@misc{cryptoeprint:2008:438,
author = {Michael Gorski and Stefan Lucks},
title = {New Related-Key Boomerang Attacks on AES},
howpublished = {Cryptology ePrint Archive, Report 2008/438},
year = {2008},
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.