Millions of contracts deployed onto Ethereum provide various services that can be invoked. For this purpose, blockchain users need to know and specify the function signature of a callee, which includes its function id and the parameter types. Function signatures are crucial in several applications, such as recognizing the services that contracts provide. In this poster, we propose a novel solution that leverages how functions are handled by Ethereum virtual machine (EVM) to automatically recover function signatures from contract bytecode, without the need of source code and function signature databases. The extensive experimental results show that our solution outperforms all existing tools, achieving an unprecedented 98.7% accuracy within 0.074 seconds. We further demonstrate the usefulness of our solution in attack detection, fuzzing and reverse engineering of contract bytecode.

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 thefunction signatureof a callee, which includes its function id and parameter types. Such signatures arecriticalto 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 namedtype-awaresymbolic execution (TASE) that utilizes the semantics of EVM operations on parameters to identify the number and the types of parameters. Moreover, we developSigRec, 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 thatSigRecoutperforms all existing tools, achieving an unprecedented 98.7 percent 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.