@misc{cryptoeprint:2010:073,
author = {Bonwook Koo, Yongjin Yeom, and Junghwan Song},
title = {Related-Key Boomerang Attack on Block Cipher SQUARE},
howpublished = {Cryptology ePrint Archive, Report 2010/073},
year = {2010},
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.