@misc{cryptoeprint:2011:047,
author = {Yuyin Yu and Mingsheng Wang and Yongqiang Li},
title = {Constructing differential 4-uniform permutations from know ones},
howpublished = {Cryptology ePrint Archive, Report 2011/047},
year = {2011},
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.