Flume Water Monitor 915 MHz Security Is Pretty Good

Post by ivlad » Thu, Jul 30, 2026, 5:54 AM UTC

nvme0n1p1 wrote: post #8

ivlad wrote: post #4

Earlier quoted context omitted.

44 bits of security is not “pretty good”. The post author used Python, but anything more performant would result almost real-time decryption. There are no performance implications of using a proper 128 key because they are doing AES anyway. If they were resource constrained and choose a variant of TEA encryption due to constraints, it would be understandable, but no, the encryption is implemented in hardware. There a…

44 bits is horrible obviously, but maybe it's fine for this use case? The attack vector is: an adversary can get close to your water meter and after brute forcing the key, wirelessly read the numbers they could have just physically looked at the water meter to read anyway. Meanwhile the device owner can decrypt the signal and locally get access to their own data without being tied to the cloud or a proprietary vendor…

Post by ssl-3 » Thu, Jul 30, 2026, 12:10 PM UTC

ivlad wrote: post #4

Oliveaniss wrote: post #2

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 t…

44 bits of security is not “pretty good”. The post author used Python, but anything more performant would result almost real-time decryption. There are no performance implications of using a proper 128 key because they are doing AES anyway. If they were resource constrained and choose a variant of TEA encryption due to constraints, it would be understandable, but no, the encryption is implemented in hardware. There a…

Post by mrloopex » Thu, Jul 30, 2026, 12:59 PM UTC

sedatk wrote: post #12

nabilt wrote: post #7

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:…

> is probably going to use LoRa why not Zigbee or Thread?

Post by mrloopex » Thu, Jul 30, 2026, 1:02 PM UTC

Ductapemaster wrote: post #3

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 h…

Post by Ductapemaster » Thu, Jul 30, 2026, 3:48 PM UTC

elmoret wrote: post #11

Ductapemaster wrote: post #3

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 h…

If you document this somewhere I'd love to read about it! I took the approach of sniffing the packets between the radio and mcu on the bridge board, got most of the way into reverse engineering that, then helped build this instead: https://github.com/tronikos/esphome-magnetometer-water-gas-m... But I always wanted to finish pulling flume data to home assistant, without the cloud.