Quote from: DumbFruit on July 10, 2015, 05:24:51 PM

I thought "replace by fee" could already be hardened against double spending by the merchant dumping the whole transaction into fees if a double spend is detected.

This is a stronger protection, since the merchant gets the money.

The service creates a transaction with 200 0.001BTC inputs and the fee is 0.002 BTC (1%).

One of the transactions is for 0.001 BTC. If the attacker tries to double spend, the miner has 2 choices.

Accept the double spend, but this means that the large transaction cannot be accepted, since it spends the valid transaction.

At best the double spender can offer 0.001 in fees, but the 200 transaction passthrough has a fee of 0.002. Even if the double spender gives up the benefit of double spending, he still can't pay enough to get the miner to switch.

If the miner accepts the passthrough transaction, then the double spend fails.