Defining the Ethereum Virtual Machine for Interactive Theorem Provers

Ethereum smart contracts are programs that run on the Ethereum blockchain, and many smart contract vulnerabilities have been discovered in the past decade. Many security analysis tools have been created to detect such vulnerabilities, but their performance decreases drastically when codes to be analyzed are being rewritten. In this paper, we propose Eth2Vec, a machine-learning-based static analysis tool for vulnerability detection, with robustness against code rewrites in smart contracts. Existing machine-learning-based static analysis tools for vulnerability detection need features, which analysts create manually, as inputs. In contrast, Eth2Vec automatically learns features of vulnerable Ethereum Virtual Machine (EVM) bytecodes with tacit knowledge through a neural network for language processing. Therefore, Eth2Vec can detect vulnerabilities in smart contracts by comparing the code similarity between target EVM bytecodes and the EVM bytecodes it already learned. We conducted experiments with existing open databases, such as Etherscan, and our results show that Eth2Vec outperforms the existing work in terms of well-known metrics, i.e., precision, recall, and F1-score. Moreover, Eth2Vec can detect vulnerabilities even in rewritten codes.

Blockchain technology has increasing attention in research and across many industries. The Ethereum blockchain offers smart contracts, which are small programs defined, executed, and recorded as transactions in the blockchain transaction history. These smart contracts run on the Ethereum Virtual Machine (EVM) and can be used to encode agreements, transfer assets, and enforce integrity conditions in relationships between parties. Smart contracts can carry financial value, and are increasingly used for safety-, security-, or mission-critical purposes. Errors in smart contracts have led and will lead to loss or harm. Formal verification can provide the highest level of confidence about the correct behaviour of smart contracts. In this paper we extend an existing EVM formalisation in Isabelle/HOL by a sound program logic at the level of bytecode. We structure bytecode sequences into blocks of straight-line code and create a program logic to reason about these. This abstraction is a step towards control of the cost and complexity of formal verification of EVM smart contracts.

Integer overflow is a common vulnerability in Ethereum Smart Contracts (ESCs) and often causes huge economic losses. Smart contracts cannot be changed once it is deployed on the blockchain and thus demand further testing. Mutation testing is a fault-based testing method that can effectively improve the sufficiency of a test for smart contracts. However, existing methods cannot efficiently perform mutation testing specifically for integer overflow in ESCs. Therefore, by analyzing integer overflow in ESCs, we propose five special mutation operators to address such vulnerability in terms of detecting sufficiency in ESC testing. An empirical study on 40 open-source ESCs is conducted to evaluate the effectiveness of the proposed mutation operators. Results show that: (1) our proposed mutation operators can reproduce all 179 integer overflow vulnerabilities in 40 smart contracts, and the generated mutants have high compilation pass rate and integer overflow vulnerability generation rate; moreover, (2) the generated mutants can find the shortcomings of existing testing methods for integer overflow vulnerability, thereby providing effective support to improve the sufficiency of the test.

The immutable nature of Ethereum transactions, and consequently Ethereum smart-contracts, has stimulated the proliferation of many approaches aiming at detecting defects and security issues before the deployment of smart-contracts on the blockchain. Indeed, the actions performed by smart-contracts instantiated on the blockchain, possibly involving substantial financial value, cannot be undone.Unfortunately, smart-contracts source code is not always available, hence approaches based on static analysis have very often to face the problem of inspecting the compiled Ethereum Virtual Machine (EVM) bytecode, retrieved directly from the blockchain. However, due to the intrinsic complexity of EVM bytecode (especially in jumps address resolution), the state-of-the-art static analysis-based solutions have poor accuracy in the automated detection of Ethereum smart-contracts programming defects and vulnerabilities.This paper presents a novel approach based on symbolic execution of the EVM operands stack that allows to resolve jumps address in the EVM bytecode and to construct a precise Control-Flow Graph (CFG) of compiled smart-contracts. Many static analysis techniques are based on a CFG-based representation of the smart-contract to validate, and would therefore benefit from our approach.We have implemented the CFG reconstruction algorithm in a tool called EtherSolve . Then, we have validated the tool on a large dataset of real-world Ethereum smart-contracts, showing that EtherSolve extracts more precise CFGs, w.r.t. state-of-the-art available approaches. Finally, we have extended EtherSolve with two detectors for two of the most prominent Ethereum smart-contracts vulnerabilities (Reentrancy and Tx.origin). Experimental results show that exploiting the proposed CFG reconstruction static analysis, leads to more accurate vulnerabilities detection, w.r.t. state-of-the-art security tools.Editor’s note: Open Science material was validated by the Journal of Systems and Software Open Science Board.

