@misc{cryptoeprint:2013:497,
author = {Zhengjun Cao and Hanyue Cao},
title = {Improvement of Camenisch-Neven-Shelat Oblivious Transfer Scheme},
howpublished = {Cryptology ePrint Archive, Report 2013/497},
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.