Martin Franz, Peter Williams, Bogdan Carbunar, Stefan Katzenbeisser,
Andreas Peter, Radu Sion and Miroslava Sotakova. Oblivious Outsourced
Storage with Delegation. Financial Crypto 2011.

In the past few years, outsourcing private data to untrusted servers
has become an important challenge. This raises severe questions
concerning the security and privacy of the data on the external
storage. In this paper we consider a scenario where multiple clients
want to share data on a server, while hiding all access patterns. We
propose here a first solution to this problem based on Oblivious RAM
(ORAM) techniques. Data owners can delegate rights to external new
clients enabling them to privately access portions of the outsourced
data served by a curious server. Our solution is as efficient as the
underlying ORAM constructs and allows for delegated read or write
access while ensuring strong guarantees for the privacy of the
outsourced data. The server does not learn anything about client
access patterns while clients do not learn anything more than what
their delegated rights permit.