Securing Wireless Payment-Channel Networks With Minimum Lock Time Windows

Abstract

Payment-channel networks (PCN) enhance the impact of cryptocurrencies by providing a fast and consensus-free solution to the scalability problems of traditional blockchain protocols. However, PCNs often rely on powerful nodes with high availability, large storage capacity, and strong computational power, which hinders their adoption in mobile environments. In this paper, we consider a PCN architecture that extends the functionalities of traditional PCNs to wireless resource-constrained devices. We address the token theft problem, a vulnerability that is critical on wireless PCNs, and propose a countermeasure based on minimum time windows that lock tokens whenever a user disconnects. We evaluate our proposal with real data from Bitcoin's Lightning Network and 3G/4G mobile broadband networks. The results show that the countermeasure is most effective when devices present high availability and that there is a security-efficiency trade-off when connectivity is low. I. INTRODUCTIONPayment channels and payment-channel networks offer a scalable and efficient off-chain solution to improve the performance of blockchain-based systems. To open a payment channel, two users sign and publish a funding transaction that transfers a fixed amount of tokens to a joint address in the blockchain. The users can then continuously rebalance the funds of the address by sending private signed commitment transactions, as shown in Figure 1. This way, both parties transact with each other without paying the blockchain fees and waiting for the system to approve the transactions through consensus. To close the channel, either user publishes the last commitment transaction into the blockchain and waits for the lock time window 1 to recover their tokens. The lock time window serves as a security mechanism to prevent a user from stealing tokens when the other party disconnects. We explain this process in detail in Section III.A payment-channel network (PCN) is the collection of payment channels that form a peer-to-peer network for token transfers. In PCNs, nodes can issue payments to destinations even if they do not share a payment channel. For example, in Figure 2, if Alice wants to send one token to Charlie, she can send the token to Bob, and Bob relays it to Charlie. Bob receives the token from Alice once he sends one token of his own to Charlie through Hashed Timelock Contracts 1 The lock time window is often referred to as "to self delay" or "return delay" in the literature [1], [2]. We consider the terms equivalent.