Identifying Covert Channels in Blockchain: A Case Study on Bitcoin, Zcash, Monero and Ethereum

Blockchain has been an attractive platform both for covert channel and covert communication. Recent years have witnessed growing researches on achieving covert communication with blockchain applications. Identifying covert channels in blockchain is necessary and important to design blockchain based covert communication schemes. However, there still lacks a systematical method to analyze all possible covert channels in blockchain applications. In the paper, we propose a layer based covert channel identification method to analyze both covert storage channels and covert timing channels in blockchain applications. 11, 15, 14 and 19 new covert channels are identified in Bitcoin, Zcash, Monero and Ethereum with the proposed method, which proves the effectiveness of the method. The method is general and can be applied to identify covert channels in other blockchain applications, which lays foundation for both practical covert communication with blockchain applications and covert communication detection research.