Enhancing the Consensus Fairness Towards Secure Blockchains

PhD Thesis Proposal Defence


Title: "Enhancing the Consensus Fairness Towards Secure Blockchains"

by

Mr. Weijie SUN


Abstract:

Blockchain systems have attracted much attention for allowing mutually 
untrusted nodes to reach agreement without a central authority. The security 
guarantee of such trustless decentralized paradigm largely hinges on 
incentive-compatible consensus protocols, which motivates participants to 
contribute resources and act honestly in exchange for fair rewards. However, 
this foundation of fairness is fragile: adversarial participants may 
misbehave for extra rewards by exploiting protocol flaws, thereby threatening 
both liveness and security. This thesis proposal tackles these 
vulnerabilities by rigorously analyzing consensus fairness and proposing 
practical countermeasures against malicious behavior in both Proof-of-Work 
and Proof-of-Stake blockchains.

First, in Proof-of-Work (PoW) systems, we tackle the selfish mining attack, 
where miners strategically conceal and reveal newly mined blocks to cause 
forks wasting honest computing power and earn unfairly high revenue. To 
address this, we first introduce the unfairness measurement based on the 
KL-divergence from the computing power distribution to the revenue 
distribution of miners. Then we propose a novel block promotion strategy 
called Tit-for-Tat (TFT) for honest miners detecting selfish behavior based 
on fork observations and then selectively delaying block promotions to 
suspicious nodes. To determine the optimal withholding time, we formulate the 
Delay Vector (DV) problem to minimize the attacker's unfair profit and 
propose efficient approximation algorithms to solve it. Extensive experiments 
show that the TFT strategy effectively improves overall system fairness.

Second, in Byzantine Fault Tolerant Proof-of-Stake (BFT-PoS) systems, we 
address the block withholding attack for unfair rewards that yields higher 
latency variability. While BFT-PoS is designed with stable block generation 
intervals, malicious participants can deliberately delay their block 
proposals to capture extra Maximal Extractable Value (MEV) from upcoming 
transactions. To handle this, we introduce InTime to economically motivate 
timely proposals. InTime features an Arrival Rate Incentive (ARI), which 
allocates transaction tips at a finer granularity based on their arrival 
rates across the network, removing the financial benefit of delaying a block.  
To robustly collect and verify these arrival times in a malicious 
environment, we designed the Committee Time Witness (CTW) workflow and a 
Shift-Mean Estimation (SME) algorithm. Our evaluation demonstrates that 
InTime effectively reduces latency variability.

This proposal outlines a detailed research path to addressing consensus 
fairness, a cornerstone of blockchain security. Moreover, we discuss 
potential directions for future work, further securing blockchain systems for 
prevalent data management applications.


Date:                   Monday, 30 June 2025

Time:                   4:00pm - 6:00pm

Venue:                  Room 3494
                        Lifts 25/26

Committee Members:      Prof. Lei Chen (Supervisor)
                        Prof. Qiong Luo (Chairperson)
                        Prof. Qian Zhang