Encrypting your backup with a passphrase and making it public is a bad idea. It is not forward secure. Anyone can try to bruteforce it offline. You better use a keyfile and backup it somewhere else, such as your other computers, external drives etc. And even then, publishing your backup is a bad idea due to possible breakthroughs in cryptography. No crypto is secure forever, you better assume that it will be broken in the next 5-10 years.