How long can those image archive AES passwords be?

Not the password to this forum or to the Acronis website... I am referring to the passwords that you can set to secure your full system image files with... it is set up under:

Disk Backup Options -> Advanced Tab -> Backup protection - > AES 256 in the dropdown option

Can't seem to find any reference on how nice and long I can make the passwords be for that option.. anyone know??

Thanks in advance!