The Web public-key infrastructure (PKI) provides a mechanism to identify websites to end users for the purposes of encrypted communication. The security of the Web PKI primarily relies on certification authorities (CAs), trusted parties whose misbehavior can enable man-in-the-middle (MITM) attacks: the impersonation of websites to users, followed by the theft or modification of sensitive information. While many methods of addressing CA misbehavior have been proposed, no solution has been both effective and practical: able to protect websites users against C misbehavior and to be easily deployed and used by all parties involved. Thus, despite more than two decades of research advances, the Web PKI remains largely vulnerable to misbehaving CAs.In this thesis, I argue that we can use minimal changes to existing technology to build deployable solutions thatreduce the rate of successful MITM attacks in the Web PKI. Specifically, I present three projects that exemplifyeffective and practical approaches to improving the Web PKI. In IKP, I use the Ethereum cryptocurrency and smartcontract platform to build an insurance-like mechanism that disincentivizes CA misbehavior. In CAPS, I use twoglobal monitoring and logging systems, CT and Censys, to build a system that strengthens the existing PKI againstmisbehaving CAs and enables the secure incremental deployment of new and improved PKIs for theWeb. In SAINT, I use the SCION future Internet architecture to propose a PKI that unifies public-key authentication for naming, routing, and end-entity public keys in a federated environment, and identify challenges and desired properties in such an environment. Through this work, I provide a first step towards making a more resilient Web PKI a reality.

Ethereum smart contracts are computer programs that are deployed and executed on the Ethereum blockchain to enforce agreements among untrusting parties. Being the most prominent platform that supports smart contracts, Ethereum has been targeted by many attacks and plagued by security incidents. Consequently, many smart contract vulnerabilities have been discovered in the past decade. To detect and prevent such vulnerabilities, different security analysis tools, including static and dynamic analysis tools, have been created, but their performance decreases drastically when codes to be analyzed are constantly being rewritten. In this paper, we propose Eth2Vec, a machine-learning-based static analysis tool that detects smart contract vulnerabilities. Eth2Vec maintains its robustness against code rewrites; i.e., it can detect vulnerabilities even in rewritten codes. Other machine-learning-based static analysis tools require features, which analysts create manually, as inputs. In contrast, Eth2Vec uses a neural network for language processing to automatically learn the features of vulnerable contracts. In doing so, Eth2Vec can detect vulnerabilities in smart contracts by comparing the similarities between the codes of a target contract and those of the learned contracts. We performed experiments with existing open databases, such as Etherscan, and Eth2Vec was able to outperform a recent model based on support vector machine in terms of well-known metrics, i.e., precision, recall, and F1-score.

Blockchain technology and its applications are gaining popularity day by day. It is a ground-breaking technology that allows users to communicate without the need of a trusted middleman. A smart contract (self-executable code) is deployed on the blockchain and auto executes due to a triggering condition. In a no-trust contracting environment, smart contracts can establish trust among parties. Terms and conditions embedded in smart contracts will be imposed immediately when specified criteria have been fulfilled. Due to this, the malicious assailants have a special interest in smart contracts. Blockchains are immutable means if some transaction is deployed or recorded on the blockchain, it becomes unalterable. Thus, smart contracts must be analyzed to ensure zero security vulnerabilities or flaws before deploying the same on the blockchain because a single vulnerability can lead to the loss of millions. For analyzing the security vulnerabilities of smart contracts, various analysis tools have been developed to create safe and secure smart contracts. This paper presents a systematic review on Ethereum smart contracts analysis tools. Initially, these tools are categorized into static and dynamic analysis tools. Thereafter, different sources code analysis techniques are studied such as taint analysis, symbolic execution, and fuzzing techniques. In total, 86 security analysis tools developed for Ethereum blockchain smart contract are analyzed regardless of tool type and analysis approach. Finally, the paper highlights some challenges and future recommendations in the field of Ethereum smart contracts.

