90 bits, clean source, is bare minimum. Better to push up to 128 bits. A 10-word diceware passphrase is often recommended. If you choose a password rather tha

90 bits, clean source, is bare minimum. Better to push up to 128 bits. A 10-word diceware passphrase is often recommended. If you choose a password rather than a passphrase, the bare minimum is 15 (90 bits) to 22 (128 bits) characters, upper and lower case and numbers. Either way, purely random is key here.