CapaFS: A globally Accessible File System

Abstract

We have designed and implemented a reference implementation of CapaFS, a global, decentralised file system that allows users to collaborate with other users anywhere in the world, with no prior arrangements or connections. The system uses filenames as sparse capabilities to name and grant access to files on remote servers. Users can share files by exchanging capability filenames with parties that they trust. Possession of a capability filename is the necessary and sufficient proof of authority to perform the operations, authorised by the capability on the file it names. CapaFS does not need to establish trust between client and server, it only needs to verify the validity of the CapaFS capability filename. By using CapaFS we can demonstrate a globally accessable file system with a uniform namespace, that does not need any central authority to manage the namespace. We show that the capability filenames used in CapaFS are a secure and practical solution to sharing resources. We also prove the reference implementation of CapaFS can offer reasonable performance when compared with systems like NFS. The results of CapaFS show that the cost of software encryption can be tolerated in large networks like the Internet, where the cost of encryption is a small percentage of the total delay. CapaFS offers new functionality to users which sucessfully promotes the sharing of files and collaboration on the Internet, without imposing significant costs in terms of overhead and performance.