THESIS
2023
1 online resource (xiii, 138 pages) : illustrations (chiefly color)
Abstract
Blockchain technology has attracted significant attention in academia and industry for
establishing trust among participants without a centralized third party, even in the presence
of malicious nodes. However, current blockchain systems still face scalability and
privacy issues which bring limitations in decentralized applications (DApps), hindering
wider adoption. In this thesis, we aim to address the blockchain scalability and privacy
issues, along with enhancing DApp performance through the following detailed 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. To address the ever-growing storage requirement restricting the system
scalabili...[
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Blockchain technology has attracted significant attention in academia and industry for
establishing trust among participants without a centralized third party, even in the presence
of malicious nodes. However, current blockchain systems still face scalability and
privacy issues which bring limitations in decentralized applications (DApps), hindering
wider adoption. In this thesis, we aim to address the blockchain scalability and privacy
issues, along with enhancing DApp performance through the following detailed 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. To address the ever-growing storage requirement restricting the system
scalability, we introduce Consensus Unit (CU) to organize nodes to store at least one
copy of blockchain data together. We optimize the block storage scheme to fully utilize
the storage space with minimized query cost for each node. Meanwhile, we present solutions
to address dynamic scenarios when new blocks arrive and nodes join or depart
from the CU. Extensive experiments confirm the superiority of CU in saving storage and
maintaining the system throughput.
Aspect 2: Transparent records are crucial for public verifiability of blockchain transactions,
but compromise user privacy. Zero-knowledge (set membership) proof (ZKP)
enables private transaction attestation, but existing mechanisms lack scalability. Frequent
addition/removal of set elements incurs significant costs and impacts efficiency, such as
proof generation and verification time. We use sharding techniques to enhance on-chain
state management, employing element-set assignment algorithms for both element addition
and removal cases, minimizing information leakage of frequently used elements. Our
solution is implemented on both Merkle tree and RSA-based state sets to demonstrate its
efficiency and effectiveness.
Aspect 3: Finally, we introduce an innovative blockchain framework that focuses on
optimizing DApp performance with transaction privacy guarantees. We propose L2chain,
a novel blockchain framework that further scales the system by utilizing a layer-2 network
for DApps. The proposed split-execute-merge (SEM) transaction processing workflow,
facilitated by the RSA accumulator, allows DApps to lock and update a part of the state
digest in parallel, enhancing system throughput. We design a witness cache mechanism
for DApp executors to reduce transaction processing latency. To ensure confidentiality, we
leverage the trusted execution environment (TEE) for DApps to execute encrypted transactions
off-chain. To guarantee transaction execution and order correctness, we propose a
two-step execution process for DApps to prevent attacks (i.e., rollback attacks) from subverting
the state transition. Extensive experiments demonstrate that L2chain can achieve
1.5X to 42.2X and 7.1X to 8.9X throughput improvements in permissioned and permissionless
settings respectively.
This thesis provides a detailed roadmap of the problems, solutions, methodologies,
and experimental studies based on relevant datasets and real systems, aiming to design a
new system architecture to achieve a scalable blockchain system with user privacy guarantees
and improved DApp performance.
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