Keyword-Based Delegable Proofs of Storage.

Cloud users (clients) with limited storage capacity at their end canoutsource bulk data to the cloud storage server. A client can later access herdata by downloading the required data files. However, a large fraction of thedata files the client outsources to the server is often archival in nature thatthe client uses for backup purposes and accesses less frequently. An untrustedserver can thus delete some of these archival data files in order to save somespace (and allocate the same to other clients) without being detected by theclient (data owner). Proofs of storage enable the client to audit her datafiles uploaded to the server in order to ensure the integrity of those files.In this work, we introduce one type of (selective) proofs of storage that wecall keyword-based delegable proofs of storage, where the client wants to auditall her data files containing a specific keyword (e.g., "important"). Moreover,it satisfies the notion of public verifiability where the client can delegatethe auditing task to a third-party auditor who audits the set of filescorresponding to the keyword on behalf of the client. We formally define thesecurity of a keyword-based delegable proof-of-storage protocol. We constructsuch a protocol based on an existing proof-of-storage scheme and analyze thesecurity of our protocol. We argue that the techniques we use can be appliedatop any existing publicly verifiable proof-of-storage scheme for static data.Finally, we discuss the efficiency of our construction.