@misc{cryptoeprint:2005:144,
author = {Dieter Schmidt},
title = {Kaweichel, an Extension of Blowfish for 64-Bit Architectures},
howpublished = {Cryptology ePrint Archive, Report 2005/144},
year = {2005},
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.