Flume Water Monitor 915 MHz Security Is Pretty Good

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?

> 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".

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.

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

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.

Flume seems like a great company and product. They have always been really responsive when I contacted them. My meter gets submerged in water from time to time, so I was sure to seal it with silicon grease and tape.

As usual, the weak point is key generation and management.

is this website loads text on the fly or something?

it is full-on broke on my phone, showing only pictures and no text

One thing I appreciate about this kind of research is that it doesn't assume every wireless protocol must end with a catastrophic vulnerability.

A result of "the security is actually pretty good" is arguably just as valuable as finding a critical flaw. It helps distinguish between systems that are merely proprietary and those that were designed with a reasonable threat model in mind.

I'd be interested to know where the remaining weaknesses lie. Are they primarily in the RF protocol itself, key management, device provisioning, or the surrounding cloud infrastructure? In many IoT systems, the radio protocol ends up being the strongest component while the weakest link is somewhere else entirely.