@misc{cryptoeprint:2005:161,
author = {David A. McGrew and Scott R. Fluhrer},
title = {Multiple forgery attacks against Message Authentication Codes },
howpublished = {Cryptology ePrint Archive, Report 2005/161},
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.