[makomk]

Only Intel engineers know exactly how to do this and I doubt they're allowed to reveal hardware internals, but at the point RDRAND actually executes the next fewt instructions should have already been decoded and the data flow between them analyzed. In theory it's not terribly hard to use that information to change the behaviour of RDRAND.

[simias]

Honestly, and for lack of a more suitable expression, put up or shut up. If you think rdrand actually reads back the output of the RNG from RAM in order to nullify it, then show it.

It's actually possible, you can verify that the timing of the instruction conforms to what it's supposed to be doing, you can check for RAM access. RAM accesses are slow and easy to detect (I'm sure there even are hardware counters for that kind of thing on modern CPUs).

So unless you can get any kind of hard evidence that would even shed the base of the idea of a doubt about what rdrand is doing: this is pure FUD.

Finding out how rdrand is truly implemented is hard, but if it's truly the evil instruction of doom that sends images from your webcam to the NSA then it should be trivial to prove it's not behaving as it should.

[alfiejohn_]

Instead of saying put up or shut up, let's think if this is within the capabilities of Intel or an impossible feat.

First off, the RNG doesn't have to reside in RAM as it could already be in cache. So you're already not going to be detected by looking at RAM access. Also, it's not 1992. Modern architectures and modern operating systems are going to throw out instruction timings from Intel manuals. A cache miss and you're toast.

Now if you have a dedicated pipeline to executing a RNG within a code cache, all you would have to do is work out it's inverse. Very plausible.

Unless the above sounds magical, it does seem like this is a possibility. And as it's been shown that the NSA is using it's enormous budget to pay US companies to help do it's bidding, this does seem like it's within reach.