@misc{cryptoeprint:2013:804,
author = {Mohammad Saiful Islam Mamun and Atsuko Miyaji},
title = {Group Signature with relaxed-privacy and revocability for VANET},
howpublished = {Cryptology ePrint Archive, Report 2013/804},
year = {2013},
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.