Thanks for your reponse Loyce!
It sounds like you're planning to create a custodial wallet. That goes against everything Bitcoin stands for, and handing over private keys to someone else is the opposite of "security".
No private keys ever touch our servers. While we do enable you to make different types of encrypted backups, such as on your keychain or using social recovery. But these are opt in.
Whatever you're sending, it's not Bitcoin. Unless you're sending funded private keys, but that would be terribly insecure.
It's Bitcoin. Though you're right: when you send to someone not on the app yet, you're sending a payment link with a pre-funded private key. It's swept immediately upon onboarding.
There are no "single-use addresses" in Bitcoin. You can choose to use each address only once though. And transactions can still be linked on-chain, even if you use each address only once.
It's an implementation of Stealth addresses. It derives a single-use private key based on the shared secret, recipient's diffie-hellman public key, and recipient's root public key. And a single-use private key based on the shared secret, recipient's diffie-hellman private key, and recipient's root private key.
"Social recovery" is terribly risky. Backup your private key or seed phrase, and be your own bank. That's how you backup Bitcoin.
You're right it's not a silver bullet, but it could be a good option for some people. We'll offer different recovery methods, both "single player" and "multiplayer" like social recovery.
Why didn't you start with this? I have a really hard time believing you can do non-custodial social recoveries, so please start by explaining the technical details.
This is not live, but our latest design is: Encrypt private key with recovery contact's public key. Store on your Keychain (using iOS in this example). To recover, you need access to your Keychain and the approval of your recovery contact in the app. We also have a version using email, where the key is split among your recovery contacts and encrypted with a code emailed to you.
Let me know if you want to give it a try!