Abstract
In recent years, due to rapid advancement in network and computer technologies, cloud services have been gradually developed. Among all cloud services, online storage or cloud storage attracts a lot of attention. Many companies, such as Dropbox, Google and etc. have started offering cloud storage services. Being able to access our data from anywhere and at any time, the convenience offered by cloud storage services has fundamentally changed our daily lives. However, the cloud storage services offered by commercial companies in their current form have two drawbacks. First, to use the cloud storage service conveniently offered by a specific cloud storage service provider, users have to install a synchronization program offered by the service provider in their local hosts. This synchronization program keeps the files in the local host synchronized with their remote copies in the cloud. The synchronization programs inevitably allow only one cloud storage service account in each local host. This limits the storage space that users can use. The second drawback of the current cloud storage services is security concern. Although all companies offering cloud storage services claim that users' files are securely encrypted and that maintaining users' privacy has the top priority, most users still worry since the companies also hold the decryption keys. In this thesis we present an architecture to address the two drawbacks described above. In our architecture locally files are maintained in a file tree and remotely our architecture distributes files in multiple cloud storage accounts, such that no account violates its space limit. In our architecture files are encrypted before they are stored in cloud storage accounts. Only users have the decryption keys. In this thesis we also present a prototype implementation of the architecture.