Cryptology ePrint Archive: BibTeX Citation of Report 2004/081

@misc{cryptoeprint:2004:081,
    author = {Philip Hawkes and Gregory G. Rose},
    title = {Rewriting Variables: the Complexity of Fast Algebraic Attacks on Stream Ciphers},
    howpublished = {Cryptology ePrint Archive, Report 2004/081},
    year = {2004},
    note = {\url{http://eprint.iacr.org/}},
}

You will need the url.sty package (comes with most LaTeX installations) for the last line. Otherwise, remove the \url command.