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Permutation cipher scheme for verifiable P2P chunk exchange

Peer-to-Peer (P2P) content distribution networks such as BitTorrent swarms, are very popular on Internet. These networks rely on reciprocative chunk contribution of participating peers. However, such reciprocation induces the free-riding behavior, where peers receive chunks from other peers and do not upload chunks in return. It is shown in the literature that tit-for-tat mechanisms within the BitTorrent protocol cannot discourage the free-riding behavior effectively. This paper proposes a permutation cipher scheme for encrypting the chunks to be uploaded. In essence, this scheme splits the entropy of the original chunk into ciphertext entropy part and verification entropy part. The two parts correspond to costs of decrypting cipher chunks and faking cipher chunks, respectively. Through a proper value choice of the unique scheme parameter, the splitting on entropy can be agilely biased towards ciphertext entropy part or verification entropy part with respect to the dynamics of free-riding behavior occurrences in BitTorrent-like content distribution networks.