@misc{cryptoeprint:2006:095,
author = {John Black and Martin Cochran},
title = {MAC Reforgeability},
howpublished = {Cryptology ePrint Archive, Report 2006/095},
year = {2006},
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.