@misc{cryptoeprint:2010:391,
author = {Daniel Z. Zanger},
title = {Exponential Bounds for Information Leakage in Unknown-Message Side-Channel Attacks},
howpublished = {Cryptology ePrint Archive, Report 2010/391},
year = {2010},
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.