@misc{cryptoeprint:2008:090,
author = {Mridul Nandi},
title = {Improving upon HCTR and matching attacks for Hash-Counter-Hash approach},
howpublished = {Cryptology ePrint Archive, Report 2008/090},
year = {2008},
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.