File-Based Network Collaboration System
Toshinari Takahashi, Atsushi Shimbo, and Masao Murota
Communication and Information Systems Research Labs.
TOSHIBA R&D Center
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
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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