Monday, 30 January 2017

Should You Worry About Your Oculus Sensor Spying on You? We Asked the Expert

Image: Oculus

On Saturday we published a story about how it's possible to pull images from the Oculus Rift's tracking "sensors," which are essentially just low quality webcams. We here at Motherboard encourage vigilance at all times, and so were understandably worried that this discovery might allow hackers to see us while we're taking a virtual walk on the wild side.

But how worried should we be? To find out, we got in touch with UC-Davis researcher Oliver Kreylos, who discovered how to pull images from Oculus Rift sensors. He got back to us with very detailed answers not just about this particular hack, but VR tracking sensors in general. We found them to be very interesting, so we're sharing the email interview below in full.

Motherboard: Compared to the Vive's Lighthouse sensors, is the Oculus' method of position tracking comparatively sloppy, or would you say it has its benefits? As in, is it even worth it for Oculus to be taking these kinds of risks in its product?
Oliver Kreylos: This is a bit of a loaded question, so I'll have to establish some context to give it a fair answer. Cameras and tracking markers (such as Oculus' LEDs) are a long-established approach to 3-DOF (position only) and 6-DOF (position and orientation) tracking. [DOF stands for Degrees of Freedom, a system that mimics the visual sensation of looking around your body.] Almost all high-end motion capture systems are based on it. It was the foundation of the Wiimote's tracking, and it's been used for PC games in the form of NaturalPoint's TrackIR head tracker for many years.

The reason this method is so popular, especially among the hobbyist crowd, is that it delivers high quality results while only requiring little custom hardware. Cameras are ubiquitous and cheap, and the only other hardware component are rigid arrangements of tracking markers, which even hobbyists can build (see this old Wiimote project of mine). Everything else is done in software.

When Oculus needed a good and cheap 6-DOF tracking system for the Rift DK2 [Development Kit 2], cameras were the obvious and most appropriate choice. But instead of delivering a standard implementation, Oculus went the extra mile and delivered an ingenious variation which significantly reduced the computational load of the standard algorithm by designing tracking LEDs that could identify themselves to the camera (see here for all the gory details). As a result, the DK2 tracking system exceeded many people's expectations, including my own.

When Oculus moved from DK2 to CV1 [Consumer Version 1, or the first version used by buyers after the official launch], keeping the existing proven tracking system, and further improving it by employing better hardware (higher-resolution camera, global instead of rolling shutter), was a sound engineering decision. From a purely technical perspective, it was the correct decision. While there are some problems, Oculus' Constellation is an excellent 6-DOF tracking system. Due to Constellation's comparative closedness, I have not analyzed it as thoroughly as Valve's Lighthouse system, but I am expecting them to be about on par quality-wise.

That said, I rate Lighthouse as the more elegant of the two systems, in the sense that it collects less raw data, and has to do less processing, to deliver the same end result. The basic input for both systems' position calculation algorithm are three-dimensional rays starting at a central point— the camera focal point or the Lighthouse base station center—and pointing towards tracking LEDs or photodiodes in space. Constellation calculates these rays by capturing high-res images, streaming them to the host PC, finding blobs of bright pixels in those images, and calculating the (x, y) positions of their centers. Lighthouse does the same by timing when a sweeping laser hits a photodiode [a device that converts light into an electric current], converting times into angles based on the lasers' known angular velocity, and sending the resulting angles to the host PC. Constellation needs to send around 60 MBs of data per camera to the host, which puts severe stress on the host's USB subsystem, whereas Lighthouse sends so little data—I estimate tens of KBs—that it can do it wirelessly without causing issues.

But that does not mean Constellation is sloppy. It was a top-notch state-of-the-art system when it was developed, but Valve unveiled an unexpected and more elegant system at a time when it was too late for Oculus to change course. It was an ingenious bit of innovation that I don't believe anybody saw coming.

