In current computing environments, collaborative computing has been a central concern in Ubiquitous, Convergent, and Social Computing. "MobiLife¿ and "MyLifeBits¿ are the leading projects for representing dailylifeservices and their systems require complicate and collaborative network systems. The collaborative computing environments remain in high potential risks for users' security and privacy because of diverse attack routes. In order to solve the problems, we design combined authentication and multilevel access control, which deals with cryptographic methods in a personal database of "MyLifeBits¿ system. We propose a scheme which is flexible in dynamic access authorization changes, secure against all the attacks from various routes, a minimum round of protocol, privacy preserving access control, and multifunctional.

In a real world, it is often in a group setting that sensitive information has to be stored in databases of a server. Although personal information does not need to be stored in a server, the secret information shared by group members is likely to be stored there. The shared sensitive information requires more security and privacy protection. To our best knowledge, there is no paper which deals with applicable group search schemes to a real world over encrypted data. In this paper, we propose two schemes which can search the encrypted documents without re-encrypting all documents in a server even if group keys have to be updated. The schemes can support general database normalization for encrypted database. Our experiments show that our schemes are much more efficient than the existing schemes.