[Bitcoin-development] BIP - Selector Script

Tier Nolan tier.nolan at gmail.com
Fri Apr 25 20:02:41 UTC 2014

On Fri, Apr 25, 2014 at 8:17 PM, Luke-Jr <luke at dashjr.org> wrote:

> I believe you meant to link here instead?
>     https://github.com/TierNolan/bips/blob/bip4x/bip-0046.mediawiki
> Yeah, sorry.

> This looks reasonable from a brief skim over, but does not define any use
> cases (it mentions "necessary for atomic cross chain transfers", but does
> not
> explain how it is useful for that - perhaps that belongs in another BIP you
> haven't written yet, though).

One use case should be enough.  The atomic cross chain proposal has been
discussed for a while.  It feels like bitcoin works on an "ask permission
first" basis.

It always stalls at the fact that non-standard transactions are hard to get
confirmed on other coins.  It is hard to find pools on other coins which
have weaker isStandard() checks.  The timeouts have to be set so that they
are long enough to guarantee that transactions are accepted before they

A testnet to testnet transfer is the best that would be possible at the

I don't think the cross chain system needs a BIP (except to justify this

If cross chain transfer become popular, then it would be useful to ensure
that clients are interoperable, but first things first.  If the
transactions aren't accepted in any chains, then everything stalls.

Secure transfers require that the malleability issue is fixed, but that is
a separate issue.  I am assuming that will be fixed at some point in the
future, since micro-payment channels also requires that it is fixed.

> IMO, it should also require P2SH.

It could be restricted to only P2SH, I don't think there would be a loss in
doing that.

Personally, I would make it so that P2SH is mandatory after a certain
time.  It makes distributed verification of the block chain easier.
Everything needed to verify a script is present in the transaction (except
that the output actually exists).

A soft fork that expands P2SH functionality would be even better, but I
would rather not let the best be the enemy of the good.

> Luke
> On Friday, April 25, 2014 6:49:35 PM Tier Nolan wrote:
> > This is a BIP to allow the spender to choose one of multiple standard
> > scripts to use for spending the output.
> >
> > https://github.com/TierNolan/bips/blob/bip4x/bip-0045.mediawiki
> >
> > This is required as part of the atomic cross chain transfer protocol.  It
> > is required so that outputs can be retrieved, if the process ends before
> > being committed.
> >
> > https://bitcointalk.org/index.php?topic=193281.msg2224949#msg2224949
> >
> > The script allows multiple standard scripts to be included in the
> > scriptPubKey.
> >
> > When redeeming the script the spender indicates which of the standard
> > scripts to use.
> >
> > Only one standard script is actually executed, so the only cost is the
> > extra storage required.
> >
> > A more ambitious change would be a soft fork like P2SH, except the
> spender
> > is allowed to select from multiple hashes.  Effectively, it would be
> > "Multi-P2SH".
> >
> > This gets much of the benefits of MAST, but it requires a formal soft
> fork
> > to implement.
> >
> > If there is agreement, I can code up the reference implementation as a
> PR.
> > The multi-P2SH might actually be easier.
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