In this paper we are interested in privacy preserving discretionary access control (DAC) for outsourced storage such as increasingly popular cloud storage services. Our main goal is to enable clients, who outsource data items, to delegate permissions (read, write, delete) to other clients such that clients are able to unlinkably and anonymously perform operations on outsourced data items when holding adequate permission. In contrast to recent approaches based on oblivious RAM, oblivious transfer combined with anonymous credentials or attribute based encryption, we propose a solution based on dynamic accumulators. In doing so, our approach naturally reflects the concept of access control lists (ACLs), which are a popular means to implement DAC.
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