Cryptology ePrint Archive: BibTeX Citation of Report 2013/663

@misc{cryptoeprint:2013:663,
    author = {Javad Alizadeh, Nasour Bagheri, Praveen Gauravaram, Abhishek Kumar, and Somitra Kumar Sanadhya},
    title = {Linear Cryptanalysis of Round Reduced SIMON},
    howpublished = {Cryptology ePrint Archive, Report 2013/663},
    year = {2013},
    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.