@misc{cryptoeprint:1998:001,
author = {Gerrit Bleumer},
title = {On Protocol Divertibility},
howpublished = {Cryptology ePrint Archive, Report 1998/001},
year = {1998},
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.