@misc{cryptoeprint:2014:076,
author = {Giuseppe Ateniese and Antonio Faonio and Bernardo Magri and Breno de Medeiros},
title = {Certified Bitcoins},
howpublished = {Cryptology ePrint Archive, Report 2014/076},
year = {2014},
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.