[Bitcoin-development] replace-by-fee v0.10.0rc4

Eric Lombrozo elombrozo at gmail.com
Sun Feb 22 11:41:26 UTC 2015

It seems to me we're confusing two completely different motivations for
double-spending. One is the ability to replace a fee, the other is the
ability to replace outputs.

If the double-spend were to merely add or remove inputs (but keep at least
one input in common, of course), it seems fairly safe to assume it's the
former, a genuine fee replacement. Even allowing for things like coinjoin,
none of the payees would really care either way.

Conversely, if at least one of the inputs were kept but none of the outputs
were, we can be confident it's the the latter.

It is possible to build a wallet that always does the former when doing fee
replacement by using another transaction to create an output with exactly
the additional desired fee.

If we can clearly distinguish these two cases then the fee replacement case
can be handled by relaying both and letting miners pick one or the other
while the output replacement case could be handled by rewarding everything
to a miner (essentially all outputs are voided...made unredeemable...and
all inputs are added to coinbase) if the miner includes the two conflicting
transactions in the same block.

Wouldn't this essentially solve the problem?

- Eric Lombrozo
On Feb 21, 2015 8:09 PM, "Jeff Garzik" <jgarzik at bitpay.com> wrote:

> On Sat, Feb 21, 2015 at 10:25 PM, Jorge Timón <jtimon at jtimon.cc> wrote:
> > On Sat, Feb 21, 2015 at 11:47 PM, Jeff Garzik <jgarzik at bitpay.com>
> wrote:
> >> This isn't some theoretical exercise.  Like it or not many use
> >> insecure 0-conf transactions for rapid payments.  Deploying something
> >> that makes 0-conf transactions unusable would have a wide, negative
> >> impact on present day bitcoin payments, thus "scorched earth"
> > And maybe by maintaining first seen policies we're harming the system
> > in the long term by encouraging people to widely deploy systems based
> > on extremely weak assumptions.
> Lacking a coded, reviewed alternative, that's only a platitude.
> Widely used 0-conf payments are where we're at today.  Simply ceasing
> the "maintaining [of] first seen policies" alone is simply not a
> realistic option.  The negative impact to today's userbase would be
> huge.
> Instant payments need a security upgrade, yes.
> --
> Jeff Garzik
> Bitcoin core developer and open source evangelist
> BitPay, Inc.      https://bitpay.com/
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