@misc{cryptoeprint:2015:197,
author = {N. Nalla Anandakumar},
title = {SCA Resistance Analysis on FPGA Implementations of Sponge based MAC-PHOTON},
howpublished = {Cryptology ePrint Archive, Report 2015/197},
year = {2015},
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.