Yes, this is one of the things that limits a client.
The client needs 5-of-7 mint signatures to be able to send a dbc.
The client sends 7 requests, one to each mint node (7x more work for the client than any mint node)
Each mint node signs the request (this signing operation takes about 1.347 milliseconds on my laptop, but each node needs to do it so it’s 9.429 milliseconds total network time spent generating the signatures).
The client receives 7 responses, one from each mint node (7x more work for the client than any mint node)
The client combines 5 of the 7 signatures (on my laptop takes an average of 2.233 milliseconds)
Overall the network does 9.5 ms of work for each tx, with each node individually doing 1.3 ms of work. The client has to do 2.2 ms of work, almost double the work of any individual mint node. This seems pretty reasonable to me. Clients will have much more work to do than any individual mint node.
I missed out some verifications etc but this is the broad picture; the client always does more work than any mint node.
The network only stores the spentbook, ie the identifier of each spent dbc, not the whole dbc itself.
The client is the one that writes to the spentbook, not the mint nodes. The client can never make the mint nodes do a lot of work before having done work itself.
I’m not trying to say the amplification isn’t there, I think free payments does come with risks, but it’s maybe not as big as first thought.
The main thing will be to ensure the client always does more work than the network, which will limit the effects of spam greatly.
This may mean clients might need to add some proof of work to their dbcs to act as a spam prevention (like hashcash was originally designed for), or maybe the 7-to-1 difference of mint nodes as outlined above will create enough work for clients. We’ll have to see how it goes in testnets.
Yeah this may be, but the exact transaction mechanism is still being fleshed out so going into details now is probably a recipe for future confusion. It’s tempting to write a whole lot about the cool tech (there’s some very cool stuff both in use and thrown away) but I feel just now it’s probably counterproductive.