Enabling Non-repudiable Data Possession Verification in Cloud Storage Systems

After clients outsource their data to the cloud, they will lose physical control of their data. Many schemes are proposed for clients to verify the integrity of their data. This paper considers a complementary problem: When a client claims that the server has lost their data, how can we be sure that the client is correct and honest about the loss? It is possible that the client's meta data is corrupted or the client is lying in order to blackmail the server. In addition, most previous work relies on sequential indices. However, the indices bring significant overhead to bind an index to each block. We propose to replace sequential indices with much flexible non-sequential {\it coordinates}. The binding of coordinates to data blocks is performed through a Coordinate Merkle Hash Tree (CMHT). Based on CMHT, we can improve both the average and the worst-case update overhead by simplifying the updating algorithm.