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Top1. Introduction
With the development of computer technology, more and more data security problems are exposed (Pajany and Zayaraz, 2021). In 2018, network security incidents worldwide had caused a total loss of more than 45 billion US dollars. In 2019, a Philippine financial service company is attacked by hackers, resulting in data leakage. Nearly 900000 users' data are stolen and sold on the network. The reason for this is that database security is not guaranteed. Database audit is an essential technology to ensure data security. It can record all the actions that have operated on the database in real time and analyze these operations. If there is a problem during the audit, it can help maintenance personnel quickly analyze and locate the problem in time, preventing data leakage and protecting data security (von Sanden and Neideck, 2021). With the development of the era of big data, Blockchain Technology (BT) has penetrated into all walks of life and gained much attention in auditing. BT first appeared in the form of Bitcoin. BT is the underlying technology of Bitcoin and was first used in Bitcoin. At present, the research of BT in audit database servers is relatively shallow (Feng & Chen, 2022) (Wang et al., 2020).
Although it can audit users’ information efficiently, the plaintext audit scheme also causes user privacy disclosure. In contrast, the security of the ciphertext audit scheme is more reliable. With the improvement of the theoretical system, searchable encryption’s application to audit work is getting more and more increasing. Jiang et al. (2018) proposed an audit protocol of principal-agent outsourcing data in the scenario of cloud computing. He used the asymmetric encryption algorithm to verify the integrity of data blocks and Hashtable to construct the index for the keyword dictionary of a data set to realize rapid search of keywords (Jiang et al., 2018). Li et al. (2021) proposed the searchable encrypted audit log in cloud storage system. The information to be audited is encrypted and transmitted by the asymmetric searchable encryption algorithm. The client is identified after the cloud service provider verifies the searchable encrypted audit log. This method protects the user's privacy and allows cloud service providers to monitor the behavior of clients in real time (Li et al., 2021). Hao et al. (2021) proposed an audit method based on a knowledge map. As a big data technology, the knowledge map has visualization characteristics and can analyze the relationship between entities. This method improves the audit efficiency, but the internal attack is not addressed in the audit (Hao et al., 2021). Li et al. (2021) put forward a search encryption scheme based on BT (Blockchain Technology). A searchable encryption algorithm based on symmetric encryption builds a distributed storage server. It can solve the problem that the search results of cloud service providers cannot be verified in an untrusted cloud server environment, resulting in incorrect information return (Li et al., 2021).