As stated in my bio, besides computer security I also love fligh simulators and mountain biking. Last year I gave a talk about hacking a flight simulator (among other games), it was only fitting to research something related to my other hobby too. Old day's bike speedometers have evolved quite a bit, and nowadays a lot of bikers (swimmers, runners, ers) do their sport with tiny computers attached to them. These computers do much more than measuring speed: they have GPS, they can store your activities, can be your training buddy, and they can communicate with various sensors (cadence, power meter, heart rate monitors, you name it), mobile phones, each other, and with PCs. One of the communication protocols used by these devices is ANT. Never heard of it? Not surprising, it is not very well known despite being utilized by a lot of gadgets including, but not limited to sport watches, mobile phones, weight scales, some medical devices, and even bicycle lights and radars. When I bought my first bike computer I rationalized it with thoughts like ‘this will help me navigate on the mountain’, or ‘I can track how much I've developed’, but deep down I knew the real reason was my curiosity about this lesser known, lesser researched protocol.
One of my favorite kind of weaknesses are the ones caused by questionable design decisions, and can be spotted without actual hands-on experience with the product itself, just by reading the documentation. Well this is exactly what happened here, I had some attack vectors ready and waiting well before I received the actual device. To top it all, I've also found some implementation bugs after getting my hands on various Garmin devices.
After a brief introduction to the ANT, ANT+ and ANT-FS protocols, I'll explain and demo both the implementation and the protocol weaknesses and reach the already suspected conclusion that ANT and the devices that use it are absolutely insecure: anybody can access your information, turn off your bike light, or even replace the firmware on your sport watch over the air.