Patent ID: 8909668

Claim:
A system comprising: a distribution server; an ID server; and a plurality of peers connected to a network, wherein the distribution server has a unit calculating feature quantities of contents written in a plurality of files by using a common calculation operation and notifying the ID server of the calculated feature quantities, and a unit implementing a primary distribution by transmitting the plurality of files along with their respective IDs to the peers, the feature quantities being fingerprints or electronic watermarks used for uniquely identifying the contents regardless of formats of the files, the ID server has a unit allotting a common ID to feature quantities which are equivalent to each other among the notified feature quantities from the distribution server and allotting different IDs to feature quantities which are different from each other, and a unit notifying the distribution server of the allotted ID, and each of the plurality of peers has: a unit associating the plurality of files with the IDs transmitted by the primary distribution and storing the associated files and IDs; a unit gathering, when obtaining the file stored in another peer, information on ID of said file and said another peer though the network, by: a unit transferring a request from another peer related to the gathering of the information; a unit requesting the another peer shown in the gathered information to transmit the file corresponding to the ID shown in said information; and a unit transmitting the stored file to another peer when said file is requested by said another peer.