Abstract-- With fast paced growth of digital data and exploding storage management costs, enterprises are looking for new ways to effectively manage their data. One such cost-effective paradigm is the Storage-as-a-Service model, in which enterprises outsource their storage to a storage service provider (SSP) by storing data at a remote SSP-managed site and accessing it over a high speed network. Often for a variety of reasons, enterprises find it unacceptable to fully trust the SSP and prefer to store data in an encrypted form. This typically limits collaboration and data sharing among enterprise users due to complex key management and access control challenges. In this paper, we propose a platform called SHAROES that provides data sharing capability over such outsourced storage environments. SHAROES provide rich *nix-like data sharing semantics over SSP stored data, without trusting the SSP for data confidentiality or access control. SHAROES is unique in its ability in reducing user i...