@misc{cryptoeprint:2014:738,
author = {N. Nalla Anandakumar and Thomas Peyrin and Axel Poschmann},
title = {A Very Compact FPGA Implementation of LED and PHOTON},
howpublished = {Cryptology ePrint Archive, Report 2014/738},
year = {2014},
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.