The main downside of Constellation is that it causes issues for some users due to its high USB bandwidth demands. The other, non-technical, downside is that it sends high-resolution images from several cameras to the host PC, and that those cameras, by necessity, have to be placed in almost ideal surveillance positions. I personally believe that the risk of some attacker gaining access to these images is minimal, but I cannot deny that it is theoretically possible.

This is the one aspect where Oculus could have done differently to avoid this issue entirely. I mentioned the Wiimote above, and that it also uses a camera (on the Wiimote) for tracking. But unlike Constellation, the Wiimote does not send images to the console for processing. The step that converts images to (x, y) LED positions is done inside the camera chip itself, by a custom piece of silicon. If Oculus had followed this approach and integrated such ASICs [application-specific integrated circuit, or a custom-designed circuit with a specific use] into the cameras themselves, they could have avoided both of Constellation's issues. It would have reduced bandwidth from the cameras to the host by a factor of about 1000 (and fixed most users' issues), and it would have made it impossible to snoop images, because the images would never have been sent to the host PC in the first place.

I do not know whether this was "sloppy," in the sense that Oculus engineers overlooked the privacy concerns users might have, or if they weighed the risks and benefits and made an informed decision. There are benefits of sending images to the host: designing an ASIC takes time and money, software solutions are more flexible and easier to improve over time, and it is possible that Oculus are currently working on algorithms to use the camera images to track more than just LEDs, for example to bring user's hands or even full bodies into VR à la LeapMotion or Kinect.

As an aside, Oculus have consistently been referring to the CV1 cameras as "sensors" instead of cameras, and have insisted that they do not work like cameras. Initially, that made me think that they had indeed integrated image processing ASICs into the cameras, but that turned out to be false.

Do you know if it's possible to capture "images" with the Vive's sensors even without traditional cameras?
Lighthouse itself does not collect any data that would make it possible to reconstruct an image of the user's environment, or of the user itself. The only data sent from Lighthouse trackables to the host PC are timestamps at which individual photodiodes on the trackable are hit by sweeping lasers, and samples from the trackable's integrated inertial measurement unit, which together allow establishing the trackable's position and orientation in 3D space. Theoretically, by observing the position of all trackables over a long time period, one could reconstruct a rough 3D model of the user's environment (i.e., where walls or major obstacles are), but that is about it.

That said, the Vive headset does have a front-facing camera that is a standard webcam, and is advertised to the host PC's operating system as such. This camera is therefore exactly as vulnerable to exploits as any other webcam connected to a computer. Unlike Constellation's cameras, however, this one is not required for the overall VR system to function, and users concerned about privacy could disable it without negative consequences simply by covering it with a piece of tape.

Would you say the complications of the process to get a recognizable image (and the comparative limitations of the hardware's availability) is enough to dissuade the hacking of the sensors on a large scale?
I cannot make a judgment as I'm not a computer security expert. I know that there are real cases of remote attackers gaining access to webcams, but I do not know how those attacks were done, and whether those methods would work with the Constellation cameras. The approach I followed was

simple, but would probably not work for a remote attacker as it required patching the Linux kernel's webcam driver to recognize the Constellation camera.

One thing I can say is that "standard" webcam attacks that might be out in the wild and be widely deployed will not succeed with the Constellation cameras, as they do not advertise themselves to the OS as standard webcams. If a generic webcam exploit were to run on an Oculus user's computer, it would not find them. That said, due to the Constellation cameras actually being standard webcams under the hood, exploits could be modified to target them nonetheless, but I do not know whether this would require small or large modifications.

Another complication for a would-be attacker is that the Constellation cameras are used by Oculus' run-time software while the headset is active. Existing webcam exploits might not be able to take over if another process is already using the cameras, or might shut down tracking in doing so, which would alert the user to shenanigans. In addition, each Constellation camera has an activity light on it. I do not know whether those are tied into the camera sensor's operation at an electric circuit level, but I do know that my camera's light turned on when I started recording images from it with my software.

Hope this helps.

It Does. Thank you!

from Should You Worry About Your Oculus Sensor Spying on You? We Asked the Expert

No comments:

Post a Comment