Anyways: How are the keys for the files generated?
It's a random string not hash

Of which length and how generated (/dev/random, /dev/urandom, some library...)?!
How and where are these keys stored?
He said AES-256, which means the key size is always 256 bits.
Anyways: How are the keys for the files generated?
It's a random string not hash

More importantly, where are your keys stored?