Cryptology ePrint Archive: BibTeX Citation of Report 2012/666

@misc{cryptoeprint:2012:666,
    author = {Chenglian Liu and Ziwei Ye},
    title = {Estimating the Φ(n) of Upper/Lower Bound in its RSA Cryptosystem},
    howpublished = {Cryptology ePrint Archive, Report 2012/666},
    year = {2012},
    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.