On Wed, Apr 11, 2018 at 02:22:42PM +0900, Karl-Johan Alm via bitcoin-dev wrote:
> Clarification on one part below:
> 
> On Wed, Apr 11, 2018 at 2:21 PM, Karl-Johan Alm
> <karljohan-alm@garage.co.jp> wrote:
> > On Wed, Apr 11, 2018 at 5:29 AM, Maksim Solovjov via bitcoin-dev
> > <bitcoin-dev@lists.linuxfoundation.org> wrote:
> >> 1. What does it mean for a transaction ( with 0 confirmations ) to be
> >> trusted or not?
> >
> > It is trusted if (1) it is final (i.e. it can't be replaced), (2) it
> > is not in a block that was reorged out (negative confirmation count),
> > (3) the 'spend zero conf change' option is set, (4) it is in the
> > mempool, and (5) all inputs are from us.
> 
> "can't be replaced" here means it cannot be replaced through
> conventional means. It is always possible to replace a transaction
> that has not yet been confirmed, e.g. by asking a miner to mine a
> conflicting transaction directly.

Or via full replace-by-fee, which appears to be used by a significant minority
of miners:

https://github.com/petertodd/bitcoin/tree/replace-by-fee-v0.16.0

In practice transaction replacement by the sender for any transaction is very
easy.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org