@misc{cryptoeprint:2005:073,
author = {Nam-Su Jho, Jung Hee Cheon, Myung-Hwan Kim, and Eun Sun Yoo},
title = {BROADCAST ENCRYPTION $\pi$},
howpublished = {Cryptology ePrint Archive, Report 2005/073},
year = {2005},
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.