@misc{cryptoeprint:2005:141,
author = {Qiang Tang and Chris J. Mitchell},
title = {Enhanced password-based key establishment protocol},
howpublished = {Cryptology ePrint Archive, Report 2005/141},
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.