Abstract: Although blockchain systems based on tree structures leverage the concurrency of tree graphs to significantly improve throughput,they still face numerous security challenges that need to be addressed.In response to the issue where such tree-based blockchain systems are vulnerable to liveness attacks,leading to a failure in ledger state convergence,a scalable and highly secure blockchain system called P-DAG(Parallel-Directed Acyclic Graph) is proposed,featuring high throughput and low confirmation latency.This system adopts a ledger structure with multiple parallel chains and decouples block creation from the process of adding blocks to the chain,thus distributing the computational power of malicious nodes to enhance the overall security of the system.By utilizing the randomness and uniform distribution properties of hash values,a hash-based random weight assignment mechanism is designed to reduce the convergence time of each chain and the block confirmation latency.Theoretical analysis and simulation experiments show that P-DAG achieves throughput similar to Conflux,but reduces ledger convergence time by approximately 50% and block confirmation latency by about 30% compared to Conflux.

Key words: Blockchain, Parallel chain, Directed acyclic graph, Liveness attack, Ledger convergence