@misc{cryptoeprint:2015:600,
author = {John Kelsey and Kerry A. McKay and Meltem Sonmez Turan},
title = {Predictive Models for Min-Entropy Estimation},
howpublished = {Cryptology ePrint Archive, Report 2015/600},
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.