@misc{cryptoeprint:2013:256,
author = {Yannick Seurin},
title = {On the Lossiness of the Rabin Trapdoor Function},
howpublished = {Cryptology ePrint Archive, Report 2013/256},
year = {2013},
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.