@misc{cryptoeprint:2015:049,
author = {Sonia Bogos and Florian Tramer and Serge Vaudenay},
title = {On Solving Lpn using BKW and Variants},
howpublished = {Cryptology ePrint Archive, Report 2015/049},
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.