@misc{cryptoeprint:2004:197,
author = {Helmut Kahl},
title = {SPA-based attack against the modular reduction within a partially secured RSA-CRT implementation},
howpublished = {Cryptology ePrint Archive, Report 2004/197},
year = {2004},
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.