Directed Acyclic Graph‐Based Blockchain Performance Analysis and Its Secure Operation in Opportunistic Networks

Directed acyclic graph (DAG)‐based blockchain is a promising paradigm of a blockchain system. During DAG‐based consensus processes, nodes generate blocks in parallel, as well as voting YES on the previous blocks. It makes the DAG‐based blockchain a performance advantage in terms of confirmation delay and transaction throughput. However, Byzantine faults affect DAG‐based blockchain performance by not voting on blocks. The related analysis has not been explored. To this end, based on the most typical DAG‐based consensus mechanism with Byzantine Fault Tolerance, hashgraph, we investigate the resilience of the DAG‐based blockchain when Byzantine faults do not vote on blocks. First, we propose differential equations to model the running processes of the DAG‐based blockchain in both high‐load and low‐load networks. It reveals the impact of Byzantine nonvoting behaviors on blockchain performance in a mathematical manner. Second, Byzantine nonvoting adversaries can leave the target node orphaned in an opportunistic network of low‐load regimes. We propose a ranger‐assisted DAG‐based blockchain to alleviate the problem. It employs a group of rangers to collectively commit blocks and introduces the reputation, selection probabilities, and shuffling of rangers to supervise node behaviors. The performance of the proposed blockchain is also quantitatively analyzed. Third, we develop a blockchain simulator. The numerical results indicate the validity of the proposed analysis and the efficiency of the proposed blockchain.