functionality) and multiplexing (choosing between multiple implementations of the same algorithm). Through abstraction and zero-cost generic programming, we show how agility can simplify verification without sacrificing performance, and we demonstrate how C and assembly can be composed and verified against shared specifications. We substantiate the effectiveness of these techniques with new verified implementations (including hashes, Curve25519, and AES-GCM) whose performance matches or exceeds the best unverified implementations. We validate the API design with two high-performance verified case studies built atop EverCrypt, resulting in line-rate performance for a secure network protocol and a Merkle-tree library, used in a production blockchain, that supports 2.7 million insertions/sec. Altogether, EverCrypt consists of over 124K verified lines of specs, code, and proofs, and it produces over 29K lines of C and 14K lines of assembly code. SpecificationsImplementations Spec.Hash val compress (a:alg) (st:words a) (b:block a) : words_state a val init val finish val compress_many val hash EverCrypt.Hash val compress (st:state alg) (b:larr uint8 alg) : Stack unit (requires fun h0 -> ...) (ensures fun h0 _ h1 -> ... /\ repr s h1 == Spec.Hash.compress alg (repr s h0) (as_seq h0 b))val init, finish, compress_many, hash Refines Spec.MD5 val compress: ... val init: ...

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Cryptocurrencies have popularized public ledgers, known colloquially as "blockchains". While the Bitcoin blockchain is relatively simple to reason about as, effectively, a hash chain, more complex public ledgers are largely designed without any formalization of desired cryptographic properties such as authentication or integrity. These designs are then implemented without assurances against real-world bugs leading to little assurance with regards to practical, real-world security.Ledger Design Language (LDL) is a modeling language for describing public ledgers. The LDL compiler produces two outputs. The first output is a an applied-pi calculus symbolic model representing the public ledger as a protocol. Using ProVerif, the protocol can be played against an active attacker, whereupon we can query for block integrity, authenticity and other properties. The second output is a formally verified read/write API for interacting with the public ledger in the real world, written in the F ⋆ programming language. F ⋆ features such as dependent types allow us to validate a block on the public ledger, for example, by type-checking it so that its signing public key be a point on a curve. Using LDL's outputs, public ledger designers obtain automated assurances on the theoretical coherence and the real-world security of their designs with a single framework based on a single modeling language.

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