@misc{cryptoeprint:2007:203,
author = {Xin Jiang and Jintai Ding and Lei Hu},
title = {Kipnis-Shamir's Attack on HFE Revisited},
howpublished = {Cryptology ePrint Archive, Report 2007/203},
year = {2007},
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.