支持多用户的高效前向安全可搜索加密方案

大多数已有的前向安全可搜索加密方案主要针对单用户环境，本地存储的关键词状态使得这些方案无法有效拓展到多用户环境；同时支持多用户检索的前向安全方案较少，且需要增设可信的代理服务器，带来了额外的开销，实用性不足。针对目前缺乏实用的多用户前向安全可搜索加密方案的问题，基于一个双链索引结构，设计了满足前向安全和支持多用户检索且无需增设代理服务器的可搜索加密方案(EMFS)。该方案中，双层索引结构由主链索引和侧链索引组成，其中主链索引由陷门单向函数和全局状态生成，不依赖于各个关键词的单独状态，从而避免了关键词状态在多用户间的同步问题；侧链索引采用流密码的方式生成，提高了搜索效率。并将EMFS方案与3个现有的单用户前向安全方案(Sophos、FAST、BESTIE)进行对比实验，实验结果表明EMFS方案有良好的拓展性和实用性:(1)EMFS方案以合理的搜索性能代价实现了支持多用户检索的拓展；(2)EMFS方案尤其适合匹配文件数较大的数据集；(3)EMFS方案具有客户端存储开销小的优势。

Efficient Forward Secure Searchable Symmetric Encryption for Multi-user

Most of the existing forward secure searchable encryption schemes are mainly for single-user settings and cannot be easily extended to multi-user settings since the keyword state is maintained locally; there are few forward secure schemes that support multi-user retrieval, and they require additional trusted proxy servers, which brings additional overhead and insufficient practicality. Aiming at the current lack of practical multi-user forward secure searchable encryption scheme, a searchable encryption scheme (EMFS) based on a two-chain index structure is designed, which meets forward security and supports multi-user retrieval without the need for a proxy server. The double-layer index consists of the main chain index and a slave chain index. The main chain index is generated by the one-way trapdoor function and the global state and does not depend on the separate state of each keyword, thus avoiding the synchronization problem of the keyword state among multiple users; the slave chain index is generated by stream cipher, which improves the search efficiency. Compared with three existing single-user forward security schemes (Sophos, FAST, BESTIE), the results show that the EMFS scheme has good scalability and practicability: (1) The EMFS scheme achieves the expansion of multi-user retrieval at a reasonable cost of search perfor-mance; (2) The EMFS scheme is especially suitable for matching datasets with a large number of files; (3) The EMFS scheme has the advantage of small client storage overhead.