Secure execution of collaborative processes

So far the number of users on the social network sites has been increasing year-on-year. In the meanwhile, the price of mobile devices drops vertically. Both events push up vigorously the quantity of social users who use mobile devices. This results in a need for collaboration among mobile social users to attain the common goals. The fact that the huge number of users goes online lifts forcefully up the number of services over the Internet. The user requirements for services then get more complex. As a consequence, responding such a complex service request needs a composition of several single services. However, the collaboration among several participants can make the personal data disclosed to the other sides during the collaborative process. Despite the fact that all participants comply with the common protocol and agree on contributing their personal data, they do not trust adequately in each other. This leads to the requirement of preserving user privacy and securing the user data against the other sides. In this dissertation, we investigate different collaboration and participant types. More specifically, they are centralized and decentralized models among users/services. We also concern the communication environment, e.g., mobile network, Internet, or mobile ad-hoc network. The protocols that are enforced in a mobile network environment have more rigorous constraints due to limited physical and performance resources. For preserving user privacy and data security, we study and select different rational and effective cryptography algorithms then apply them into the collaborative protocols. For more understanding, we propose several collaboration scenarios and present them in detail in the upcoming chapters. Each scenario describes a combination of different collaborative type, participant type and network environment. For each scenario, we address issues on privacy preserving and data security and propose selective solutions. In addition, we propose methods for improving network performance. The experimental results show that our proposals are efficient and effective.