@misc{cryptoeprint:2000:029,
author = {Anand Desai and Sara Miner},
title = {Concrete Security Characterizations of PRFs and PRPs: Reductions and Applications},
howpublished = {Cryptology ePrint Archive, Report 2000/029},
year = {2000},
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.