Apple is outright lying here. "the technique could be used on any number of devices" - not since the iPhone 3GS! https://www.apple.com/customer-letter/answers/ …
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@maciekish The fact is Apple is fully in control - both of the firmware signing key and the device personalization (SHSH) key, either way.
@maciekish In other words, the "master key" isn't the tool - they already own the master key and you already need to trust them.