Cryptology ePrint Archive: BibTeX Citation of Report 2011/426

@misc{cryptoeprint:2011:426,
    author = {Masoumeh Safkhani  and  Nasour Bagheri and  Somitra Kumar Sanadhya and Majid Naderi},
    title = {Cryptanalysis of improved Yeh \textit{et al. }'s authentication Protocol: An EPC Class-1 Generation-2 standard compliant protocol},
    howpublished = {Cryptology ePrint Archive, Report 2011/426},
    year = {2011},
    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.