Nice post and amazing explanations!
I have a question: You told us, you don't like the architecture of Hivesigner because they store the keys on a web server
So, how do Hive Keychain and HAS handle the keys securely, because I think Hive Keychain is storing the public and consented private keys on their servers, what makes them different?
Absolutely not: Hive Keychain stores your keys encrypted in the encrypted storage of your device, they can only be unlocked with your pin and/or biometrics. @arcange's HAS system and his new Hive Authenticator app (which can be used as an alternative key store to Hive Keychain) also never takes your keys off your own device.
This is the fundamental beauty of Hive: you never have to entrust your keys to a machine outside of your direct physical control if you don't want to (and you shouldn't).
My app (and most others on Hive) pass a message to Hive Keychain, you click "sign" and then the message comes back and my app checks that the signature could only have come from someone who knows your key. I never see the key.