@misc{cryptoeprint:2008:414,
author = {Matthias Fitzi and Jesper Buus Nielsen},
title = {On the Number of Synchronous Rounds Required for Byzantine Agreement},
howpublished = {Cryptology ePrint Archive, Report 2008/414},
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.