On Scalable Blockchain Systems with User Privacy Guarantees

PhD Thesis Proposal Defence


Title: "On Scalable Blockchain Systems with User Privacy Guarantees"

by

Mr. Zihuan XU


Abstract:

Blockchain technology has attracted much attention in both academia and 
industry due to its success in building trust among participants without a 
centralized third party, even with the existence of malicious nodes. 
However, compared to traditional databases, current blockchain systems 
still cannot handle a massive number of transactions to accommodate more 
users (a.k.a., scalability issues). In this thesis, we aim to address the 
blockchain scalability issue from two aspects:

Aspect 1: The original blockchain design requires all participants to keep 
the same copy of all historical data in order to verify newly-generated 
transactions and prevent record tampering. However, the ever-growing 
storage requirement can easily become a barrier to accommodate more users, 
especially for low-end devices such as mobile. To address this challenge, 
we introduce Consensus Unit (CU) to organize nodes to store at least one 
copy of blockchain data together. Moreover, we further optimize the block 
storage scheme to fully utilize the storage space with minimized query 
cost for each node. Meanwhile, we present solutions to address the dynamic 
scenarios when new blocks arrive and nodes join or depart from the CU. To 
verify the effectiveness of CU, we have conducted extensive experiments 
which confirm the superiority of CU in saving storage and maintaining the 
system throughput.

Aspect 2: Transparent records ever are the key to making blockchain 
transactions publicly verifiable. However, it also breaks user privacy. 
Recently, Zero-knowledge (set membership) proof (ZKP) is widely used to 
enable private transaction attestation. However, existing mechanisms do 
not fully consider scalability. Particularly, frequent addition/removal of 
set elements, not only brings the significant cost to keep public 
parameters up to date to provers and verifiers but also affects mechanism 
efficiency (e.g., generation time of the proof and verification, etc.). To 
address this challenge, we leverage the sharding technique to assist the 
on-chain state management with specially designed element-set assignment 
algorithms under both element addition and removal cases to minimize the 
potential information leakage of the frequently used elements. We 
implement our solution on both Merkle tree and RSA-based state sets to 
evaluate its efficiency and effectiveness and use a real ZKP-based 
application named zkSync to demonstrate its applicability. Results show 
that our solution can notably reduce the system latency with a growing 
number of users.

This proposal will provide a detailed research roadmap of the 
aforementioned topics including the formal problem definitions, 
corresponding solutions as well as the methodology of experimental 
studies. Especially, we will discuss related works in scaling blockchain 
systems to motivate our future direction, aiming to design a new system 
architecture to achieve a scalable blockchain system with user privacy 
guarantees.


Date:			Monday, 13 March 2023

Time:                  	12:00noon - 2:00pm

Venue:			Room 4472
  			lifts 25/26

Committee Members:	Prof. Lei Chen (Supervisor)
   			Prof. Bo Li (Chairperson)
 			Dr. Xiaojuan Ma
 			Dr. Yangqiu Song


**** ALL are Welcome ****