@misc{cryptoeprint:2007:189,
author = {Meng-Hui Lim and Sanggon Lee},
title = {An Improved One-Round ID-Based Tripartite Authenticated Key Agreement Protocol},
howpublished = {Cryptology ePrint Archive, Report 2007/189},
year = {2007},
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.