@misc{cryptoeprint:2015:529,
author = {Colin O'Flynn and Zhizhang Chen},
title = {Power Analysis Attacks against IEEE 802.15.4 Nodes},
howpublished = {Cryptology ePrint Archive, Report 2015/529},
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.