Quote from: tholenst on May 17, 2013, 02:54:41 PM

I suggested something similar (way later) here: https://bitcointalk.org/index.php?topic=196136

In fact, I think a reasonable solution could be implemented by adding a *single* instruction to the script language: suppose you have "OP_CHECKSIG_VAL val sig pub_key" which checks if sig is a valid signature of val under pub_key. Then you can create e.g. two transactions as follows:

TX1: Take 1 BTC from TX0out, give 0.2 BTC to Addr1, 0.8 BTC to Addr2
TX2: If you find a double spend of TX0out, give 0.2 from TX3Out to Addr1 and a fee of 10BTC to the miner

The buyer gives both transactions to a vendor who owns Addr1 who additionally checks that TX3Out really has 10.2 bitcoins and is still open. If at some point the vendor gets a double spend he can plug in the values into TX2 so that it becomes valid. Miners will be happy to mine a transaction with a 10BTC fee.

The suggestion in https://bitcointalk.org/index.php?topic=196136 is somewhat nicer because it increases the chance the vendor gets his money, but more complicated.

Explain your idea of this 10 BTC fee to the miner. Because Bitcoin is decentralized, you can't forceably withdraw Bitcoin from anybody. If you are suggesting a blacklist propagated by the miners themselves that would force withdraw Bitcoin from every transaction they would send then maybe that would prevent fraud.