Boros: Secure and Efficient Off-Blockchain Transactions via Payment Channel Hub

Payment channel, which allows two parties to perform micropayments without involving the blockchain, has become a promising proposal to improve the scalability of decentralized ledgers. Payment channels have been extended to payment networks to utilize existing channels as intermediary links to route coins to others. However, payments through multiple channels bear nontrivial overheads, including time cost, charges at intermediate nodes, etc. In this paper, we propose channel hub, a novel off-chain system to shorten the routing path for the payment network. Channel hub allows transferring coins directly from one payment channel to another within the same hub, so that it can be viewed as a shortcut device for the underlying payment network. Compared with payment hub in literature, which connects participant nodes, our channel hub is more efficient and lightweight, because it connects channels already constructed by the payment network. Based on channel hub, we design a new protocol named Boros to perform secure off-chain cross-channel transfers. We present the security definition of Boros and formally prove its security using the UC-framework. To demonstrate the feasibility of Boros, we develop a proof-of-concept prototype running on Ethereum. Performance evaluation shows that Boros can effectively shorten the off-chain payment path.