@misc{cryptoeprint:2012:639,
author = {Daniel Loebenberger and Michael Nüsken},
title = {Coarse-grained integer - Smooth? Rough? Both!},
howpublished = {Cryptology ePrint Archive, Report 2012/639},
year = {2012},
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.