Some notes on this:

We need to use an updated and peer reviewed library to do this. @JBassett says he looked at https://github.com/terl/lazysodium-android, one option I suggested. The other option is https://github.com/joshjdevl/libsodium-jni. Sadly, both are Java. The only Kotlin option hasn't been updated in 2+ years.
Initial support has been added to HA Core to enable encryption on existing registrations (at Add new webhook action to allow enabling encryption in an existing registration core#31743). Call webhook action enable_encryption on HA Core 0.106+, receive a JSON body with secret as the response. HA version can be derived via get_config webhook action. The logic in app should look like this (psuedocode):
```
if app_has_no_encryption_key and ha_version > 0.106:
    attempt_to_enable_encryption()
```
If enabling encryption fails due to older HA version, then we should either keep doing that check every so often (whenever app starts?) or have a button in settings to allow users to manually enable encryption.

Support encrypted communication with HA #97

Description