@misc{cryptoeprint:2003:173,
author = {Palash Sarkar},
title = {Domain Extender for Collision Resistant Hash Functions: Improving Upon Merkle-Damgaard Iteration},
howpublished = {Cryptology ePrint Archive, Report 2003/173},
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.