@misc{cryptoeprint:2004:350,
author = {Jintai Ding and Dieter Schmidt},
title = {Multivariable public--key cryptosystems},
howpublished = {Cryptology ePrint Archive, Report 2004/350},
year = {2004},
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.