Verifiable re-encryption Scheme in BitTorrent-like cipherblock exchange protocols

BitTorrent-like networks have attracted many Internet peers to cooperatively download media files of large sizes. Yet some selfish peers intentionally constrain their upload bandwidth, exhibiting the free-riding behavior. In response, cipherblock exchange protocols among participating peers have been proposed. The resultant cipherblocks induce big latency with respect to the availability of original blocks of media files. This paper presents a verifiable re-encryption scheme in BitTorrent-like cipherblock exchange protocols. This scheme encrypts bit strings via only bitwise combination operations. As a result, numbers of zero and one bits in the original bit string are unchanged in the resultant bit string, which allows verification checks done by the receiving peers. When re-encrypting the resultant bit string again with combination operations only, the numbers of zero and one bits are still unchanged. Such feature can be leveraged to improve the availability of cipherblocks in cipherblock exchange protocols, and would upgrade download performance, especially for newly arriving peers.