Smart contract (SC) is an extension of BlockChain technology. Ethereum BlockChain was the first to incorporate SC and thus started a new era of crypto-currencies and electronic transactions. Solidity helps to program the SCs. Still, soon after Solidity's emergence in 2014, Solidity-based SCs suffered many attacks that deprived the SC account holders of their precious funds. The main reason for these attacks was the presence of vulnerabilities in SC. This paper discusses SC vulnerabilities and classifies them according to the domain knowledge of the faulty operations. This classification is a source of reminding developers and software engineers that for SC's safety, each SC requires proper testing with effective tools to catch those classes' vulnerabilities.

Permissionless blockchain-enabled smart contracts that use the proof-of-stake (PoS) algorithm for validation of transactions have scalability and on-chain governance as a primary concern. We consider smart contracts that use lite mobile wallets with support of the unspent transaction output protocol (UTXO) and simple payment verification (SPV) to increase the number of transaction throughput. Furthermore, we investigate in this paper to which extent it is possible to change the parameters of the blockchain using smart contracts in hot parameter swaps at runtime for enabling continuous soft forks. The leading smart contract solution Ethereum does not have the functionality to change blockchain parameters and requires hard forks multiple times, and thus, Ethereum smart contracts are not scalable for large industrial applications. This whitepaper fills the gap by presenting the Qtum’s decentralized-governance protocol (DGP) that aims for managing essential blockchain parameters using smart contracts for enabling frequent soft forks. Compared with the Ethereum alternative, we explore the Qtum utility advantages and current Qtum smart contract future development plans integrating dedicated x86 hardware development for industry case applications.KeywordsSmart contractBlockchainMobileLite walletPoSAbstraction layerSVPUTXODecentralized governance

The inception of blockchain techniques has been revolutionizing various domains, e.g., Internet of Things, supply chain and healthcare. Ethereum smart contracts emerge as the promising blockchain application, which could enable distrustful parties to participate in the automatic and trustful transactions. Given the increasing importance of Ethereum smart contracts, understanding them becomes imperative. However, prior work only studied smart contracts with general high-level patterns, and one critical question has not been answered yet: how do smart contracts behave individually? In this paper, we present a behavior-aware profiling of individual smart contract from a multi-party perspective, which improves the visibility of the smart contract ecosystem. We conduct a detailed study of the behavior of individual smart contract on two real-world datasets, and our profiling reveals interesting and surprising observations. For example, a few contract completion chains have more than 50 contracts and all of them belong to the Finance category. We also discuss the implications that lead to recommendations to improve the security and performance of the smart contract ecosystem. Overall, our work effectively complements previous work towards generating a comprehensive understanding of smart contracts.

In recent years, Ethereum gained tremendously in popularity, growing from a daily transaction average of 10K in January 2016 to an average of 500K in January 2020. Similarly, smart contracts began to carry more value, making them appealing targets for attackers. As a result, they started to become victims of attacks, costing millions of dollars. In response to these attacks, both academia and industry proposed a plethora of tools to scan smart contracts for vulnerabilities before deploying them on the blockchain. However, most of these tools solely focus on detecting vulnerabilities and not attacks, let alone quantifying or tracing the number of stolen assets. In this paper, we present Horus, a framework that empowers the automated detection and investigation of smart contract attacks based on logic-driven and graph-driven analysis of transactions. Horus provides quick means to quantify and trace the flow of stolen assets across the Ethereum blockchain. We perform a large-scale analysis of all the smart contracts deployed on Ethereum until May 2020. We identified 1,888 attacked smart contracts and 8,095 adversarial transactions in the wild. Our investigation shows that the number of attacks did not necessarily decrease over the past few years, but for some vulnerabilities remained constant. Finally, we also demonstrate the practicality of our framework via an in-depth analysis on the recent Uniswap and Lendf.me attacks.KeywordsEthereumSmart contractsAttack detectionForensics

