@misc{cryptoeprint:2014:1011,
author = {Alex Biryukov and Ivan Pustogarov},
title = {Proof-of-Work as Anonymous Micropayment: Rewarding a Tor Relay},
howpublished = {Cryptology ePrint Archive, Report 2014/1011},
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.