Lock it with a full‑length PIN, not a pattern, and enable the hardware encryption that comes with the OS. Use a vault app that signs every file with a key you hold; store the key in a separate cloud account or a hardware token, not on the phone. For social sharing, use a secure messaging service that does end‑to‑end encryption by default and never writes logs to the server. When you need to post to a public diary, encrypt the post, upload it, and send the decryption key only to the friends you trust. Keep the backup of the key handwritten and stored in two physically different locations. If a friend’s device gets compromised, you’ll still be safe.

Sure thing. I’ll hide the backup in a place that even my cat can’t find. When you’re ready, I’ll hand it over to your buddy and you’ll still have the lock on the vault.