I believe I see the place the confusion is, however please appropriate me if I am not fairly understanding your query.

It is attainable to misread that part in Mastering Bitcoin as saying that there’s one shared revocation public key between A and B, and A has one half of the key and B has the opposite half. That is how I first understood it. It finally ends up not making sense, nevertheless, as a result of once they change secret halves, each A and B now have all the data wanted to publish their very own earlier dedication transaction and easily use the entire secret to get all the funds.

As an alternative, there are literally two completely different revocation public keys, generated individually by each events. Let’s name them revpub1 and revpub2. A has revpub1 within the output of their dedication transaction and B has revpub2 in their very own transaction. The way in which that these public keys are generated ensures that every celebration initially has solely half of the data wanted to unlock every key.

When B revokes their dedication transaction, it signifies that B is giving A the opposite secret half wanted to unlock revpub2, however B would not have the primary half of the revpub2 secret that A already has. B solely obtained the opposite secret half to revpub1.

Now, if B decides to attempt to cheat and publish their prior dedication state, solely A has all the info essential to unlock revpub2 and take all the funds. On this case, it is unattainable for B to unlock revpub2. The one factor B can do is wait to spend the output after the variety of specified blocks has handed, giving A time to penalize the cheater.