With public key encryption, there are actually two keys used.
But the file can have multiple of these public key encryptions in its header.
Except in this case we want the effect of public key encryption without the computational overhead.
We're able to get it to the other end, even in full view, by using public key encryption.
Suddenly now we're asking it to do public key encryption, which is very processor intensive.
And the static system doesn't require a third party, doesn't have public key encryption.
Of course that's the point behind public key encryption.
Now, we've never discussed brute-force attacks against public key encryption, which is the reason this question caught my attention.
So that's why we've never discussed brute-forcing public key encryption.
It's just nobody ever attempts to brute force public key encryption.