@misc{cryptoeprint:2015:177,
author = {Purushothama B R and Nishat Koti},
title = {On the Security of an Efficient Group Key Agreement Scheme for MANETs},
howpublished = {Cryptology ePrint Archive, Report 2015/177},
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.