veffChain: Enabling Freshness Authentication of Rich Queries over Blockchain Databases

With the wide adoption of blockchains in data-intensive applications, enabling verifiable queries over a blockchain database is urgently required. Aiming at reducing costs, previous solutions embed a small-sized authenticated data structure (ADS) in each block header, so that a user can verify search results without maintaining a full copy of blockchain databases. However, existing studies focus on exact queries with difficulty to guarantee the freshness of search results. In this paper, we propose two frameworks, called ${\sf veffChain}$ and ${\sf veffChain++}$ , to realize freshness authentication of rich queries over blockchain databases. Specifically, ${\sf veffChain}$ concerns about verifiable latest- $K$ exact queries and employs RSA accumulator to generate constant-size ADSs; ${\sf veffChain++}$ integrates RSA accumulator into the Trie tree to further authenticate latest- $K$ fuzzy queries. For improved scalability, an adaptive keyword splitting (AKS) solution is proposed to enable ADSs to be incrementally updated. Compared with the state-of-the-art work, our frameworks have the following merits: (1) Freshness Guarantee . The user can efficiently retrieve the freshest data from a blockchain database in a verifiable way. (2) Flexibility . The user can specify different query patterns on demand to retrieve data as accurately as possible. The detailed security analysis and extensive experiments validate the practicality of our frameworks.