@misc{cryptoeprint:2012:584,
author = {Dorit Ron and Adi Shamir},
title = {Quantitative Analysis of the Full Bitcoin Transaction Graph},
howpublished = {Cryptology ePrint Archive, Report 2012/584},
year = {2012},
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.