@misc{cryptoeprint:2014:680,
author = {Zhengjun Cao and Lihua Liu},
title = {Remarks on the Cryptographic Primitive of Attribute-based Encryption},
howpublished = {Cryptology ePrint Archive, Report 2014/680},
year = {2014},
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.