On the Security of Permissionless Blockchain Systems: Challenges and Research Perspective

Blockchain technology enables global mutually trustless participants to reach a consensus on the final state of permissionless distributed and decentralized ledgers. Due to its properties of openness, transparency, irreversibility, and credibility, many systems have been built based on blockchains' structure, such as Bitcoin and Ethereum. With the wide application of blockchains, however, many security problems still exist in blockchains and there have been many malicious attacks against blockchain systems. Although these attacks have been proposed, there lacks a systematic exploration of how these attacks have been conducted and what underlying relationship they have. In this paper, we firstly present and summarize several current attacks on blockchains in three aspects: system deficiency attacks, mining attacks, and network-level attacks. Secondly, we conduct a systematic analysis and evaluation of the possibility of these attacks occurring on major blockchain platforms. Finally, we motivate some research perspectives and challenges for blockchain system security and highlight some potential solutions to these problems.

I. Introduction

Bitcoin [1], as well as its underlying technology blockchain, has made great strides in the past decade and its market value has reached more than trillion. This success is mainly driven by its peculiarities: decentralization: millions of nodes from all over the world work for the same community; consensus: all the nodes will eventually agree on a final state of the ledge; transparency and openness: all the transactions on the chain, including the addresses of participants, are recorded on the blocks and can be accessed by all participants; append-only: transactions which have been chained cannot be modified or deleted; robustness: the system is strong and self-adjusting and it can tolerate a large fraction of faulty problems. In addition to bitcoin, blockchain platforms with more models and functions are also growing like Ethereum, which proposed a new mode called Smart Contract.