@misc{cryptoeprint:2012:486,
author = {Michael Backes and Ankit Malik and Dominique Unruh},
title = {Computational Soundness without Protocol Restrictions},
howpublished = {Cryptology ePrint Archive, Report 2012/486},
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.