As was already pointed out, any protection scheme would most likely use asymetric crypto, so you can only dump the public key anyway. However there is a more pr

As was already pointed out, any protection scheme would most likely use asymetric crypto, so you can only dump the public key anyway. However there is a more pressing problem, that you would even have if symetric crypto was used: In order to extract the key you would need to know how it is encoded, which you only know once you know the plaintext of the microcode (which requires the encryption key to read the microcode updates). You run into a chicken-egg problem. Without the processor oracle, it would have been hard to impossible to start guessing the semantics of bitstrings. Also the physical ROM bits are not in the same order as the bits the CPU actually excutes during runtime. The mapping function is non trivial and we do not fully understand it yet. Finding this function required knowing what valid, plaintext microcode looks like so we could match the bitstrings from the ROM to it.