Cryptology ePrint Archive: BibTeX Citation of Report 2007/230

@misc{cryptoeprint:2007:230,
    author = {Gautham Sekar and Souradyuti Paul and Bart Preneel},
    title = {New Weaknesses in the Keystream Generation Algorithms of the Stream Ciphers TPy and Py},
    howpublished = {Cryptology ePrint Archive, Report 2007/230},
    year = {2007},
    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.