@misc{cryptoeprint:2013:855,
author = {Mete Akg\"{u}n, M. Ufuk \c{C}a\v{g}layan},
title = {Weaknesses in a Recently Proposed RFID Authentication Protocol},
howpublished = {Cryptology ePrint Archive, Report 2013/855},
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.