@misc{cryptoeprint:2003:038,
author = {Kazukuni Kobara and Hideki Imai},
title = {Pretty-Simple Password-Authenticated Key-Exchange Under Standard Assumptions},
howpublished = {Cryptology ePrint Archive, Report 2003/038},
year = {2003},
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.