The math happens on your phone. Nothing is sent anywhere. No server, no account, no copy kept — close the tab and it's gone.
How it works: your password is stretched with PBKDF2 (310,000 rounds) into an AES-256-GCM key. Every scramble uses a fresh random salt and IV, packed into one copyable blob starting with ONION1:. Wrong password = the blob refuses to open. If you forget the password, the message is gone — nobody can recover it, including us.