Subject: Re: [bitcoin-dev] [Pre-BIP] Fee Accounts

From: Jeremy Rubin <[email-masked]>
Date: Fri, 18 Feb 2022 16:38:27 -0800

> As I said, it's a new kind of pinning attack, distinct from other types
of pinning attack.

I think pinning is "formally defined" as sequences of transactions which
prevent or make it less likely for you to make any progress (in terms of
units of computation proceeding).

Something that only increases possibility to make progress cannot be
pinning.

If you want to call it something else, with a negative connotation, maybe
call it "necromancing" (bringing back txns that would otherwise be
feerate/fee irrational).

I would posit that we should be wholly unconcerned with necromancing -- if
your protocol is particularly vulnerable to a third party necromancing then
your protocol is insecure and we shouldn't hamper Bitcoin's forward
progress on secure applications to service already insecure ones. Lightning
is particularly necromancy resistant by design, but pinning vulnerable.
This is also true with things like coinjoins which are necromancy resistant
but pinning vulnerable.

Necromancy in particular is something that isn't uniquely un-present in
Bitcoin today, and things like package relay and elimination of pinning are
inherently at odds with making necromancy either for CPFP use cases.

In particular, for the use case you mentioned "Eg a third party could mess
up OpenTimestamps calendars at relatively low cost by delaying the mining
of timestamp txs.", this is incorrect. A third party can only accelerate
the mining on the timestamp transactions, but they *can* accelerate the
mining of any such timestamp transaction. If you have a single output chain
that you're RBF'ing per block, then at most they can cause you to shift the
calendar commits forward one block. But again, they cannot pin you. If you
want to shift it back one block earlier, just offer a higher fee for the
later RBF'd calendar. Thus the interference is limited by how much you wish
to pay to guarantee your commitment is in this block as opposed to the next.

By the way, you can already do out-of-band transaction fees to a very
similar effect, google "BTC transaction accelerator". If the attack were at
all valuable to perform, it could happen today.

Lastly, if you do get "necromanced" on an earlier RBF'd transaction by a
third party for OTS, you should be relatively happy because it cost you
less fees overall, since the undoing of your later RBF surely returned some
satoshis to your wallet.

Best,

Jeremy