Cryptology ePrint Archive: BibTeX Citation of Report 2003/012

@misc{cryptoeprint:2003:012,
    author = {Marina Pudovkina},
    title = {The number of initial states of the RC4 cipher with the same cycle structure },
    howpublished = {Cryptology ePrint Archive, Report 2003/012},
    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.