Is there a way to take key material (for example 256 random bits for an AES key) and "expand" it over to a larger amount of data? Or can I go the opposite way and take a large amount of random data and
Xor it down to 256 bits and use that (this looks like secret-sharing, but I do not know if anything changes because the "participants" would all be in the same place)?
I want to store a key, but I don't want it to be just 256 bits since it makes it hard to destroy it on certain types of media. The "key" should be a very large file such that if any portion of it on the media is damaged, the entire key is unable to be retrieved.
Just to be clear, I do not want to have "extra bits" of security. I just want to be able to have 256 bits (or whatever the algorithm is using) of security over a larger amount of storage to make key recovery on the physical storage media harder.