[seph-reed]

I'm piecing it together too. This is my understanding: the "model" has a set of rules (add, divide, bit shift) and that they do funky encrypted actions (add by making every third bit flip or something). If you run all of these actions in place of what you'd normally do (ie, just add like normal), then return the product, it can be decrypted as a result of the functions ran on it.

I might be wrong though.