Cryptology ePrint Archive: BibTeX Citation of Report 2005/103

@misc{cryptoeprint:2005:103,
    author = {Fangguo Zhang and Xiaofeng Chen},
    title = {Cryptanalysis and improvement of an ID-based ad-hoc anonymous identification scheme at CT-RSA 05},
    howpublished = {Cryptology ePrint Archive, Report 2005/103},
    year = {2005},
    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.