Griefing-Penalty: Countermeasure for Griefing Attack in Lightning Network

TL;DR

This paper introduces Griefing-Penalty, a countermeasure for griefing attacks in the Lightning Network, by penalizing attackers proportionally to their collateral cost, thereby reducing attack profitability and enhancing network security.

Contribution

The paper proposes HTLC-GP, a new payment protocol incorporating griefing penalties, and demonstrates its effectiveness in decreasing attacker revenue and increasing attack costs.

Findings

Attacker revenue decreases significantly with HTLC-GP.

The required attack budget is 12 times higher with HTLC-GP.

Longer routing paths increase the attacker's cost.

Abstract

Lightning Network can execute unlimited number of off-chain payments, without incurring the cost of recording each of them in the blockchain. However, conditional payments in such networks is susceptible to Griefing Attack. In this attack, an adversary doesn't resolve the payment with the intention of blocking channel capacity of the network. We propose an efficient countermeasure for the attack, known as Griefing-Penalty. If any party in the network mounts a griefing attack, it needs to pay a penalty proportional to the collateral cost of executing a payment. The penalty is used for compensating affected parties in the network. We propose a new payment protocol HTLC-GP or Hashed Timelock Contract with Griefing-Penalty to demonstrate the utility of the countermeasure. Upon comparing our protocol with existing payment protocol Hashed Timelock Contract, we observe that the average revenue earned by the attacker decreases substantially for HTLC-GP as compared to HTLC. We also study the impact of path length for routing a transaction and rate of griefing-penalty on the budget invested by an adversary for mounting the attack. The budget needed for mounting griefing attack in HTLC-GP is 12 times more than the budget needed by attacker in HTLC, given that each payment instance being routed via path length of hop count 20.