a seller is opening a paying channel, which technically amounts to the market maker opening a payment channel to the seller (that is, the payment channel is payable to the seller)
the market maker will open the payment channel with an amount N XBR token, where the deposited amount is deducted from the sellers initial deposit/security in the respective market
consider the seller now sells data worth M XBR (where M<N)
Above is the standard process.
Now, when the payment channel is closed (say upon manual trigger from the seller side), the earned amount M (minus transaction fees) is transferred to the seller, and the channel is closed on-chain.
The latter (on-chain clearing) requires (in the market maker driven process) an on-chain transaction - and that consumes G gas (in ETH), which (again, in the regular process) is paid by the market maker.
What if G > M_ETH?
Here, the notation of M_ETH is the value of M XBR as converted to ETH.
sidenote: 2 things come into play here: the on-chain "current gas rate" (in ETH) / the actual gas paid by the market maker, and the conversion rate of XBR=>ETH. both of which are not globally unique rates, but the effective actual rates depend on the actual exchange rates (eg XBR<=>ETH), on the exchange. This is a non-trivial side aspect to follow up ..
So the "attack" here is about the seller tricking the market maker into accepting and processing paying channels and payments in a way that is net negative financially for the market maker.
Obviously, something the market maker would not want to do;)
We do already have a general safeguard in this, simply because there can be a hard minimum amount (in XBR) for payment channels (via the market definition).
That is, if PC_min (in XBR) > M (in XBR) > G (in XBR converted from ETH), everything is fine.
oberstet
commented
5 years ago
Analyze scenarios such as:
Above is the standard process.
Now, when the payment channel is closed (say upon manual trigger from the seller side), the earned amount M (minus transaction fees) is transferred to the seller, and the channel is closed on-chain.
The latter (on-chain clearing) requires (in the market maker driven process) an on-chain transaction - and that consumes G gas (in ETH), which (again, in the regular process) is paid by the market maker.
What if G > M_ETH?
Here, the notation of M_ETH is the value of M XBR as converted to ETH.
So the "attack" here is about the seller tricking the market maker into accepting and processing paying channels and payments in a way that is net negative financially for the market maker.
Obviously, something the market maker would not want to do;)
We do already have a general safeguard in this, simply because there can be a hard minimum amount (in XBR) for payment channels (via the market definition).
That is, if PC_min (in XBR) > M (in XBR) > G (in XBR converted from ETH), everything is fine.