I don't... you just seem really confused here :(. You are conflating the key used to sign the data on the disk with the key used to sign a software update for the system; the FBI here wants firmware for the device, signed to work on this device, that will allow them to brute force the PIN code (or password) used to generate the disk encryption key. I am saying that the actual software is something that many people in the community could build, and would require almost no effort for Apple to produce. The only reason I, in fact, can't do this, is because I don't have a key that Apple is sitting in possession of right now: the key that is used to sign these firmware updates. That one key is the backdoor, as that key is the only thing standing between someone and accomplishing what the FBI wants, and it will let you do not only this but all kinds of other evil things you want to do to anyone's phone.