@misc{cryptoeprint:2014:765,
author = {Juan Garay and Aggelos Kiayias and Nikos Leonardos},
title = {The Bitcoin Backbone Protocol: Analysis and Applications},
howpublished = {Cryptology ePrint Archive, Report 2014/765},
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.