Blockchain Technology and Application

In the past few years, blockchains have been one of the most attractive emerging technologies. Many researchers and institutions have devoted their resources to the development of more effective blockchain technologies and innovative applications. However, with the limitation of computing power and financial resources, it is hard for researchers to deploy and test their blockchain innovations in a large-scape physical network. In this paper, we design a peer to peer blockchain simulation framework to address this challenge, called ChainSim. ChainSim provides a foundation and skeleton to argument and simulate as large as thousand-nodes P2P blockchain network with a single computer. This paper presents ChainSim basic structure and simulation mechanism; and showcase ChainSim capabilities and usefulness. With ChainSim, researchers can test their new consensus protocols, reproduce a subtle security attack and evaluate its risks with a large number of nodes under heavily transaction loads.

With rapid development of the information age, the proportion of electronic evidence involved in judicial cases has been rising, and the importance of electronic evidence is increasingly prominent. In the real judicial process, there are strict requirements put forward for the authenticity identification, tamper proof storage and legal sharing methods of electronic evidence, bringing many security challenges. If such conditions are not met, the legal force of electronic evidence will be seriously reduced. However, the existing technical solutions can not meet these above requirements. Blockchain technology has the characteristics of decentralization and tamper proof, which provides a new method for the storage and extraction of electronic evidence. To solve these problems, this paper proposes a blockchain-based storage access control model for electronic evidence and designs the corresponding storage access control protocol. In this scheme, multi-entity cooperation is allowed to store evidence, and a zero-knowledge proof protocol is applied to achieve access control and data sharing. Through the security and experimental analysis, it can be proved that the scheme satisfies security features such as known key security and non-repudiation, and can effectively resist collusion, camouflage, replay and man-in-the-middle attacks. Finally, related experiments show that the scheme has high computational and communication efficiency. In this way, the problem of secure storage and sharing of electronic evidence will be resolved commendably, which meets the security requirements in actual scene.

Today’s digital copyright protection system is completely centralized and the confirmation and transaction of copyright depend entirely on a third party, which suffers from time-consumption, high cost and data isolation. In this paper, we propose a secure and efficient digital copyright protection system based on blockchain technology and IPFS that provides a whole process of copyright protection services including confirmation, registration, subscription, buying, tracing and querying. A series of encryption algorithms are adopted to ensure the security of the system and smart contracts are utilized to achieve automatic confirmation and transaction of copyright. Moreover, we present key aspects related to architectural design and interactions details between system components. In order to validate the proposed system, we evaluated the whole system in terms of function, performance and security aspects. Our test and analysis suggest that the proposed system can help to solve the problem caused by the current copyright protection system.

SHA-256 is a completely unpredictable pseudorandom function which generates unique output for a given input ensuring data authenticity and non-repudiation. It is the cornerstone for imparting security and privacy into Blockchain and its efficiency of calculation decides the performance of Blockchain. In this paper, we propose two novel methods to accelerate the calculation of SHA-256 in different situations. To eliminate the useless operations, we present pre-expanded padding blocks and hard coded into the software. On this basis, for a single message containing multiple 512-bit message blocks, we propose Interleaved Multi-Vectorizing Message Scheduling (IMV-MS) to optimize the message schedule stage of SHA-256, which utilize the interleaved multi-vectorizing (IMV) to combine single instruction multiple data (SIMD) vectorization with SHA-256. It splits a vectorized program into multiple states, then it interleaves the execution of vectorized states from those running instances which can make full use of the data parallelism in SIMD. On the other hand, in the situation where we hash several messages simultaneously, we propose the modified SHA-256 which employs SIMD instructions and thread-level parallelism technology together to realize parallel optimization on SHA-256. As experimental results show, IMV-MS and the proposed SHA-256 achieves up to 6.36X, 60.38X better performance compared with the pure SIMD vectorization and the pure scalar implementation, respectively.

The current centralized educational data management system results in problems like malicious tampering, low cost of diploma fabrication, and high cost of certificate verification. The start-of-the-art decentralized blockchain technology can be applied to solve the problems. In this paper, we reveal the shortages of current centralized systems and propose EduChain, a heterogeneous blockchain education data management system, which leverages the advantages of both private blockchains and consortium blockchains. We also propose an effective mechanism to conduct database consistency check and error traceback based on the second consensus via pt-table-checksum tool to solve the database mismatching problem. This system shows good performance in information verification, error traceback and data security.

With product iteration and emerging market demand, traditional organizations have to look for ways to exchange information and trade options/swaps under trust-less network. In this paper, we propose – “BATN”: a prototype for bid and ask trading network based on Blockchain. We propose a system in which a decentralized network of trading agencies, supervisor institutions and witness nodes can enable public bid/ask, automated risk evaluation, and transparent supervision through a trail of historic trading behavior and smart contracts. Our system decentralizes critical information about alliance governance, authentication and credit evaluation through a verifiable audit trail. We present BATN using Hyperchain through which a consortium of geographically dispersed organizations can operate business, sign e-contracts and report transactions anywhere and anytime. Our prototype makes sure the transaction per second on a decentralized network can meet trading volume in reality. This paper intends to improve business effectiveness for much larger fields through the working prototype and discusses the potential of blockchain for finance IT.

Focusing on the problems of high energy consumption, low efficiency and poor scalability of Practical Byzantine Fault Tolerance (PBFT) consensus algorithm existed in consortium blockchain, this paper presents a group-based optimized Practical Byzantine Fault Tolerance (GPBFT) consensus algorithm, which is a multi-stage algorithm. First, we propose a comprehensive reputation evaluation model to judge the credibility of a node from two aspects of transaction behavior and consensus performance. Then, the nodes with higher reputation value will be selected to enter the consensus group, and the other nodes with block packaging ability are selected as candidate nodes. Finally, we optimize the PBFT based on the application scenario of blockchain, change the three stages to two, which reduces the number of messages delivered by 50% at least. The experimental results demonstrate that GPBFT gains better performance. While ensuring the security and reliability of the system, it shows good scalability, thus it can be used in large-scale consortium blockchain system.

In recent years, many researches on decentralized PKI (Public Key Infrastructure) by using block technology have emerged to prevent problems faced by tradition PKI, such as single point of failure. Certificates are recorded into the decentralized blockchain in many of the researches. With the increased number of certificates, the blockchain based PKI system will occupy a considerable amount of storage space. In this paper, the framework of blockchain based PKI system is introduced, and optimizations for certificate storage are provided. The certificates have expiry dates, and the optimization based on the invalid certificates is proposed. In many applications and scenarios, the target certificates are explicit, and then the optimization based on the target certificates is proposed. These optimization methods could improve the storage efficiency of specific nodes in blockchain based PKI system.