Maker should only send their Private Key after receiving the Private Key of incoming swap

[rishkwal]

In our current implementation the maker sends the private key for their outgoing funding transaction to the taker before getting the private key of the incoming funding transaction. This creates an attack vector where the taker would always benefit from not handing over her private key to the maker.

So, in this scenario Alice could just send the Hash Preimage to Charlie and get the private keys for the multisig of the last hop(without sending anything to Bob). If she does that she can perform a coinswap without having to pay the mining fees to the makers and all the intermediate makers would lose on mining fee. And this could be done without affecting privacy of the taker.
This can be mitigated by changing the order of which privkey goes first. here in the diagram if Charlie demands to see ResPrivkeyHandover(1) then only release RespPrivkeyHandover(2) then Alice cannot withold the key or else his incoming swap will not settle.