@misc{cryptoeprint:2008:515,
author = {Thomas Fuhr and Thomas Peyrin},
title = {Cryptanalysis of RadioGatun},
howpublished = {Cryptology ePrint Archive, Report 2008/515},
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.