4 ms·

While I believe the author that it's measurable over the internet.. I'd love to see an example of the code on the attacking side, so I could test it for myself.

While I believe the author that it's measurable over the internet.. I'd love to see an example of the code on the attacking side, so I could test it for myself. It just seems like it wouldn't be measurable, and I'd love to test it and prove myself wrong.

kapitalx 14y ago
I've been looking at different security issues that I should protect against, and came across this article, and I also find it hard to believe that I'll need to worry about this even though the author insists that it's doable. I wonder if this is more relavant in much higher profile attacks (cyberwar,etc) than in some webapp.
- tptacek 14y ago
  It's a crypto vulnerability. Either don't write crypto code (preferred), or know about and mitigate these kinds of flaws.
tptacek 14y ago
It's very annoying to build systems to test this vulnerability. Nate Lawson presented one such system at Black Hat a few years ago; he had to modify his ethernet drivers to take interrupt overhead out of the picture, IIRC. There are very common attack scenarios where the effect you're targeting is below the measurement threshold. For instance, "across the Internet", and "target is a compare implemented by memcmp". But there are others that aren't, and ways to pivot from one to the other (for instance, "buy account at same hosting provider"). The actual attack itself, mathematically, is very simple. It's high school statistics. (Crosby & Wallach's stuff is advanced statistical filtering, but that's to get better measurements; the core of the attack is much simpler).
biot 14y ago
While only tangentially helped by timing to reduce the amount of brute force involved, you might find "How I Hacked Hacker News" interesting: https://news.ycombinator.com/item?id=639976 https://news.ycombinator.com/item?id=639976
floody-berry 14y ago
djb's "Cache-timing attacks on AES" paper includes the code he used to carry out his attacks: http://cr.yp.to/antiforgery/cachetiming-20050414.pdf http://cr.yp.to/antiforgery/cachetiming-20050414.pdf

kapitalx 14y ago

I've been looking at different security issues that I should protect against, and came across this article, and I also find it hard to believe that I'll need to worry about this even though the author insists that it's doable. I wonder if this is more relavant in much higher profile attacks (cyberwar,etc) than in some webapp.

tptacek 14y ago
It's a crypto vulnerability. Either don't write crypto code (preferred), or know about and mitigate these kinds of flaws.

tptacek 14y ago

It's very annoying to build systems to test this vulnerability. Nate Lawson presented one such system at Black Hat a few years ago; he had to modify his ethernet drivers to take interrupt overhead out of the picture, IIRC. There are very common attack scenarios where the effect you're targeting is below the measurement threshold. For instance, "across the Internet", and "target is a compare implemented by memcmp". But there are others that aren't, and ways to pivot from one to the other (for instance, "buy account at same hosting provider"). The actual attack itself, mathematically, is very simple. It's high school statistics. (Crosby & Wallach's stuff is advanced statistical filtering, but that's to get better measurements; the core of the attack is much simpler).

biot 14y ago

While only tangentially helped by timing to reduce the amount of brute force involved, you might find "How I Hacked Hacker News" interesting: https://news.ycombinator.com/item?id=639976 https://news.ycombinator.com/item?id=639976

floody-berry 14y ago

djb's "Cache-timing attacks on AES" paper includes the code he used to carry out his attacks: http://cr.yp.to/antiforgery/cachetiming-20050414.pdf http://cr.yp.to/antiforgery/cachetiming-20050414.pdf