@misc{cryptoeprint:2014:837,
author = {Maciej Skorski},
title = {True Random Number Generators Secure in a Changing Environment: Improved Security Bounds},
howpublished = {Cryptology ePrint Archive, Report 2014/837},
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.