Thanks to VeeMiner, that pointed me to the paper:
http://people.scs.carleton.ca/~clark/biblio/bitcoin/Karame%202012.pdfI learned some interesting facts:
1) It is relatively EASY AND CHEAP to cheat a merchant with double spending if he doesn't wait more than a few seconds to validate the transaction with 0 confirmation.
Ah, this is NOT theory, the researchers MADE IT HAPPEN (to themselves) to confirm the predicted attack success probabilities. With just a handful of malicious peers, one connected to the merchant directly and a few helpers (<10 was more than enough)
2) The only really proper and reliable FIX is to add a very simple CHANGE to the protocol, that is:
When the researchers could perform their test attacks, the bitcoin network was accepting any first valid transaction that arrived to them and discarded the others that arrived later SILENTLY. ( I WONDER WHY??? it seems quite a stupid thing to do not TO REPORT this EVENT through the network)
The SOLUTION is as simple as just to REPORT back to the network of peers any detected double spending as soon as two or more transactions that are still not in a block get received for the same inputs. I would say also all those transactions should be penalized by not making it to the next confirmed block at least.
The researchers say that the protocol already contains a transactions alert message that was unused at the moment and could become the double spending alert. So the change would be minor indeed.
I think this is quite IMPORTANT. Supporting such alert messages would expand bitcoin use cases to instant transactions like buying stuff at the supermarket, paying your bread, etc. The merchant could be quite confident that in 10-20s or less there is no double spending alert the probability that the transaction will get confirmed is quite sure.
So the question is...
Does current bitcoin support double-spending alerts?
If so, where can I read about it?
If NOT? why?
What is the reason? (Are you crazy? what are we waiting for?)
AND THANKS again to VeeMiner FOR POINTING me to this paper!!!