Addressing the Tangle Vulnerability: A Preventive Strategy for IOTA by Using Large Deviation Theory.

IOTA is an emerging blockchain platform specially designed for the Internet of Things (IoT). It adopts a distributed ledger based on a directed acyclic graph (DAG) structure called the Tangle, achieving high concurrency, incremental scalability, and zero transaction fees. While the DAG-based ledger structure can promise many benefits for IOTA, it also exposes a wide attacking surface for the double-spending attack. By creating fake branches to replace the legitimate ones in the Tangle, the attackers can achieve the purpose of double-spending. Therefore, there is a great need for securing IOTA with preventive strategies. In this work, we present the design of an effective preventive strategy for IOTA that can reduce the Tangle vulnerability against the double-spending attack. Our main idea is to investigate the Tangle vulnerability problem by using the large deviation theory. We provide the Tangle vulnerability probability and the decay speed of the probability. By evaluating the decay speed, we find the key factor related to the robustness level against double-spending attacks. Besides, we define and deduce the security threshold based on the evaluation results that can affect the probability decay speed of the Tangle vulnerability. With the security threshold, IOTA can efficiently inspect illegal Tangle branches to resist double-spending attacks. Finally, the comprehensive theoretical analysis and simulation experiments demonstrate that the proposed strategy is efficient and practical.