Cryptology ePrint Archive: BibTeX Citation of Report 2002/005

@misc{cryptoeprint:2002:005,
    author = {Hongjun Wu and Feng Bao},
    title = {Cryptanalysis of Stream Cipher COS (2,128) Mode I},
    howpublished = {Cryptology ePrint Archive, Report 2002/005},
    year = {2002},
    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.