Cloud storage service provider, such as dropbox, let users accessing their data over the network without being limited in certain district. At first we upload our data onto the cloud. When we need the data, we download from the cloud and then notice the data is ruined. Thus, it is convenient for supporting a integrity-checking protocol without retrieving the entire data. In this thesis, we proposed an integrity-checking protocol without retrieving the entire file. This protocol is less time consuming in verification time, enabling public verification, and allowing the modification operation. On the other side, we also notice an attack, Changeling attack, that the service provider might be a chance to forge the integrity. Here, we also have the corresponding countermeasures.