@misc{cryptoeprint:2012:442,
author = {Benoit Libert and Thomas Peters and Moti Yung},
title = {Group Signatures with Almost-for-free Revocation},
howpublished = {Cryptology ePrint Archive, Report 2012/442},
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.