@misc{cryptoeprint:2011:575,
author = {Jing Liu and Changji Wang},
title = {Exclusive Key Based Group Rekeying Protocols},
howpublished = {Cryptology ePrint Archive, Report 2011/575},
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.