This is just a quick blog post to update you on some rather interesting research that will be coming out led by Eyal Ronen. At Black Hat USA 2016 I did some teardown of the Philips Hue system, and described the possibility of a lightbulb worm.
Check this landing page which now has a draft PDF of what that became. This draft paper details how you can (1) recover the encryption keys used to encrypt the firmware updates, and thus encrypt/sign your own images, and (2) details a bug specific to a version of a range-checking protocol which allows reflashing of bulbs over longer distances. The end result is this basically solves all the roadblocks I had identified as stopping the lighbulb worm from actually happening [NB: the distance-check bug has been FIXED already in firmware updates which solves this specific spreading vector].
To me the most interesting part is a demonstration of side-channel power analysis being useful for breaking a rather good encrypted bootloader. To be clear the Philips Hue does a great job of implementing a bootloader on an IoT device… it’s one of the better I’ve seen, especially considering we are talking about a lightbulb. But it’s very very difficult to hide from side-channel power analysis and other “hands on” embedded hardware attacks, instead it’s better (but more expensive logistically) to push the solutions to the higher-level architecture. If each bulb had a unique encryption key (maybe derived from the MAC address using an algorithm on a secure server if you don’t want to store all those keys) it would provide an excellent layer of defense.
I’m working on making a description of the AES-CCM attack, which will be posted to the wiki page.
Q: What does that mean to someone using Hue, is it safe?
A: Philips released a OTA update to fix the bug that allows spreading over longer distances (October 3rd update). This is a great example of a fast response by a company who takes this stuff seriously. Basically – if I was choosing a smart light platform, I’d probably use Hue (I have a few of them in my house too).
Q: What’s power analysis?
A: This isn’t a FAQ type answer – but you can see an intro video I made. Basically we use tiny variations in power consumption of a device as it’s running to determine information about secrets held within the device.
Q: What if I want more information?
A: Please contact Eyal for more details, if you want to discuss specific questions, etc. Note the Philips-specific details (such as scripts, keys, etc) will never be released, please don’t ask for them.
Q: Does a worm exist?
A: NO. It would be extremely reckless to make such a worm, as it would be VERY hard to contain the spread should you have a bunch of Hue devices around you. Instead that research paper demo’d all the pieces, but stopped short of putting them together (we wouldn’t want a criticality accident).