How I Cracked the Flume Water Monitor Encryption in a Few Weeks
Flume Water Monitor 915 MHz Security Is Pretty Good
I successfully broke the encryption on the Flume Water Monitor's 915 MHz RF signal after weeks of part-time work. By combining reverse-engineering insights with a brute-force attack on a reduced 44-bit key space, I decrypted the AES-128 payload. While the security is reasonable for a consumer device, the vulnerability allows for message spoofing. Flume responded positively and shared their plans to enhance future privacy and security measures.
For a consumer water sensor, a frequency-hopping waveform combined with 44-bit effective encryption on the payload is not an unreasonable level of security.
- nabilt
So if I understand correctly, they used hard coded constants to generate keys that only have 44 bits of entropy, which is brute forcible for $10, but you have to do it per device. They presumably did this to make pairing the bridge and sensor easier while not using a static key for all devices. Not the worst compromise I guess.
I've been working on an open source solution on and off for a number of years called http://y-drip.com. It uses Wi-Fi so battery life is only a few months and range is limited. My next design is probably going to use LoRa, but this complicates things a lot because now I have two devices (bridge and sensor) that need to be paired, support over-the-air updates, etc.
What's the best way to have them share keys without adding expensive hardware like Bluetooth or NFC. The sensor also needs to be waterproof so there's no exposed ports. Increasing from 44 bits to 128 would help, but if the key generation is done over the air it can be sniffed right?
- EvanAnderson
> I reached out to Flume. They were very responsive, and their CTO shared an overview of their already-in-progress plans to further improve the product’s privacy and security.
Read: There will be a firmware update that further "secures" the device from owners who would like to use it without the "cloud" and the "app".
- ashleyn
It didn't really factor into the break here but, it's amazing people still use ECB even though the famous penguin image is well over a decade old now.
- br0ceph
i feel like it doesnt matter how secure the rf transport is, if ultimately ur data gets uploaded to a corporate cloud, and the only way to access it is through some shady cloud app
its a nice experiment, but i wouldnt say the security is good...
good security would havr everything documented with sourcecode,user generated keys, and a opensource server/client, whose code can be examined fully
- Ductapemaster
Interesting timing, I have spent the last week with Claude reverse engineering the on-air protocol and I'm getting pretty close to building a secondary "listener" receiver that will collect measurements from my bridge + sensor pair locally.
To Flume's credit, it required me to dump the firmware from the bridge device's ESP8266 in order to extract my key. I didn't consider an approach like this article took, given I have direct access to the HW and there's no flash protection on the 8266.