@misc{cryptoeprint:2011:227,
author = {Alexander Barg and Grigory Kabatiansky},
title = {Robust parent-identifying codes and combinatorial arrays},
howpublished = {Cryptology ePrint Archive, Report 2011/227},
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.