A Concurrent Perspective on Smart Contracts

Abstract

In this paper, we explore remarkable similarities between multi-transactional behaviors of smart contracts in cryptocurrencies such as Ethereum and classical problems of shared-memory concurrency. We examine two real-world examples from the Ethereum blockchain and analyzing how they are vulnerable to bugs that are closely reminiscent to those that often occur in traditional concurrent programs. We then elaborate on the relation between observable contract behaviors and well-studied concurrency topics, such as atomicity, interference, synchronization, and resource ownership. The described contracts-as-concurrentobjects analogy provides deeper understanding of potential threats for smart contracts, indicate better engineering practices, and enable applications of existing state-of-the-art formal verification techniques.

An overview on smart contracts: Challenges, advances and platforms

“…Liu et al [40] proposed to perform the fuzz testing on smart contracts by iteratively generating random but diverse transactions to detect reentrancy bugs. 1) Readability • Human readable code [34], [35] • Human readable execution [36], [37] • Re-entrancy [38], [39], [40] 2) Functional issues • Block randness [41], [42], [43] • Overcharging [44], [45] Deployment • Bytecode analysis [46], [47], [48], [49], [50], [51], [52], [53] 1) Contract correctness • Source code analysis [54], [55], [56], [57] • Machine learning based analysis [58], [59], [60] • Graph based analysis [61], [62] 2) Dynamic control flow • Path-searching [63] • Execution environment [64] Execution 1) Trustworthy oracle • Third-party involved [65] • Decentralized [66], [67] 2) Transaction-ordering dependence • Sequential execution [68] • Predefining contract [69] 3) Execution efficiency • Execution serialization [70], [71], [72] • Inspection of contract [73] Completion 1) Privacy and Security • Privacy [74],…”

“…In this way, conflicts happened during the parallel executions can be rolled back easily. Furthermore, the work in [71] investigated smart contracts in a concurrent perspective. In particular, concurrency issues such as atomicity, interference, synchronization, and resource ownership have been well studied in this paper.…”

Exploiting the laws of order in smart contracts

“…For instance, prior work has highlighted how a pair of transactions, when reordered, can cause contracts to exhibit differing Ether transfers as output [22]. Similarly, susceptibility of contracts to asynchronous callbacks has been identified previously [4], [34]. However, the full generality of bugs arising from unexpected ordering of eventsi.e.…”

Read-Uncommitted Transactions for Smart Contract Performance

“…Their programming languages are Turing complete [5] and their programs are called smart contracts [6]. Concurrency is framed in the words of Sergey and Hobor, "Accounts using smart contracts in a blockchain are like threads using concurrent objects in shared memory" [7]. Herlihy endorsed this line of reasoning in a keynote address [8], exhorting concurrency researchers to "civilize" the blockchain.…”

“…The FPV arguments in each buy include the previous mark, a hash that relates it to an interval between two sets. If a sequence occurs such as: set (5), buy (5), set (7), set (5), buy(5), a particular buy (5) can prove that it was sent during the first or the second interval the price was set to 5. Linking each buy transactions to a particular set price prevents the frontrunning attack mentioned in Section II-F.…”