vChain: Enabling Verifiable Boolean Range Queries over Blockchain Databases (1812.02386v1)

Abstract: Blockchains have recently been under the spotlight due to the boom of cryptocurrencies and decentralized applications. There is an increasing demand for querying the data stored in a blockchain database. To ensure query integrity, the user can maintain the entire blockchain database and query the data locally. However, this approach is not economic, if not infeasible, because of the blockchain's huge data size and considerable maintenance costs. In this paper, we take the first step toward investigating the problem of verifiable query processing over blockchain databases. We propose a novel framework, called vChain, that alleviates the storage and computing costs of the user and employs verifiable queries to guarantee the results' integrity. To support verifiable Boolean range queries, we propose an accumulator-based authenticated data structure that enables dynamic aggregation over arbitrary query attributes. Two new indexes are further developed to aggregate intra-block and inter-block data records for efficient query verification. We also propose an inverted prefix tree structure to accelerate the processing of a large number of subscription queries simultaneously. Security analysis and empirical study validate the robustness and practicality of the proposed techniques.

• The paper introduces vChain, a framework enabling verifiable Boolean range queries over blockchain databases without requiring users to maintain full node replicas.
• vChain utilizes a novel accumulator-based authenticated data structure and specialized intra-block and inter-block indexes to ensure efficient query verification and reduce computational load.
• Numerical results show vChain significantly lowers computational cost for both service providers and users while guaranteeing query result integrity, paving the way for lighter blockchain data management.

Overview of vChain: Enabling Verifiable Boolean Range Queries over Blockchain Databases

The paper introduces vChain, a robust framework designed to facilitate verifiable query processing over blockchain databases, addressing issues of data integrity in such environments. Recognizing the limitations of requiring users to maintain full blockchain replicas, vChain offers a solution that empowers users to verify query results while maintaining lightweight client requirements.

vChain operates by utilizing an accumulator-based authenticated data structure (ADS), which allows efficient and verifiable Boolean range queries across blockchain records. This approach is engineered to alleviate the heavy storage and computational demands typically placed on blockchain users, while still ensuring the integrity of the results returned by the queries. The paper delineates three primary contributions: an accumulator-based ADS scheme, a set of new indexes (both intra-block and inter-block), and an inverted prefix tree structure designed to accelerate subscription query processing.

Key Contributions

1. Authenticated Data Structures (ADS):
   • The vChain framework introduces a novel accumulator-based ADS, which underpins the system's ability to handle queries involving both numerical and set-valued attributes. By leveraging accumulators, it effectively maintains a constant-size proof despite an object's attribute set size, ensuring dynamic aggregation possibilities over multi-dimensional and set-valued data.
2. Index Structures for Efficient Query Processing:
   • vChain advances the performance of verifiable queries by implementing both intra-block and inter-block index structures. The intra-block index organizes data within blocks to maximize the efficiency of mismatch pruning, reducing the number of irrelevant proofs the system must verify. In contrast, the inter-block index employs a skip list mechanism that spans across blocks, speeding up query verification by employing batch proofs when multiple blocks do not contain matching data.
3. Scalable Subscription Queries via Inverted Prefix Tree:
   • For scalable management of subscription queries, the paper proposes an inverted prefix tree (IP-Tree) structure. This tree-like architecture organizes subscription queries to enhance the identification of common disjoint conditions over shared data properties, significantly reducing computational redundancy and verification costs.

Numerical Results and Insights

Empirical analysis demonstrates that vChain consistently reduces the computational load for both the service provider (SP) and the end user. For instance, the introduction of ATS reduced computational time for join query operations by more than half in various scenarios, illustrating not only superior performance but also guaranteeing query result integrity. Moreover, the use of accumulators proves essential for enabling efficient batch verification, contributing to lower bandwidth usage by minimizing the size of verification objects (VOs).

Implications and Future Work

vChain represents a significant advancement for blockchain data integrity, particularly in situations where users are unable or unwilling to manage full blockchain nodes. The success of this approach lays a foundation for further exploration into authenticated data structures tailored for distributed and verifiable data storage. The theoretical implications suggest prospective developments in privacy-preserving query systems on blockchain infrastructures, where such verification guarantees might broaden to more complex query types and varied blockchain consensus protocols.

Moving forward, extending vChain to accommodate more sophisticated analytical queries and optimizing its performance on multi-core and distributed architectures could enhance its applicability. Furthermore, leveraging secure hardware extensions and exploring alternative cryptographic primitives could further fortify the framework’s security guarantees. These trajectories offer promising avenues to bolster the usability and security of blockchain data management systems in diverse computational environments.