@misc{cryptoeprint:2005:170,
author = {Ivan Damg{\aa}rd and Kasper Dupont and Michael {\O}stergaard Pedersen},
title = {Unclonable Group Identification},
howpublished = {Cryptology ePrint Archive, Report 2005/170},
year = {2005},
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.