We explore secure, cooperative storage mechanisms in peer-to-peer networks, where a group of peer nodes form a contributory storage infrastructure. In this collective storage platform, each peer node can access a large pool of information by only contributing a small portion of the total required storage. The basic idea is that we fragment a given data-object into several segments and store them in the peer nodes based on DHT (distributed hash table). Each segment is associated with a partial key, and the master key can be retrieved if the number of assembled partial keys reaches a given threshold. In practice, this means one can enlist one's peer group to help with one's storage needs, and vice versa; it is also secure even when one loses one's password.