Smart contracts have become lucrative and profitable targets for attackers because they can hold a great amount of money. Unfortunately, existing offline approaches for discovering the vulnerabilities in smart contracts or checking the correctness of smart contracts cannot conduct online detection of attacking transactions. Besides, existing online approaches only focus on specific attacks and cannot be easily extended to detect other attacks. Moreover, developing a new online detection system for smart contracts from scratch is time-consuming and requires deep understanding of blockchain internals, thus making it difficult to quickly implement and deploy mechanisms to detect new attacks. In this paper, we propose a novel generic online detection framework named SODA for smart contracts on any blockchains that support Ethereum virtual machine (EVM). SODA distinguishes itself from existing online approaches through its capability, efficiency, and compatibility. First, SODA empowers users to easily develop apps for detecting various attacks online (i.e., when attacks happen) by separating information collection and attack detection with layered design. At the higher layer, SODA provides unified interfaces to develop detection apps against various attacks. At the lower layer, SODA instruments EVM to collect all primitive information necessary to detect various attacks and constructs 11 kinds of structural information for the ease of developing apps. Based on SODA, users can develop new apps in a few lines of code without modifying EVM. Second, SODA is efficient, because we design on-demand information retrieval to reduce the overhead of information collection and adopt dynamic linking to eliminate the overhead of inter-process communication. Such design allows users to develop detection apps using any programming languages that can generate dynamic link libraries. Third, since more and more blockchains adopt EVM as smart contract runtime, SODA can be easily migrated to such blockchains without modifying apps. Based on SODA, we develop 8 detection apps to detect the attacks exploiting major vulnerabilities in smart contracts, and integrate SODA (including all apps) into 3 popular blockchains: Ethereum, Expanse and Wanchain. The extensive experimental results demonstrate the effectiveness and efficiency of SODA and our detection apps.

Electronic auction is a popular platform to sell goods, task assignment, and resources’ allocation due to reductions of transaction costs and has attracted a huge number of potential buyers. However, it is challenging to address the disputes between the buyer and the auctioneer. The main reason is, on the one hand, solving such problem leverages to the broad domain of research aspects, such as economic theory, engineering, and cryptography, and, on the other hand, it is difficult to arbitrate in a decentralized and anonymous setting. In this work, we consider a more general framework to solve the potential disputes by enforcing bidirectional confirmation and public verification. Hence, the bidding procedure is clear to inspect and potential disputes can be erased. To achieve this goal, we propose policy-driven chameleon hash and revised linkable-and-redactable ring signature as building blocks. We used these two tools to build a bidirectional and anonymous auction protocol called BA 2 P. In our BA 2 P protocol, the bidders can competitively and anonymously place their bids to outbid others. At the end of the auction protocol, everyone can verify the validity of the bidding proof and decide the winner. Thus, dispute-freeness feature is achieved. The analysis suggests that our proposal is provably secure and practically efficient, and it trades some efficiencies with dispute-freeness feature.

Millions of smart contracts have been deployed onto Ethereum for providing various services, whose functions can be invoked. For this purpose, the caller needs to know the function signature of a callee, which includes its function id and parameter types. Such signatures are critical to many applications focusing on smart contracts, e.g., reverse engineering, fuzzing, attack detection, and profiling. Unfortunately, it is challenging to recover the function signatures from contract bytecode, since neither debug information nor type information is present in the bytecode. To address this issue, prior approaches rely on source code, or a collection of known signatures from incomplete databases or incomplete heuristic rules, which, however, are far from adequate and cannot cope with the rapid growth of new contracts. In this paper, we propose a novel solution that leverages how functions are handled by Ethereum virtual machine (EVM) to automatically recover function signatures. In particular, we exploit how smart contracts determine the functions to be invoked to locate and extract function ids, and propose a new approach named type-aware symbolic execution (TASE) that utilizes the semantics of EVM operations on parameters to identify the number and the types of parameters. Moreover, we develop SigRec, a new tool for recovering function signatures from contract bytecode without the need of source code and function signature databases. The extensive experimental results show that SigRec outperforms all existing tools, achieving an unprecedented 98.7% accuracy within 0.074 seconds. We further demonstrate that the recovered function signatures are useful in attack detection, fuzzing and reverse engineering of EVM bytecode.

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Being the most popular programming language for developing Ethereum smart contracts, Solidity allows using inline assembly to gain fine-grained control. Although many empirical studies on smart contracts have been conducted, to the best of our knowledge, none has examined inline assembly in smart contracts. To fill the gap, in this paper, we conduct the first large-scale empirical study of inline assembly on more than 7.6 million open-source Ethereum smart contracts from three aspects, namely, source code, bytecode, and transactions after designing new approaches to tackle several technical challenges. Through a thorough quantitative and qualitative analysis of the collected data, we obtain many new observations and insights. Moreover, by conducting a questionnaire survey on using inline assembly in smart contracts, we draw new insights from the valuable feedback. This work sheds light on the development of smart contracts as well as the evolution of Solidity and its compilers.