Lei Xu

CoC: A Unified Distributed Ledger Based Supply Chain Management System

Modern supply chain is a complex system and plays an important role for different sectors under the globalization economic integration background. Supply chain management system is proposed to handle the increasing complexity and improve the efficiency of flows of goods. It is also useful to prevent potential frauds and guarantee trade compliance. Currently, most companies maintain their own IT systems for supply chain management. However, it is hard for these isolated systems to work together and provide a global view of the status of the highly distributed supply chain system. Using emerging decentralized ledger/blockchain technology, which is a special type of distributed system in essence, to build supply chain management system is a promising direction to go. Decentralized ledger usually suffers from low performance and lack of capability to protect information stored on the ledger. To overcome these challenges, we propose CoC (supply chain on blockchain), a novel supply chain management system based on a hybrid decentralized ledger with a novel two-step block construction mechanism. We also design an efficient storage scheme and information protection method that satisfy requirements of supply chain management. These techniques can also be applied to other decentralized ledger based applications with requirements similar to supply chain management.

Decentralized Execution of Smart Contracts: Agent Model Perspective and Its Implications

Smart contracts are one of the most important applications of the blockchain. Most existing smart contract systems assume that for executing contract over a network of decentralized nodes, the outcome in accordance with the majority can be trusted. However, we observe that users involved with a smart contract may strategically take actions to manipulate execution of the contract for purpose to increase their own benefits. We propose an agent model, as the underpinning mechanism for contract execution over a network of decentralized nodes and public ledger, to address this problem and discuss the possibility of preventing users from manipulating smart contract execution by applying principles of game theory and agent based analysis.

Blockchain-based Identity Management with Mobile Device

Blockchain is a powerful and distributed platform for transactions which require a unified, resilient, transparent and consensus-based record keeping system. It has been applied to scenarios like smart city, supply chain, medical data storing and sharing, and etc. Many works have been done on improving the performance and security of such systems. However, there is a lack of the mechanism of identity binding when a human being is involved in corresponding physical world, i.e., if one is involved in an activity, his/her identity in the real world should be correctly reflected in the blockchain system. To mitigate this gap, we propose BlockID, a novel framework for people identity management that leverages biometric authentication and trusted computing technology. We also develop a prototype to demonstrate its feasibility in practice.

Tyranny of the Majority: On the (Im)possibility of Correctness of Smart Contracts

Many consensus protocols are based on the assumption that participants are either “good” or “bad” but ignore the fact that they may be affected by direct or indirect economic interests involved in the corresponding smart contracts. We analyze consensus in decentralized environments and demonstrate that the system cannot guarantee correct execution results.

Proving Conditional Termination for Smart Contracts

Termination of smart contracts is crucial for any blockchain systems security and consistency, especially for those supporting Turing-complete smart contract languages. Resource-constrained blockchain systems, like Ethereum and Hyperledger Fabric, could prevent smart contracts from terminating properly when the pre-allocated resources are not sufficient. The Zen system utilizes the dependent type system of the programming language F* to prove the termination of smart contracts for all inputs during compilation time. Since the smart contract execution usually depends on the current blockchain state and user inputs, this approach is not always successful. In this work, we propose a lazy approach by statically proving conditional termination and non-termination of a smart contract to determine input conditions under which the contract terminates or not. Prior to the execution of the smart contract, the proof-carrying blockchain system will check that its current state and the contracts input satisfy the termination conditions in order to determine if the contract is qualified (i.e., eventually terminating) to run on the chain.

Efficient Public Blockchain Client for Lightweight Users

Public blockchains provide a decentralized method for storing transaction data and have many applications in different sectors. In order for users to track transactions, a simple method is to let them keep a local copy of the entire public ledger. Since the size of the ledger keeps growing, this method becomes increasingly less practical, especially for lightweight users such as IoT devices and smartphones. In order to cope with the problem, several solutions have been proposed to reduce the storage burden. However, existing solutions either achieve a limited storage reduction (e.g., simple payment verification), or rely on some strong security assumption (e.g., the use of trusted server). In this paper, we propose a new approach to solving the problem. Specifically, we propose an underline{e}fficient verification protocol for underline{p}ublic underline{b}lockunderline{c}hains, or EPBC for short. EPBC is particularly suitable for lightweight users, who only need to store a small amount of data that is {it independent of} the size of the blockchain. We analyze EPBCs performance and security, and discuss its integration with existing public ledger systems. Experimental results confirm that EPBC is practical for lightweight users.

EPBC: E fficient P ublic B lockchain C lient for lightweight users

Public blockchains provide a decentralized method for storing transaction data and have many applications in different sectors. In order for a user to track transactions, a simple method is that every user keeps a local copy of the entire public ledger. Since the size of a ledger keeps growing, this method becomes increasingly less practical, especially for lightweight users such as IoT devices and smartphones. In order to deal with this problem, there have been some proposals. However, existing solutions either achieve a limited storage reduction (e.g., simple payment verification), or rely on some strong security assumption (e.g., the use of trusted server). We propose EPBC, a novel and efficient transaction verification scheme for public ledgers, which only requires lightweight users to store a small amount of data that is independent of the size of the blockchain. We analyze EPBCs performance and security, and discuss its integration with existing public ledger systems. Experimental results confirm that EPBC is practical for lightweight users.