@misc{cryptoeprint:2013:139,
author = {Wesley George and Charles Rackoff},
title = {Rethinking Definitions of Security for Session Key Agreement},
howpublished = {Cryptology ePrint Archive, Report 2013/139},
year = {2013},
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.