With the rapid development of blockchain, Byzantine fault-tolerant protocols have attracted revived interest recently. To overcome the theoretical bounds of Byzantine fault tolerance, many protocols attempt to use Trusted Execution Environment (TEE) to prevent equivocation and improve fault tolerance from less than 1/3 to minority. However, due to the broken quorum intersection assumption caused by the reduction of replica number, most improvements introduce higher communication complexity or more protocol phases, which affects the performance and scalability of existing TEE-based protocols and prevents them to be applied to large-scale blockchain systems. In this paper, we propose TBFT, an efficient Byzantine fault-tolerant protocol in the partial synchrony setting, which has O(n) message complexity and only two protocol phases in normal-case. The key insight behind TBFT is introducing novel TEE-assisted primitives to limit malicious behaviors of replicas including not only equivocation but also message log forgery and message history forgery, therefore both the communication complexity and protocol phases can be reduced. We have implemented TBFT and evaluated it through systematic analysis and experiments, and the results show that TBFT has better performance and scalability compared to other protocols.

The efficiency of block lifecycle determines the performance of blockchain, which is critically affected by the execution, mining and validation steps in blockchain lifecycle. To accelerate blockchains, many works focus on optimizing the mining step while ignoring other steps. In this paper, we propose a novel blockchain framework-FastBlock to speed up the execution and validation steps by introducing efficient concurrency. To efficiently prevent the potential concurrency violations, FastBlock utilizes symbolic execution to identify minimal atomic sections in each transaction and guarantees the atomicity of these sections in execution step via an efficient concurrency control mechanism-hardware transactional memory (HTM). To enable a deterministic validation step, FastBlock concurrently re-executes transactions based on a happen-before graph without increasing block size. Finally, we implement FastBlock and evaluate it in terms of conflicting transactions rate, number of transactions per block, and varying thread number. Our results indicate that FastBlock is efficient: the execution step and validation step speed up to 3.0x and 2.3x on average over the original serial model respectively with eight concurrent threads.

In recent years, many decentralized applications based on blockchain (DApp) have been developed. Some development tools provide testing functions, but only for developers to write unit tests for smart contracts rather than test DApp as a whole. Moreover, due to the difficulty for testers to understand the implementation details of smart contracts, insufficient functional testing causes some DApps not to meet functional design expectations. The inherent complexity of DApp, inconvenient pre-state setting, and not-so-readable logs make DApp testing challenging. In this paper, we propose Kaya, a testing framework for DApps to bridge these gaps. Firstly, Kaya formulate automatically executed test cases that cover both front-end behaviors and back-end logics with simple setting. Secondly, Kaya provides a flexible and convenient way for test engineers to set the blockchain pre-states. Thirdly, Kaya transforms incomprehensible addresses into readable variables for easier comprehension. Besides, to fit the various application environments, we provide both GUI and CLI for test engineers to use Kaya. Our case study and preliminary human study demonstrates the potential of Kaya in helping test engineers to test DApps more easily. A demo video is at https://youtu.be/7DyI_EpVZFw.

Smart contracts are the back-end programs of blockchain-based applications and the execution results are deterministic and publicly visible. Developers are unwilling to release source code of some smart contracts to generate randomness or for security reasons, however, attackers still can use reverse engineering tools to decompile and analyze the code. In this paper, we propose EShield, an automated security enhancement tool for protecting smart contracts against reverse engineering. EShield replaces original instructions of operating jump addresses with anti-patterns to interfere with control flow recovery from bytecode. We have implemented four methods in EShield and conducted an experiment on over 20k smart contracts. The evaluation results show that all the protected smart contracts are resistant to three different reverse engineering tools with little extra gas cost.

The Tor network is one of the largest anonymity networks and has attracted millions of users worldwide. Since deployed in October 2002, many forms of attacks against Tor had been proposed, aiming to deanonymize the network. The protocol-level attacks, which can deanonymize users by manipulating a cell, are effective to compromise the anonymity of Tor by controlling the entry node and the exit node in a circuit. However, due to the absence of stealthiness, it may be noticed by the victim since the connection will be released. To address this issue, we present two types of attacks. The Type-I is based on protocol-level strategy but attempts to keep the connections alive by fixing damaged cells in the network, thereby making it much stealthier in some cases and it is quite difficult to be defended. In the Type-II attack, the entry node sends a signal to the accomplice exit node via a special type of outbound cells to prevent the connection from being closed, thus the attack can keep stealthy in more general situations. We also propose some countermeasures to keep the network away from the Type- II attack. An evaluation of the two types of attacks has been performed. And the results showed that both the two types of attacks are effective and pose serious threats to the Tor network.