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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.