I want to use a very long (20+ char), strong password for my FileVault 2 full disk encryption (as well as encrypted Time Machine backups stored on a network drive), which should protect against brute force attacks on the disk should it fall into the wrong hands. I'm not concerned about cold boot attacks or attempts to physically freeze the ram and directly access its contents etc.
However, I don't want to have to enter the very long password every time I unlock the screen saver or
sudo in the terminal - a moderately strong (and much shorter) password will suffice.
How can I somehow configure things so that while the Mac is running I can use the short password but for unlocking it at boot time only the long password will work?