@misc{cryptoeprint:2011:084,
author = {Xingwen Zhao and Fangguo Zhang},
title = {Traitor Tracing against Public Collaboration (Full Version)},
howpublished = {Cryptology ePrint Archive, Report 2011/084},
year = {2011},
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.