Cryptocurrencies record transactions in a decentralized data structure called a blockchain. Two of the most popular cryptocurrencies, Bitcoin and Ethereum, support the feature to encode rules or scripts for processing transactions. This feature has evolved to give practical shape to the ideas of smart contracts, or full-fledged programs that are run on blockchains. Recently, Ethereum's smart contract system has seen steady adoption, supporting tens of thousands of contracts, holding millions dollars worth of virtual coins. In this paper, we investigate the security of running smart contracts based on Ethereum in an open distributed network like those of cryptocurrencies. We introduce several new security problems in which an adversary can manipulate smart contract execution to gain profit. These bugs suggest subtle gaps in the understanding of the distributed semantics of the underlying platform. As a refinement, we propose ways to enhance the operational semantics of Ethereum to make contracts less vulnerable. For developers writing contracts for the existing Ethereum system, we build a symbolic execution tool called Oyente to find potential security bugs. Among 19, 336 existing Ethereum contracts, Oyente flags 8, 833 of them as vulnerable, including the TheDAO bug which led to a 60 million US dollar loss in June 2016. We also discuss the severity of other attacks for several case studies which have source code available and confirm the attacks (which target only our accounts) in the main Ethereum network.

Smart contracts are computer programs designed to automate legal agreements. They are usually developed in a high-level programming language, the most popular of which is Solidity. Every day, hundreds of thousands of new contracts are deployed managing millions of dollars’ worth of transactions. As for every computer program, smart contracts may contain bugs which can be exploited. However, since smart contracts are often used to automate financial transactions, such exploits may result in huge economic losses. In general, it is estimated that since 2019, more than $5B was stolen due to vulnerabilities in smart contracts. This article addresses the issue of smart contract vulnerabilities by introducing an executable denotational semantics for Solidity within the Isabelle/HOL interactive theorem prover. This formal semantics serves as the basis for an interactive program verification environment for Solidity smart contracts. To evaluate our semantics, we integrate grammar-based fuzzing with symbolic execution to automatically test it against the Solidity reference implementation. The article concludes by showcasing the formal verification of Solidity programs, exemplified through the verification of a basic Solidity token.

Ethereum holds multiple billions of U.S. dollars in the form of Ether cryptocurrency and ERC-20 tokens, with millions of deployed smart contracts algorithmically operating these funds. Unsurprisingly, the security of Ethereum smart contracts has been under rigorous scrutiny. In recent years, numerous defense tools have been developed to detect different types of smart contract code vulnerabilities. When opportunities for exploiting code vulnerabilities diminish, the attackers start resorting to social engineering attacks, which aim to influence humans - often the weakest link in the system. The only known class of social engineering attacks in Ethereum are honeypots, which plant hidden traps for attackers attempting to exploit existing vulnerabilities, thereby targeting only a small population of potential victims.

As Ethereum's smart contracts have boomed, it has become an integral part of the blockchain ecosystem. Unfortunately, some malicious users also find the opportunity to use fraudulent means to profit. A new reported approach is to lure new users or other attackers into the contract in an attempt to make a profit by exposing seemingly obvious flaws in the contract. But in fact, the contract contains a hidden trap that ultimately benefits the creator of the contract. Such contracts are known as honeypot contracts in the blockchain ecosystem. Previous studies proposed two methods to identify such smart contracts by using symbolic execution and contract behaviors. However, these methods either make it difficult to discover new categories or fail to warn users before they lose money. To solve this problem, we propose a machine learning model to detect honeypot contracts based on N-gram features and LightGBM. Extensive experiments show that our proposed model performs well in different conditions.