@misc{cryptoeprint:2012:438,
author = {Tetsu Iwata and Keisuke Ohashi and Kazuhiko Minematsu},
title = {Breaking and Repairing GCM Security Proofs},
howpublished = {Cryptology ePrint Archive, Report 2012/438},
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.