@misc{cryptoeprint:2009:317,
author = {Alex Biryukov and Dmitry Khovratovich},
title = {Related-key Cryptanalysis of the Full AES-192 and AES-256},
howpublished = {Cryptology ePrint Archive, Report 2009/317},
year = {2009},
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.