@misc{cryptoeprint:2012:400,
author = {Philipp Jovanovic and Martin Kreuzer and Ilia Polian},
title = {An Algebraic Fault Attack on the LED Block Cipher},
howpublished = {Cryptology ePrint Archive, Report 2012/400},
year = {2012},
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.