Actually, the workId is derived from the transaction (not the block) in which it was published so I guess yes .. your attack would work.
While not interesting for the PoW certificates (you can very well charge back using the work cancellation button)
You would't necessarily take back the whole pool...
it might become interesting when precalculating bounties, submitting them prior to the closure of a work to get most of the bounty fund payout for one-self (remember, the fund is always distributed among all bounty submissions after the work has been closed).
Well, you could "dilute" either pool, that way, with various implications for each.
On the PoW side (again as a consequence of keeping "global" PoW chain statistics, meaning a single embedded PoW chain instead of a distinct chain for each job) you could manipulate difficulty, choke out the tx limit, etc.
On the PoB side, one could do "Trapdoor Verification" as well. It seems that the publisher of work could give a verification expression which accepts either the solution that he is seeking, or any other input values that he PKI signs in a "distinguished" and otherwise-just-nonce input. This would allow him to submit, at will, his own PoB certificates which are not solutions and which no-one else can submit without his key.
This is particularly useful if your work job only seeks 1 solution - as soon as you see such a tx on the network you claim the rest of the bounties for yourself. (Or you claim "the rest + 1" bounties for yourself and try the race.)
I am starting to fix that right away!
I think an effective solution to both cases should be pretty straightforward, though the latter "trapdoor" scenario is a bit tricky, and might resurface in various forms, shortly.
Actually, I am right now filling the entire 12 integers of "possible input entropy" but not the entire memory space. If required to do so, we could go this way, even though this would increase the overhead noticably. Right now it's pretty handy to have large parts of the memory "nulled".
I am really eager to hear about this attack
As I said, I intend to go in "order of interesting-ness" and that one is awfully interesting.
I hope (and I really believe) that with your help we can get rid of most (all?) these problems
Arguably you could make my list into 3 lists. In decreasing order of size these would be: problems that I can already give solutions for, problems for which I do not have solutions for but for which I suspect practical solutions might exist, and problems that I do not think will have practical solutions in the contemporary state of the art.
Also, I am really excited to hear about your next discoveries and start brainstorming about ways to conquer them.
After all, you have my sincere appreciation for your help!!
I should be ready to throw another round of (both uninteresting and interesting) problems at you soon.
Already fixed.
