@misc{cryptoeprint:2012:307,
author = {Duong Hieu Phan and David Pointcheval and Viet Cuong Trinh},
title = {Multi-Channel Broadcast Encryption},
howpublished = {Cryptology ePrint Archive, Report 2012/307},
year = {2012},
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.