In recent years, with the popularity of cloud services and the increasing demand for data security protection, dynamic searchable symmetric encryption (DSSE) has attracted widespread attention from academia due to its ability to update and query in encrypted databases. Due to considerations of search and update efficiency, DSSE often needs to disclose some information, mainly search pattern, access pattern, and size pattern. At present, the main use of oblivious random access machine (ORAM) is to protect search and access pattern, but ORAM cannot guarantee the security of size pattern leakage. The article explained the harm of size pattern leakage to security and extended the existing DSSE privacy concept to achieve protection of size patterns, namely proposing strong forward backward privacy. Based on this enhanced security objective, the article proposed an efficient searchable symmetric encryption scheme for size pattern protection named Eurus, aiming to solve the size pattern leakage problem in existing solutions. By combining multi-server ORAM architecture, update slot mechanism and fine tree path elimination technology, Eurus provided strong forward and reversed privacy protection to prevent the disclosure of sensitive keywords and file information. Multi-server ORAM hided search and access patterns, update slots confuse file identifiers, and fine tree path elimination techniques disrupted the actual order of files. The experimental results show that Eurus improves the search and update efficiency while maintaining privacy, improving the search performance by about 46% compared with the existing scheme, and improving the update performance by 4.73 times.
