Payment Privacy Protection Of The Bitcoin Lightning Network

Blockchain-based cryptocurrencies are inherently limited in the problem of scalability.However,the solutions by directly modifying parameters within a blockchain will affect the security of the blockchain system.As a viable solution,payment channel networks enable low latency and high throughput of payments without changing the blockchain consensus.The Lightning Network based on Bitcoin blockchain is currently the largest payment channel network.The transactions in the Lightning Network require the pathfinding phase and the payment phase.Since users in the Lightning Network cannot publish channel balance information to preserve privacy properties,it is difficult to determine a payment path with sufficient funds that can connect the payer and the payee during the pathfinding phase.The existing pathfinding schemes face the problems of low efficiency and inability to protect payment privacy such as the identity of both the receiver and the sender in a payment.Moreover,in the payment phase of the Lighting Network,payments often fail due to the deadlock on payment channel.Considering the above problems of transactions in the Lightning Network,the main contributions of this thesis are as follows:Firstly,this thesis proposes a pathfinding scheme in the Lightning Network to protect payment privacy.The basic idea of this scheme is that users submit channel information such as balances of payment channel to the path provider,which responds to users' pathfinding request.The centralized pathfinding method reduces user overhead.This scheme employs Intel Software Guard Extensions(SGX)to prevent the path provider from obtaining sensitive information during pathfinding.Due to the vulnerability of SGX,this scheme introduces Oblivious Random Access Machine(ORAM)to protect the access pattern of SGX.To avoid single point of failure,this scheme designs attestation between multiple SGXs.The security analysis shows that this scheme can protect payment privacy and the experiment denotes that the efficiency of pathfinding has been improved.Secondly,this thesis proposes a hierarchical pathfinding scheme in the Lighting Network.Users in the Lighting Network are naturally divided into multiple communities,so this scheme designs a pathfinding protocol between communities.There is a path provider with a group of SGXs responding to the pathfinding requests within each community,and an additional SGX layer is implemented on top of those path providers for the requests across communities.Based on the hierarchical framework,the efficiency of frequent pathfinding requests within every community has been improved and the connectivity of any two users in the lightning network can be ensured.The security analysis and the evaluation show that the efficiency of the pathfinding is improved without comprising users' payment privacyFinally,this thesis designs an anti-theft anonymous payment intermediary,which uses SGX to establish payment channels with multiple users.Users can complete offchain payments with each other through the payment intermediary.The anonymous payment intermediary shortens the payment path in the the Lighting Network to two hops,which greatly improves payment efficiency.The payment paths between different payer and payee will not contain the same channel,which solves the deadlock problem in the payment phase of the Lightning Network.As the transaction is executed by SGX and the funds are not escrowed to the intermediary,the payment service providers cannot obtain off-chain transactions information or steal funds.The users can terminate payments with the intermediary at any time,and the user will not loss funds even when the SGX fails.The evaluation shows that this scheme can greatly reduce the payment time and improve the transaction throughputs.