Your edit is still a bit confused. Any halfway decent encryption algorithm and mode can encrypt terabytes of data and still be resistant to known plaintext atta

Your edit is still a bit confused. Any halfway decent encryption algorithm and mode can encrypt terabytes of data and still be resistant to known plaintext attacks. You can pretty safely use a single key to encrypt an entire hard-drive after all - that's how Bitlocker and LUKS, etc work. You don't need per file keys for encryption security or defense against known plaintext - it gives more flexibility in selectively decrypting though -- ie pay me a little money and I can prove I can return some of your shit, pay more if you want the rest.