[bitcoin-dev] Revisiting BIP 125 RBF policy.

Russell O'Connor roconnor at blockstream.io
Thu Mar 8 20:07:43 UTC 2018

On Thu, Mar 8, 2018 at 1:34 PM, Peter Todd <pete at petertodd.org> wrote:

> On Thu, Mar 08, 2018 at 10:39:46AM -0500, Russell O'Connor wrote:
> > On Thu, Mar 1, 2018 at 10:11 AM, Peter Todd <pete at petertodd.org> wrote:
> > > I mean, I think in general solving this problem is probably not
> possible.
> > > Basically, the fundamental problem is someone else has consumed network
> > > bandwidth that should be paid for with fees. What you're trying to do
> is
> > > replace a transaction without paying those fees, which is identical to
> > > what an
> > > attacker is trying to do, and thus any such scheme will be as
> vulnerable to
> > > attack as not having that protection in the first place.
> > >
> > > ...which does give you an out: maybe the attack isn't important enough
> to
> > > matter. :)
> > >
> >
> > Thanks, that makes sense.
> >
> > I still think it is worthwhile pursuing this proposed change in RBF
> policy
> > as it would seem that the current policy is problematic in practice today
> > where participants are just performing normal transactions and are not
> > trying to attack each other.
> But that's not a good argument: whether or not normal users are trying to
> attack each other has nothing to do with whether or not you're opening up
> an
> attack by relaxing anti-DoS protections.

I'm not suggesting removing the anti-DoS protections.  I'm suggesting that
replaced transaction require a fee increase of at least the min-fee-rate
times the size of all the transactions being ejected (in addition to the
other proposed requirements).

> Equally, how often are normal users who aren't attacking each other
> creating
> issues anyway? You can always have your wallet code just skip use of RBF
replacements in the event that someone does spend an unconfirmed output that
> you sent them; how often does this actually happen in practice?

Just ask rhavar.  It happens regularly.

Not many wallets let you spend unconfirmed outputs that you didn't create.

The problem is with institutional wallets sweeping incoming payments.  It
seems that in practice they are happy to sweep unconfirmed outputs.

Setting all of the above aside for a moment.  We need to understand that
rational miners are going to prefer to transactions with higher package fee
rates regardless of whatever your personal preferred RBF policy is.  If we
do not bring the RBF policy to alignment with what is economically
rational, then miners are going to change their own policies anyways,
probably all in slightly different ways.  It behooves everyone to develop a
reasonable standard RBF policy, that is still robust against possible DoS
vectors, and aligns with miner incentives, so that all participants know
what behaviour they can reasonably expect.  It is simply a bonus that this
change in RBF policy also partially mitigates the problem of pinned
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