# Direct Acyclic Graph based Ledger for Internet of Things: Performance and Security Analysis

## TL;DR

This paper analyzes the performance and security of DAG-based ledgers for IoT, focusing on how network load impacts confirmation delay and attack success probability, providing models for practical deployment guidance.

## Contribution

It introduces a Markov chain and stochastic model to analyze DAG consensus performance and security under dynamic network loads, which was previously unexplored.

## Key findings

- Network load significantly affects confirmation delay.
- Higher network load increases the probability of successful double-spending attacks.
- Trade-offs exist between security level and confirmation delay.

## Abstract

Direct Acyclic Graph (DAG)-based ledger and the corresponding consensus algorithm has been identified as a promising technology for Internet of Things (IoT). Compared with Proof-of-Work (PoW) and Proof-of-Stake (PoS) that have been widely used in blockchain, the consensus mechanism designed on DAG structure (simply called as DAG consensus) can overcome some shortcomings such as high resource consumption, high transaction fee, low transaction throughput and long confirmation delay. However, the theoretic analysis on the DAG consensus is an untapped venue to be explored. To this end, based on one of the most typical DAG consensuses, Tangle, we investigate the impact of network load on the performance and security of the DAG-based ledger. Considering unsteady network load, we first propose a Markov chain model to capture the behavior of DAG consensus process under dynamic load conditions. The key performance metrics, i.e., cumulative weight and confirmation delay are analysed based on the proposed model. Then, we leverage a stochastic model to analyse the probability of a successful double-spending attack in different network load regimes. The results can provide an insightful understanding of DAG consensus process, e.g., how the network load affects the confirmation delay and the probability of a successful attack. Meanwhile, we also demonstrate the trade-off between security level and confirmation delay, which can act as a guidance for practical deployment of DAG-based ledgers.