Re: [Bitcoin-development] F2Pool has enabled full replace-by-fee

[Jeff Garzik <jgarzik@bitpay.com>]

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Yes, FSS RBF is far better.


On Fri, Jun 19, 2015 at 6:52 AM, Chun Wang <1240902@gmail.com> wrote:

> Before F2Pool's launch, I performed probably the only successful
> bitcoin double spend in the March 2013 fork without any mining power.
> [ https://bitcointalk.org/index.php?topic=152348.0 ] I know how bad
> the full RBF is. We are going to switch to FSS RBF in a few hours.
> Sorry.
>
> On Fri, Jun 19, 2015 at 9:44 PM, Peter Todd <pete@petertodd.org> wrote:
> > On Fri, Jun 19, 2015 at 09:33:05AM -0400, Stephen Morse wrote:
> >> It is disappointing that F2Pool would enable full RBF when the safe
> >> alternative, first-seen-safe RBF, is also available, especially since
> the
> >> fees they would gain by supporting full RBF over FSS RBF would likely be
> >> negligible. Did they consider using FSS RBF instead?
> >
> > Specifically the following is what I told them:
> >
> >> We are
> >> interested in the replace-by-fee patch, but I am not following the
> >> development closely, more background info is needed, like what the
> >> difference between standard and zeroconf versions? Thanks.
> >
> > Great!
> >
> > Basically both let you replace one transaction with another that pays a
> > higher fee. First-seen-safe replace-by-fee adds the additional criteria
> > that all outputs of the old transaction still need to be paid by the new
> > transaction, with >= as many Bitcoins. Basically, it makes sure that if
> > someone was paid by tx1, then tx2 will still pay them.
> >
> > I've written about how wallets can use RBF and FSS-RBF to more
> > efficiently use the blockchain on the bitcoin-development mailing list:
> >
> >
> http://www.mail-archive.com/bitcoin-development@lists.sourceforge.net/msg07813.html
> >
> http://www.mail-archive.com/bitcoin-development@lists.sourceforge.net/msg07829.html
> >
> > Basically, for the purpose of increasing fees, RBF is something like %50
> > cheaper than CPFP, and FSS-RBF is something like %25 cheaper.
> >
> > In addition, for ease of implementation, my new FSS-RBF has a number of
> > other restrictions. For instance, you can't replace multiple
> > transactions with one, you can't replace a transaction whose outputs
> > have already been spent, you can't replace a transaction with one that
> > spends additional unconfirmed inputs, etc. These restrictions aren't
> > "set in stone", but they do make the code simpler and less likely to
> > have bugs.
> >
> > In comparison my previous standard RBF patch can replace multiple
> > transactions with one, can replace long chains of transactions, etc.
> > It's willing to do more computation before deciding if a transaction
> > should be replaced, with more complex logic; it probably has a higher
> > chance of having a bug or DoS attack.
> >
> > You've probably seen the huge controversy around zeroconf with regard to
> > standard replace-by-fee. While FSS RBF doesn't make zeroconf any safer,
> > it also doesn't make it any more dangerous, so politically with regard
> > to zeroconf it makes no difference. You *can* still use it doublespend
> > by taking advantage of how different transactions are accepted
> > differently, but that's true of *every* change we've ever made to
> > Bitcoin Core - by upgrading to v0.10 from v0.9 you've also "broken"
> > zeroconf in the same way.
> >
> >
> > Having said that... honestly, zeroconf is pretty broken already. Only
> > with pretty heroic measures like connecting to a significant fraction of
> > the Bitcoin network at once, as well as connecting to getblocktemplate
> > supporting miners to figure out what transactions are being mined, are
> > services having any hope of avoiding getting ripped off. For the average
> > user their wallets do a terrible job of showing whether or not an
> > unconfirmed transaction will go through. For example, Schildbach's
> > Bitcoin wallet for Android has no code at all to detect double-spends
> > until they get mined, and I've been able to trick it into showing
> > completely invalid transactions. In fact, currently Bitcoin XT will
> > relay invalid transactions that are doublepsends, and Schildbach's
> > wallet displays them as valid, unconfirmed, payments. It's really no
> > surprise to me that nearly no-one in the Bitcoin ecosystem accepts
> > unconfirmed transactions without some kind of protection that doesn't
> > rely on first-seen-safe mempool behavior. For instance, many ATM's these
> > days know who their customers are due to AML requirements, so while you
> > can deposit Bitcoins and get your funds instantly, the protection for
> > the ATM operator is that they can go to the police if you rip them off;
> > I've spoken to ATM operators who didn't do this who've lost hundreds or
> > even thousands of dollars before giving up on zeroconf.
> >
> > My big worry with zeroconf is a service like Coinbase or Shapeshift
> > coming to rely on it, and then attempting to secure it by gaining
> > control of a majority of hashing power. For instance, if Coinbase had
> > contracts with 80% of the Bitcoin hashing power to guarantee their
> > transactions would get mined, but 20% of the hashing power didn't sign
> > up, then the only way to guarantee their transactions could be for the
> > 80% to not build on blocks containing doublespends by the 20%. There's
> > no way in a decentralized network to come to consensus about what
> > transactions are or are not valid without mining itself, so you could
> > end up in a situation where unless you're part of one of the big pools
> > you can't reliably mine at all because your blocks may get rejected for
> > containing doublespends.
> >
> > One of my goal with standard replace-by-fee is to prevent this scenario
> > by forcing merchants and others to implement ways of accepting zeroconf
> > transactions safely that work in a decentralized environment regardless
> > of what miners do; we have a stronger and safer Bitcoin ecosystem if
> > we're relying on math rather than trust to secure our zeroconf
> > transactions. We're also being more honest to users, who right now often
> > have the very wrong impression that unconfirmed transactions are safe to
> > accept - this does get people ripped off all too often!
> >
> >
> > Anyway, sorry for the rant! FWIW I updated my FSS-RBF patch and am
> > waiting to get some feedback:
> >
> >     https://github.com/bitcoin/bitcoin/pull/6176
> >
> > Suhas Daftuar did find a pretty serious bug in it, now fixed. I'm
> > working on porting it to v0.10.2, and once that's done I'm going to put
> > up a bounty for anyone who can find a DoS attack in the patch. If no-one
> > claims the bounty after a week or two I think I'll start feeling
> > confident about using it in production.
> >
> >
> > --
> > 'peter'[:-1]@petertodd.org
> > 000000000000000003188926be14e5fbe2f8f9c63c9fb8e2ba4b14ab04f1c9ab
> >
> >
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-- 
Jeff Garzik
Bitcoin core developer and open source evangelist
BitPay, Inc.      https://bitpay.com/

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