feature: firmware with dynamic key rotation

[xudongzheng]

This has been tested with nRF52840 and S140v6. I don't have anything else available at the moment.

This is currently a draft since some refactoring is needed. I'm proposing the following

• Move common advertising-related code to lib/findmy
  • Does firmware need its own go.mod file? With it being a separate module, it seems a bit more difficult to use lib/findmy.
• Split firmware into firmware/static and firmware/rotation

There is an accompanying Python lookup script based on FindMy.py for this key rotation algorithm. However that needs to be cleaned up a bit first.

[deadprogram]

it seems a bit more difficult to use lib/findmy

Yes, I have corrected that in the most recent commits. Sorry about having to reorganize things a bit.

[deadprogram]

Interesting that you chose to use the Flash+littleFS option vs. using go:embed.

That certainly makes it easier to update the device keys remotely.

I was originally thinking to copy the adv keys to separate files in a directory, that would then be embedded into the executable at compile time.

[xudongzheng]

Thanks for the refactoring work.

Are you suggesting using go:embed to embed multiple static keys rather than 1 static key? That could be a good option for platforms with limited resources such as nRF51. I don't currently have the hardware though I do have a nRF51822 beacon on the way. It wouldn't surprise me if the key derivation fails there due to limited flash/RAM.

I've seen several firmware that do multiple static keys. I haven't had a chance to try macless-haystack yet, perhaps that's a builtin feature there?

[deadprogram]

Are you suggesting using go:embed to embed multiple static keys rather than 1 static key?

Exactly.

I haven't had a chance to try macless-haystack yet, perhaps that's a builtin feature there?

Yes, that is is correct. By populating this field in the JSON https://github.com/hybridgroup/go-haystack/blob/main/cmd/haystack/save.go#L42 apparently any of those keys will be associated with that device by macless-haystack.