Chen Feng

We present EBFT, an egalitarian framework of BFT consensus for permissioned blockchains. The key innovation in EBFT is egalitarian block generation: instead of relying on a fixed leader, nodes randomly and non-interactively propose blocks, which makes the system resilient to attacks targeting the leader. By combining the longest-chain rule from Nakamoto consensus with quorum voting from classical BFT, EBFT achieves deterministic safety with a design as simple as Nakamoto consensus. To demonstrate its practicality, we build three protocols: EBFT-SYN for synchronous networks, EBFTPSYN for partially synchronous networks, and EBFT-TURBO, a variant that incorporates Bitcoin-NG style decoupling to demonstrate the framework's extensibility towards high performance. We implement EBFT atop the Go version of Bitcoin, btcd. We implemented EBFT-SYN, EBFT-PSYN and EBFT-TURBO in about 920 LoCs in total. This indicates that EBFT can be built on top of existing blockchains with relatively little effort. We evaluate these protocols on EC2 instances with up to 256 nodes. Our evaluation shows that EBFT-SYN (resp. EBFT-PSYN) achieves a latency of 6 (resp 1) seconds. EBFT-TURBO can process up to 3.2k transactions per second and has a latency of 8 seconds.

With the growing popularity of blockchains, modern chained BFT protocols combining chaining and leader rotation to obtain better efficiency and leadership democracy have received increasing interest. Although the efficiency provisions of chained BFT protocols have been thoroughly analyzed, the leadership democracy has received little attention in prior work. In this paper, we scrutinize the leadership democracy of four representative chained BFT protocols, especially under attack. To this end, we propose a unified framework with two evaluation metrics, i.e., chain quality and censorship resilience, and quantitatively analyze chosen protocols through the Markov Decision Process (MDP). With this framework, we further examine the impact of two key components, i.e., voting pattern and leader rotation, on leadership democracy. Our results indicate that leader rotation is not enough to provide the leadership democracy guarantee; an adversary could utilize the design, e.g., voting pattern, to deteriorate the leadership democracy significantly. Based on the analysis results, we propose customized countermeasures for three evaluated protocols to improve their leadership democracy with only slight protocol overhead and no change of consensus rules. We also discuss future directions toward building more democratic chained BFT protocols.

The proliferation of blockchain-backed cryptocurrencies has sparked the need for cross-chain exchanges of diverse digital assets. Unfortunately, current exchanges suffer from high on-chain verification costs, weak threat models of central trusted parties, or synchronous requirements, making them impractical for currency trading applications. In this paper, we present MERCURY, a practical cryptocurrency exchange that is trust-minimized and efficient without online-client requirements. MERCURY leverages Trusted Execution Environments (TEEs) to shield participants from malicious behaviors, eliminating the reliance on trusted participants and making on-chain verification efficient. Despite the simple idea, building a practical TEE-assisted cross-chain exchange is challenging due to the security and unavailability issues of TEEs. MERCURY tackles the unavailability problem of TEEs by implementing an efficient challenge-response mechanism executed on smart contracts. Furthermore, MERCURY utilizes a lightweight transaction verification mechanism and adopts multiple optimizations to reduce on-chain costs. Comparative evaluations with XClaim, ZK-bridge, and Tesseract demonstrate that MERCURY significantly reduces on-chain costs by approximately 67.87%, 45.01%, and 47.70%, respectively.

Rollups have emerged as a promising approach to improving blockchains’ scalability by offloading transaction execution off-chain. Existing rollup solutions either leverage complex zero-knowledge proofs or optimistically assume execution correctness unless challenged. However, these solutions suffer from high gas costs and significant withdrawal delays, hindering their adoption in decentralized applications. This paper introduces TeeRollup, an efficient rollup protocol that leverages Trusted Execution Environments (TEEs) to achieve both low gas costs and short withdrawal delays. Sequencers (i.e., system participants) execute transactions within TEEs and upload signed execution results to the blockchain with confidential keys of TEEs. Unlike most TEE-assisted blockchain designs, TeeRollup adopts a practical threat model where the integrity and availability of TEEs may be compromised. To address these issues, we first introduce a distributed system of sequencers with heterogeneous TEEs, ensuring system security even if a certain proportion of TEEs are compromised. Second, we propose a challenge mechanism to solve the redeemability issue caused by TEE unavailability. Furthermore, TeeRollup incorporates Data Availability Providers (DAPs) to reduce on-chain storage overhead and uses a laziness penalty mechanism to regulate DAP behavior. We implement a prototype of TeeRollup in Golang, using the Ethereum test network, Sepolia. Our experimental results indicate that TeeRollup outperforms zero-knowledge rollups (ZK-rollups), reducing on-chain verification costs by approximately 86% and withdrawal delays to a few minutes.

This paper introduces a novel framework for constructing algebraic lattices based on Construction-D, leveraging nested linear codes and prime ideals from algebraic number fields. We focus on the application of these lattices in block-fading (BF) channels, which are characterized by piecewise-constant fading across blocks of transmitted symbols. This approach results in a semi-systematic generator matrix, providing a structured foundation for high-dimensional lattice design for BF channels. The proposed Construction-D lattices exhibit the full diversity property, making them highly effective for error performance improvement. To address this, we develop an efficient decoding algorithm designed specifically for full-diversity Construction-D lattices. Simulations indicate that the proposed lattices notably enhance error performance compared to full-diversity Construction-A lattices in diversity-2 cases. Interestingly, unlike AWGN channels, the expected performance enhancement of Construction-D over Construction-A, resulting from an increased number of nested code levels, was observed only in the two-level and diversity-2 cases. This phenomenon is likely attributed to the intensified effects of error propagation that occur during successive cancellation at higher levels, as well as the higher diversity orders. These findings highlight the promise of Construction-D lattices as an effective coding strategy for enhancing communication reliability in BF channels.