Piece Fingerprinting: Binding Content and Data Blocks Together in Peer-to-Peer Networks

Peer-to-peer systems provide a scalable content distribution environment where each peer contributes with a share of resources in the distributed system. The efficiency of peer-to-peer networks comes from the file segmentation procedure, allowing peers to redistribute small pieces of the original file as soon as they finish downloading them instead of waiting for the complete file download. Moreover, the decentralized fashion of the paradigm with multiple sources makes it scalable and robust under high churn. Due to the popularity of such systems, many attacks such as content pollution arose, targeting the content integrity by inserting bogus data in the network to increase the download time and bandwidth consumption. In this paper we present the piece fingerprinting mechanism, a new integrity verification procedure that algorithmically binds all pieces together and relates them to the complete file. Each data block resulted from the segmentation of a large file has a fingerprint indicating whether a block belongs to the content file and also allows the integrity verification of specific parts of the content. The mechanism allows the early detection and correction of the corrupted blocks only, reducing the download time and bandwidth consumption which would be spent re-downloading larger pieces. The analytical evaluation shows that the fingerprinting mechanism has low overhead, usually less than 1% of the file size, and can reduce the bandwidth consumption by 90% in the best case by saving the amount of bandwidth consumed from the re- downloaded pieces.