@misc{cryptoeprint:2002:058,
author = {Palash Sarkar},
title = {Construction of UOWHF: Tree Hashing Revisited},
howpublished = {Cryptology ePrint Archive, Report 2002/058},
year = {2002},
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.