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File-Based Network Collaboration System

Toshinari Takahashi, Atsushi Shimbo, and Masao Murota
Communication and Information Systems Research Labs.
1 Komukai-Toshiba-cho, Saiwai-ku, Kawasaki 210 Japan


Computer-Supported Cooperative Work (CSCW) requires coordinated access to shared information over computer networks; such networks have tended to use wires, but wireless networks are now becoming common. There are a large number of tools aimed at helping users to work cooperatively but these tend to be application specific, leading to proliferation and requiring a large amount of development effort. A more general purpose mechanism would keep the number of tools manageable, and would obviate the need to develop a completely new tool for each problem area. Data security is also a very important requirement in distributed systems. A solution to the problems of cooperative working must take this security requirement into account. This paper describes a mechanism aimed at both problems: a general purpose tool for cooperative working that is more secure than existing proposals. Our approach is novel in that we do not require explicit locking, which can lead to a number of problems, particularly in distributed systems, as we shall explain. Client routines act upon user requests to insert or delete blocks in a file, and request a file-server to modify a shared file according to those requests. The file-server receives encrypted requests asynchronously and merges these requests into the current version of the document without decrypting the requests. Indeed, an interesting feature of our proposal is that the server could not decrypt the content of these requests even if it wanted to. We call this mechanism "privacy enhanced merging". Our current implementation includes a concurrent editing application that we call "Network BBS"; the server is able to make use of a conventional file-system. This is an experimental tool of our proposed "Collaborative File System".

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