Schneier on Security

Clive Robinson • May 12, 2020 9:37 AM

@ All,

DMA attacks via I/O devices is not exactly a new thing…

I remember it being talked about back in the early 1980’s when designing Z80 based SBC rack mount boards (what we might call blades) that could be connected together via a DMS controller and high speed bus for graphics systems…

So it’s a well known problem for which Intel has no excuse what so ever. But it gets worse, from the Wired article,

Karsten Nohl, a well-known hardware security researcher and founder of SR Labs … was surprised to see how easily Intel’s “security levels” can be bypassed. “If you’re adding an authentication scheme against hardware attacks and then you implement it in unsecured hardware … that’s the wrong way to tackle a hardware security problem,” says Nohl. “It’s a false sense of protection.”

It’s a hard point to argue against. But as others might have noted Intel’s more recent history on hardware security has been quite lamentable… This suggests that maybe people should think about buying elsewhere if they can.

@ Jason Sullivan,

Idly wondering how many folks are going to be combating this particular avenue of attack with a few pennies worth of epoxy covering the flash chip.

In principle/theory it’s a good idea, in practice though it depends on “PCB Track out”. The motherboard designer may well have put a programing port or test port that is connected to those pins elsewhere on the PCB.

Clive Robinson • May 12, 2020 12:46 PM

@ Jake,

Can someone explain how this attack can bypass the encryption on a hard disk?

Technically it’s no more bypassing the encrypted hard disk than the computer is.

It’s just that with access to Kernel Space Memory it has access to all the computer it’s self can see. Thus if the computer has the Encryption keys in memory for either FDE or User/File Based Encryption then an attacker gets access to the keys or to the plaintext of any file in computer memory.

What this attack alowes an attacker to do is gain access to the plaintext beyond the security end point. So in effect it’s a form of “end run attack”.

Clive Robinson • May 12, 2020 11:43 PM

@ K. M. Peterson,

wouldn’t the workaround for this issue be to ensure it is powered down if not in your possession?

Yes and no…

If powered down you would not have encryption keys or sensitive files in memory. But that would not stop an evil made over writing the flash ROM to insecure, so that an easier faster attack can be carried out later.

It would after all then only take a few seconds to attach a quite small RF device whilst you were distracted in a coffee shop or café etc…

You’ve probably seen some very small “USB WiFi dongles” if I pushed something the same size as one in the back of your laptop whilst you were destracted you probably would not notice it as you carried on working. At the very least it could then add other malware, but also provide a high bandwidth connection for a “RAT on steroids”.

This sort of thing is why you need to do both FDE and File level encryption as a minimum to minimize losses. Plus also running software that logs all file creation, reading, updating and deleating (CRUD) etc would help identify anomalous behaviour.

The simple fact is at the end of the day as an individual you can not stop a determined attacker especially if they are at government guard level or above or equivalent corporate level (think of what Kroll and Blackwater / Academi are alledged to do).

All you can do is mitigate against less sophisticated attackers, hence the advice about not taking consumer level equipment with you when traveling across borders etc.