@misc{cryptoeprint:2010:137,
author = {Markus Rückert and Michael Schneider},
title = {Estimating the Security of Lattice-based Cryptosystems},
howpublished = {Cryptology ePrint Archive, Report 2010/137},
year = {2010},
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.