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Comment by mrb | Hacker News Reader

That's great, but using a 64-bit key in 2017 isn't "taking security seriously". Especially if you are designing meters that will have a lifespan of 10+ years, therefore must be secure until 2027 and beyond.

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Our most talkative meters are currently broadcasting 4 packets of data per hour. Water meters with autonomous power are limited to one or two (for central hot water supply) packets per day. With all the randomness added collecting data for successful key bruteforcing will take months or even years. On the other hand, using 64 bits allows us to use 16- or even 8-bit microcontrollers, which is beneficial to power consumption. Of four recources commonly metered in Russia - electricity, water, gas and heat - three should use autonomous power. We also making an autonomous plug-in modules for popular "dumb" electricity meters - to simplify installation. They broadcast once a day too so the battery could last for 6 years.

I can't speak to the specifics of your project, but 128-bit symmetric crypto on 8-bit microcontrollers is perfectly possible, at a low power budget and with relatively small code and RAM usage.

When we were looking at the task of creating autonomous battery-powered reasonably-sized device with 6 years lifespan - we took into consideration every single point where we could conserve power. Now we have what we have, not what you think we could have. Feel free to try and break our encryption with couple kilobytes of ciphertext on hands - you will have a prize of reading your neighbour's water consumption data on a daily basis)

> Of four recources commonly metered in Russia - electricity, water, gas and heat

When you say "heat" - is this steam from a combined heat & power plant? I was aware these were quite widespread in Russia but didn't know they were metered.

No, not steam, just hot water. Yes, mostly from heat & power plants, but sometimes from gas-powered local boiler plants. They are metered on per-building basis, but there's technical possibility to install individual meter and pay only for actual consumption.

It's fairly common in eastern and northern Europe too. In my building there is a single heat pipe from the city, however each unit has it's own meter for cold water, hot water (for taps) and hot water (for heating). The hot water meters are different in that the first measures the water flow, and the later measures the heat flow.

Does it recycle the cooled water back into the system?

Still, the comment above still stands. Not sure about the key bruteforcing estimates, surely a couple of days of readings would be enough.

Are the keys stored on the devices? Is it a shared key?

Every device has it's own unique keys - one for transmitting data and another for receiving commands. They are burned with firmware in production. If you are interested in bruteforcing - I can send you two weeks worth of my home water meters' data packets to play with :) See, the CRC is calculated for encrypted data, so there is no way to know if the guessed key is correct.

No MACs?

There are unique device Ids, they kinda like MACs.

Old thread, but GP probably talked about a different thing. Not MAC as in Ethernet..

https://en.m.wikipedia.org/wiki/Message_authentication_code

Oh, those MACs) No, we've spend that bandwidth for iterators to mitigate replay attack. But the idea of one-time MAC is interesting, thank you.

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