The firmware image is present on the computer requesting authentication. So the seed is sent to gaming machine to calculate digest at the same time the server r

The firmware image is present on the computer requesting authentication. So the seed is sent to gaming machine to calculate digest at the same time the server requesting authentication runs the same algo on stored firmware image. Provided the initial seed is random, barring weakness in the hashing algo, there is no way to beat this check. This is same process as you computing SHA1 of a file you downloaded and comparing it with the SHA1 provided on the website, if you could also provide a 128 bit number as seed of the SAH1 to the website.