Ninjastic
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Board Development & Technical Discussion
Re: Doubt about double spending
by
PrimeNumber7
on 30/09/2021, 05:41:28 UTC
Quote from: n0nce on September 28, 2021, 09:37:13 PM
Quote from: Csmiami on September 28, 2021, 09:29:45 PM
[...]
I know transactions with RBF can be double spent (or accelerated, call it however you like it most), but is there any other way to actually do this? CPFP is a kind of RBF, IIRC; so, if transactions that don't have RBF active can not be double spent, could hypothetically a casino run a node that is able to tell if a transaction has this activated, and in the event of it being negative, instantly credit the money with no confirmations required?
Oh no, please no Cheesy Don't confuse RBF with double-spend attacks! That's totally not the same thing.
If I am not mistaken, there is no technical reason why a RBF transaction cannot be double-spent in a way that results in entirely different outputs than the original transaction. Most wallet implementations will not allow for this, so you will have to have some technical know-how in order to create this kind of double-spend transaction. AFAIK, there are ~zero businesses that accept 0-confirmation RBF transactions, so there is really not much incentive for anyone to create these types of malicious double-spends.

Quote from: o_e_l_e_o on September 29, 2021, 12:38:16 PM
Quote from: nc50lc on September 29, 2021, 04:13:00 AM
If it has an unconfirmed parent(s), any of the parent transaction shouldn't be marked as replaceable as well.
You shouldn't really accept zero confirmations for any transaction which has any unconfirmed parents regardless of their RBF status, since transaction malleability would allow a miner to invalidate the child transaction without invalidating/double-spending the parent transaction(s) (unless all the unconfirmed parents only spend bech32 segwit inputs).
The issue of transaction malleability was solved via BIP66. Further, as you note, SW parent transactions are not maileabile.

Quote from: Csmiami on September 28, 2021, 09:29:45 PM
CPFP
CPFP is when the output of an unconfirmed transaction is spent in a transaction with a high enough fee such that the total fee in both transactions is high enough (when considering the total size) to get both transactions confirmed based on the current fee market. A casino could potentially offer to create a CPFP transaction for customer deposits as a "service" they charge for in order to get their deposit transactions confirmed more quickly.

Also, if a casino requires their customers to have accounts, they can extend "credit" to their long-standing customers who have a history of having their deposits confirm, and charge a "fee" for taking on the risk the deposit is double spent in a way that the casino does not receive the deposit.