@misc{cryptoeprint:2015:084,
author = {Zhengjun Cao and Lihua Liu},
title = {On the Disadvantages of Pairing-based Cryptography},
howpublished = {Cryptology ePrint Archive, Report 2015/084},
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.