@misc{cryptoeprint:2007:062,
author = {Nicolas T. Courtois and Gregory V. Bard and David Wagner},
title = {Algebraic and Slide Attacks on KeeLoq},
howpublished = {Cryptology ePrint Archive, Report 2007/062},
year = {2007},
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.