Cryptology ePrint Archive: BibTeX Citation of Report 2007/397

@misc{cryptoeprint:2007:397,
    author = {Chengqing Li, Shujun Li, Muhammad Asim, Juana Nunez, Gonzalo Alvarez and Guanrong Chen},
    title = {On the security defects of an image encryption scheme},
    howpublished = {Cryptology ePrint Archive, Report 2007/397},
    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.