@misc{cryptoeprint:2014:636,
author = {Vikram Singh},
title = {Improved Timing Attacks on ECDSA},
howpublished = {Cryptology ePrint Archive, Report 2014/636},
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.