<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div id="yiv9937175344"><div id="yui_3_16_0_ym19_1_1465295946366_16278"><div id="yui_3_16_0_ym19_1_1465295946366_16277" style="color:#000;background-color:#fff;font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px;"><div id="yui_3_16_0_ym19_1_1465295946366_18256">Ah, it makes a lot more sense now. Thanks.</div><div><br></div><div>-Jonathan<br></div><div id="yui_3_16_0_ym19_1_1465295946366_18298"><br></div><div id="yui_3_16_0_ym19_1_1465295946366_18299"><br></div><div id="yiv9937175344yui_3_16_0_ym19_1_1465295946366_11245"><span></span></div> <div id="yui_3_16_0_ym19_1_1465295946366_16276" class="yiv9937175344qtdSeparateBR"><br clear="none"><br clear="none"></div><div class="yiv9937175344yqt9143989787" id="yiv9937175344yqt55448"></div></div></div></div><div class=".yiv9937175344yahoo_quoted"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px;"> <div style="font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px;"> <div dir="ltr"><font face="Arial" size="2"> On Tuesday, June 7, 2016 1:50 AM, Chris McCormick <chris@mccormick.cx> wrote:<br clear="none"></font></div> <br clear="none"><br clear="none"> <div class="yiv9937175344y_msg_container">On 07/06/16 13:40, Chris McCormick wrote:<br clear="none">> On 07/06/16 12:22, Chris McCormick wrote:<br clear="none">>> > But a public-facing server would regularly be "tweeting", no?<br clear="none">>><br clear="none">>> So you'd need physical access to a public-facing server in order to<br clear="none">>> collect the<br clear="none">>> acoustic signature.<br clear="none">><br clear="none">> <a rel="nofollow" shape="rect" target="_blank" href="https://www.tau.ac.il/~tromer/acoustic/">https://www.tau.ac.il/~tromer/acoustic/</a><br clear="none">><br clear="none">> Here the same authors mention this attack:<br clear="none">><br clear="none">> "Send your server to a colocation facility, with a good microphone<br clear="none">> inside the box, and then acoustically extract keys from all nearby<br clear="none">> servers."<br clear="none"><br clear="none">Oh and on that same page they address your question directly in a way <br clear="none">that is far better and more succinct than I did:<br clear="none"><br clear="none">Q8: How can low-frequency (kHz) acoustic leakage provide useful <br clear="none">information about a much faster (GHz)?<br clear="none"><br clear="none">Individual CPU operations are too fast for a microphone to pick up, but <br clear="none">long operations (e.g., modular exponentiation in RSA) can create a <br clear="none">characteristic (and detectable) acoustic spectral signature over many <br clear="none">milliseconds. In the chosen-ciphertext key extraction attack, we <br clear="none">carefully craft the inputs to RSA decryption in order to maximize the <br clear="none">dependence of the spectral signature on the secret key bits. See also Q18.<br clear="none"><br clear="none">For the acoustic channel, we can't just increase the measurement <br clear="none">bandwidth: the bandwidth of acoustic signals is very low: up to 20 kHz <br clear="none">for audible signals and commodity microphones, and up to a few hundred <br clear="none">kHz using ultrasound microphones. Above a few hundred kHz, sound <br clear="none">propagation in the air has a very short range: essentially, when you try <br clear="none">to vibrate air molecules so fast they just heat up, instead of moving in <br clear="none">unison as a sound wave.<div class="yiv9937175344yqt4492676644" id="yiv9937175344yqtfd12935"><br clear="none"><br clear="none">Cheers,<br clear="none"><br clear="none">Chris.<br clear="none"><br clear="none">-- <br clear="none"><a rel="nofollow" shape="rect" target="_blank" href="http://mccormick.cx/">http://mccormick.cx/</a><br clear="none"></div><br clear="none"><br clear="none"></div> </div> </div> </div></div></body></html>