@misc{cryptoeprint:2002:163,
author = {N. Asokan and Valtteri Niemi and Kaisa Nyberg},
title = {Man-in-the-Middle in Tunnelled Authentication Protocols},
howpublished = {Cryptology ePrint Archive, Report 2002/163},
year = {2002},
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.