owadays data outsourcing are developing and data owners are motivated to outsource their data to cloud server for great convenience and reduce cost in data management . Despite of owner’s interest to data outsourcing , after storing sensitive information in remote server , they are concern about data privacy . To ensure data confidentiality , encrypting the data before outsourcing it is advised . While encryption protects the secrets in the data , it also prevents operations on the data such as common data retrieval approach for search . Therefore search over encrypted data is a hot research field that called Searchable Encryption . Efficient searchable encryption schemes with multi-keyword , ranked search are proposed , but most of them are limited to single-user setting . Another field of research in Data outsourcing is Access control . Searchable encryption scheme becomes more challenging when users have different access rights in system , which called multi-user system . In a multi-user setting each user allowed to access a part of data that define in access control policy . Due to the fact that the cloud server is not trusted , the user access pattern don’t send to server . Most of the existion scheme are limited to searchable encryption or access control but a practical scheme that search on encrypted data with regarding to user access control that hide from sever is not proposed . To solve the problem of multi-user searchable some scheme have been proposed that most of them are single keyword and access pattern don’t hide from servers . SE scheme are more efficient when the files can be retrieved if the user has access to it . In this thesis , for the first time , we propose a multi-user and multi-keyword searchable encryption scheme which server can understand minimum information about user’s access pattern to documents . We design two schemes for combining searchable encryption and access , one is multi-user and multi-keyword searchable encryption with one server and coarse-grain access control , and the other is multi-user and multi-keyword searchable encryption with tow server and fine-grain access control which hides access control from servers . Security analysis shows that our scheme is secure . Key words: Data Outsourcing, Searchable Encry[tion, Multi-user System, Access Control, Multi- keyword Search, Vector Space Model
