@misc{cryptoeprint:2013:218,
author = {Aurore Guillevic},
title = {Comparing the Pairing Efficiency over Composite-Order and Prime-Order Elliptic Curves},
howpublished = {Cryptology ePrint Archive, Report 2013/218},
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.