@misc{cryptoeprint:2014:398,
author = {Taylor Daniels and Daniel Smith-Tone},
title = {Differential Properties of the HFE Cryptosystem},
howpublished = {Cryptology ePrint Archive, Report 2014/398},
year = {2014},
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.