@misc{cryptoeprint:2003:089,
author = {Christopher Wolf},
title = {Efficient Public Key Generation for Multivariate Cryptosystems},
howpublished = {Cryptology ePrint Archive, Report 2003/089},
year = {2003},
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.