On Mon, Oct 05, 2015 at 06:46:28PM +0200, Mike Hearn via bitcoin-dev wrote: > The example is this: find someone that accepts 1-block confirmed > transactions in return for something valuable. There are plenty of them out > there. Once the soft fork starts, send a P2SH transaction that defines a > new output controlled by OP_CLTV. It will be incorporated into the UTXO set > by all miners because it's opaque (p2sh). > > Now send a transaction that pays the merchant, and make it spend your > OP_CLTV output with an invalid script. New nodes will reject it as a rule > violator. Old nodes won't.
Old nodes running bitcoind will see it as OP_NOP2, and will reject it unless they've manually disabled SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS, which (aiui) has been available since bitcoin 0.10 [0], but not backported to 0.8 or 0.9. [0] https://github.com/bitcoin/bitcoin/commit/0391423 That covers about 4700/5880 nodes going by bitnodes.21.co; but I can't tell how many miners it covers. Further, AIUI, nodes running 0.8 or 0.9 will still apply IsStandard() checks to scripts attempting to spend p2sh outputs [1], so will also fail to either mine or relay your OP_NOP2 payment. [1] https://github.com/bitcoin/bitcoin/commit/6259937 > So at some point an old miner will create a > block containing your invalid transaction, the merchant will think they got > paid, they'll give you the stuff and the fraud is done. My understanding is that this isn't supposed to be a problem because you won't be able to find an old miner that will do that; released versions of bitcoin already block it by default. Sure, someone could disable those checks and not pay attention to a soft fork that will cause their blocks to be orphaned, but I'm not seeing why that's any different a threat compared to someone deliberately mining invalid blocks to do 1-confirmation doublespends against merchants not running a full node. At least, that's my understanding, and I'm not an expert, so corrections appreciated. Cheers, aj _______________________________________________ bitcoin-dev mailing list bitcoin-dev@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
