@misc{cryptoeprint:2004:174,
author = {Dan Boneh and Xavier Boyen and Hovav Shacham},
title = {Short Group Signatures},
howpublished = {Cryptology ePrint Archive, Report 2004/174},
year = {2004},
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.