No – iOS is signed, and changing the ID would invalidate the signature.

Taking the private key from Apple with a warrant, national security letter, subpoena, or other methods is much easier than creating a custom version of iOS.

It is foolish to assume that the FBI would stop at this special version of iOS, especially given how they have been arguing and fighting to break encryption for over two decades.

edit, on icebraining's interpretation:

That's exactly right - once the difficult part about targeting an individual phone is finished, it's easy to take the iOS signing key and target any device you want.

> Taking the private key from Apple with a warrant, national security letter, subpoena, or other methods is much easier than creating a custom version of iOS.

Clearly it is not, otherwise they would have done this. They did not.

I think it's meant taking the key used to signed that custom version of iOS. That is, if the FBI can force Apple to write the custom version, they can also coerce the key from them to sign their own copies, preventing your suggested blocking mechanism.

This is what I understood, at least, from the parent's post.

And can Apple guarantee that the ID can't be changed inside the device? If they can't it makes a lot of sense for Apple to refuse creating such a tool.

The ID can be easily changed. A quick Google search will easily confirm this.

The question is can you change one devices ID to exactly match another. This might require hacking the BPP or finding a SHA1 hash collision, both of which are absolutely possible but not necessarily trivial.

Pretty much, as far as I'm aware; the device ID cannot be changed. Bear in mind that this entire discussion is applicable only to older iPhones, in any case.

That guarantee until the latest generation was the only thing protecting the hardware. It has never been altered or hacked that I am aware of. Doing so would require modifying the physical construction of the chips on the device.

Possible? Maybe, but if it was that simple the FBI could simply change the signing key. It's not, and they can't.