基于区块链的公平可验证的多关键词密文排序检索

针对区块链环境下已有的可搜索加密方案实现结果验证和公平支付的成本过高、检索功能局限的问题，提出基于区块链的支持验证与公平支付的多关键词排序检索方案。该方案通过云服务器（CSP）存储加密索引树和执行搜索操作，并且构建了包含验证证明的查找表来辅助智能合约完成检索结果的验证以及公平支付，从而降低智能合约执行操作的复杂性，节约时间和费用成本。此外，结合向量空间模型与词频逆文档频率（TF-IDF）技术构建平衡二叉树结构的索引，并使用安全K邻近对索引和查询向量进行加密，从而实现支持动态更新的多关键词排序检索。安全性和性能分析表明，所提方案在区块链环境下和已知密文模型下是安全可行的；仿真实验结果表明，所提方案能够以可接受的开销实现结果验证与公平支付。

Fair and verifiable multi-keyword ranked search over encrypted data based on blockchain

In view of the high cost as well as the limitation of retrieval function of the existing searchable encryption schemes based on blockchain to realize result verification and fair payment， a multi-keyword ranked search scheme supporting verification and fair payment was proposed based on blockchain. In the proposed scheme， the Cloud Service Provider （CSP） was used to store the encrypted index tree and perform search operations， and a lookup table including verification certificates was constructed to assist the smart contract to complete the verification of retrieval results and fair payment， which reduced the complexity of smart contract execution and saved time as well as expensive cost. In addition， the index of balanced binary tree structure was constructed by combining vector space model and Term Frequency-Inverse Document Frequency （TF-IDF）， and the index and query vectors were encrypted by using secure K-nearest neighbor， which realized the multi-keyword ranked search supporting dynamic update. Security and performance analysis show that the proposed scheme is secure and feasible in the blockchain environment and under the known ciphertext model. Simulation results show that the proposed scheme can achieve result verification and fair payment with acceptable cost.