If you're using a truly random password of 64 characters in length that spans all 94 ascii printable characters (excluding whitespaces), then your password is much stronger than 256 bits. It's more on the order of 420 bits.
Originally Posted by GrantStoner
Password entropy can be calculated with the following formula:
Congratulations on having a phenomenal memory!
log2(n) * l
Where n = number of possible characters in password
Where l = length of password
You do it during the install. I believe the options are AES, Twofish, and Serpent. All offer 128, 192, or 256 bits, iirc.
And you said you can change the algorithm from within the menu? Is this the menu as you're installing Ubuntu? Or is there some kind of menu within Ubuntu I can use to change preferences?