@misc{cryptoeprint:2015:263,
author = {Ethan Heilman. Alison Kendler, Aviv Zohar, Sharon Goldberg},
title = {Eclipse Attacks on Bitcoin’s Peer-to-Peer Network},
howpublished = {Cryptology ePrint Archive, Report 2015/263},
year = {2015},
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.