Peer-To-Peer-systems (P2P) introduced new methods to distribute large amounts of data to end users. To increase the distribution speed resources from all participating network nodes, the peers, are used, and therefore the workload on own resources decreases. To utilize all peers large data is split into small pieces, so called chunks, and these chunks are distributed among peers therefore making each chunk available on different peers. To identify and find chunks in P2P-systems hash algorithms are used, and each peer is responsible for a specific range of the hash's keyspace and all chunks that fall within this keyspace. With data stored on multiple peers new security risks in terms of confidentiality, integrity, and availability arise. Our security pattern targeted specifically for P2P-systems helps system designers to identify possible threats and show appropriate countermeasures. We show how secure hash algorithms can guarantee the integrity of the distributed data even though chunks are sent to, received from, and stored by multiple, possible untrustworthy, peers.