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As storage-outsourcing services and resource-sharing networks have become popular, the problem of efficiently proving the integrity of data stored at untrusted servers has received increased attention. In the Provable Data Possession (PDP) model, the client preprocesses the data and then sends them to an untrusted server for storage while keeping a small amount of meta-data. The client later asks the server to prove that the stored data have not been tampered with or deleted (without downloading the actual data). However, existing PDP schemes apply only to static (or append-only) files. We present a definitional framework and efficient constructions for Dynamic Provable Data Possession (DPDP), which extends the PDP model to support provable updates to stored data. We use a new version of authenticated dictionaries based on rank information. The price of dynamic updates is a performance change from O …