Quote from: iddo on June 16, 2015, 03:15:33 PM

If the merchant accepts then it's 0-conf security

He accepts a block with the transaction. It is 1 conf, but not 0-conf

Quote from: iddo on June 16, 2015, 03:15:33 PM

If all these different valid blocks don't offer any particular reward to specific addresses, then it's just DoS attack as discussed in section 5.1 of the PoA paper. If the attacker does wish to mix things up by incentivizing different participants to work on diffferent forks, then I tried to explain to you how to accomplish this attack more easily in Bitcoin.

The paper says that nodes "ban all blocks (blockheaders) with the last Nth stakeholders", but that can happen only if they will discover such headers. Imagine:
All nodes are connected as bipartite graph (every "red" node is connected to a "blue" node, but there is no "red"-"red" or "blue"-"blue" connections)
Attacker sends different blocks to all red nodes, remember, there is no connection between red-red nodes, so red nodes relay blocks only to blue nodes. Each blue node will ban this header. But how can red nodes know about it?
We will need to implement some kind of alert system to avoid new DoS attack vectors. Can you ban the node for sending 2nd, 3rd, 4th ... block with the same header?

I don`t think that system with a user, who can create unlimited number of blocks "for free" will run perfectly.
Can see a problems here and solutions can cause new problems.
I think that future DIgitalNote type of PoA implementation will have no such a treat.
Thank you for answers and your work, please, comment any possible issues with XDN PoA idea.