Date: Tue, 26 Apr 2022 03:00:12 +1000
From: Anthony Towns <aj@erisian.com.au>
To: Keagan McClelland <keagan.mcclelland@gmail.com>,
 Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
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Subject: Re: [bitcoin-dev] Speedy Trial
Precedence: list

On Mon, Apr 25, 2022 at 10:11:45AM -0600, Keagan McClelland via bitcoin-dev wrote:
> > Under *any* other circumstance, when they're used to activate a bad soft
> > fork, speedy trial and bip8 are the same. If a resistance method works
> > against bip8, it works against speedy trial; if it fails against speedy
> > trial, it fails against bip8.
> IIRC one essential difference between ST (which is a variant of BIP9) and
> BIP8 is that since there is no mandatory signaling during the lockin
> period, 

BIP8 doesn't have mandatory signaling during the lockin period, it has
semi-mandatory [0] signalling during the must_signal period. 

> you can't do a counter soft fork as easily.

The "counter" for bip8 activation is to reject any block during either
the started or must_signal phases that would meet the threshold. In that
case someone running bip8 might see blocks:

  [elapsed=2010, count=1813, signal=yes]
  [elapsed=2011, count=1813, signal=no]
  [elapsed=2012, count=1814, signal=yes]
  [elapsed=2013, count=1815, signal=yes, will-lockin!]
  [elapsed=2014, count=1816, signal=yes]
  [elapsed=2015, count=1816, signal=no]
  [elapsed=2016, count=1816, signal=no]
  [locked in!]

But running software to reject the soft fork, you would reject the
elapsed=2013 block, and any blocks that build on it. You would wait for
someone else to mine a chain that looked like:

  [elapsed=2013, count=1814, signal=no]
  [elapsed=2014, count=1814, signal=no]
  [elapsed=2015, count=1814, signal=no]
  [elapsed=2016, count=1814, signal=no]
  [failed!]

That approach works *exactly* the same with speedy trial.

Jeremy's written code that does exactly this using the getdeploymentinfo
rpc to check the deployment status, and the invalidateblock rpc to
reject a block. See: https://github.com/JeremyRubin/forkd

The difference to bip8 with lot=true is that nodes running speedy trial
will reorg to follow the resisting chain if it has the most work. bip8
with lot=true nodes will not reorg to a failing chain, potentially
creating an ongoing chain split, unless one group or the other gives up,
and changes their software.

Cheers,
aj

[0] Semi-mandatory in that only "threshold" blocks must signal, so if
    only 4% or 9% of miners aren't signalling and the threshold is set
    at 95% or 90%, no blocks will be orphaned.