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Within the ephemeral anchors draft BIP (additionally mentioned right here) it states that with out V3 transactions an adversary can enhance the required charges to interchange a transaction as a lot as 500 occasions. That sounds lots. What’s the precise situation the place there can be a 500 occasions enhance?
Sure it’s, that is why “economical pinning” can also be a problem. Requiring a excessive sufficient payment enhance is similar to stopping you from changing altogether. And should you really change it, this did not price them something to carry out this assault within the first place.
To offer you an instance, let’s take a
200vb transaction with a
2_000sats payment (
10sats/vb). If an attacker can change it by a
100_000vb model of this transaction that pays a
1_000_000sats payment, the most affordable manner by the present substitute guidelines to bump the feerate of this transaction is to pay
1_000_200sats for the unique
It is a
5001 issue enhance in feerate, and a
500.1 issue enhance in absolute charges to have the ability to change the transaction.
The instance given in version3_transactions.md exhibits learn how to get a payment price enhance of 100x, however should you assume transaction B is 200vB, as an alternative of 1000vB, you can even exhibit a 500x enhance with that instance (copied beneath).
“Rule 3” Pinning
RBF guidelines require the substitute transaction pay the next absolute payment than the mixture charges paid by all unique transactions. This implies Mallory might enhance the charges required to interchange B by:
- Including transaction(s) that descend from B and pay a feerate too low to fee-bump B via CPFP.
For instance, assuming the default descendant measurement restrict is 101KvB and B is 1000vB paying a feerate of 2sat/vB, including a 100KvB, 2sat/vB baby will increase the fee to interchange B by 200Ksat.
- Including a high-fee descendant of B that additionally spends from a big, low-feerate mempool transaction, C. The kid might pay a really giant payment however not really be fee-bumping B if its total ancestor feerate continues to be decrease than B’s particular person feerate.
For instance, assuming the default ancestor measurement restrict is 101KvB, B is 1000vB paying 2sat/vB, and C is 99KvB paying 1sat/vB, including a 1000vB baby of B and C will increase the fee to interchange B by 101Ksat.