@misc{cryptoeprint:2013:573,
author = {Leibo Li and Keting Jia and Xiaoyun Wang},
title = {Improved Meet-in-the-Middle Attacks on AES-192 and PRINCE},
howpublished = {Cryptology ePrint Archive, Report 2013/573},
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.