Cryptology ePrint Archive: BibTeX Citation of Report 2003/199

@misc{cryptoeprint:2003:199,
    author = {Simon R. Blackburn and Kenneth G. Paterson},
    title = {Cryptanalysis of a Message Authentication Code due to Cary and Venkatesan},
    howpublished = {Cryptology ePrint Archive, Report 2003/199},
    year = {2003},
    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.