pretty good presentation on that by djb: <a href="https:&#x2F;&#x2F;projectbullrun.org&#x2F;surveillance&#x2F;2015&#x2F;video-2015.html#bernstein" rel="nofollow">https:&#x2F;&#x2F;projectbullrun.org&#x2F;surveillance&#x2F;2015&#x2F;video-2015.html...</a>