Collaboration document for PSK Identity 02

Here we will share and organize our findings and data from #483

Findings

firmware OS SDK version did not change, but the hash and build time did
- OS SDK ver: 2.0.0(e8c5810) compiled @ Jan 25 2019 14:26:04
- OS SDK ver: 2.0.0(29f7e05) compiled @ Sep 30 2019 11:19:12
  - interesting that this build date corresponds with the release of tuya-convert 2.0, coincidence?
psk begins with 02 rather than 01
- guessing this will tell us the psk algorithm version
disabled most of the serial debugging output
- unfortunate as this was a useful reverse engineering resource
did not respond to our smartconfig procedure
- it may use a new mechanism or additional restrictions have been imposed
MAC address in flash appears to be compared with actual device MAC
- likely to foil reverse engineering attempts by running firmware on a dev board
new factory written key found in flash, "pskKey"
- this may mean the encryption key will no longer be derived deterministically, big bummer
- only found in @rsbob's backup, looks like @Farfar's was updated to this firmware and thus lacks this factory written key
  - this may mean there is still hope for devices that came with a lower firmware, since updating to this firmware would require fetching the key
  - this is a very interesting new endpoint: tuya.device.uuid.pskkey.get