@misc{cryptoeprint:2011:139,
author = {Mingjie Liu and Xiaoyun Wang and Guangwu Xu and Xuexin Zheng},
title = {Shortest Lattice Vectors in the Presence of Gaps},
howpublished = {Cryptology ePrint Archive, Report 2011/139},
year = {2011},
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.