Subject: Re: [bitcoin-dev] BIP 117 Feedback

From: Luke Dashjr <[email-masked]>
Date: Tue, 16 Jan 2018 04:15:54 +0000

On Tuesday 16 January 2018 1:06:14 AM Rusty Russell via bitcoin-dev wrote:
> "Russell O'Connor" <[email-masked]> writes:
> > However, if I understand correctly, the situation for BIP 117 is entirely
> > different.  As far as I understand there is currently no restrictions
> > about terminating a v0 witness program with a non-empty alt-stack, and
> > there are no restrictions on leaving non-canonical boolean values on the
> > main stack.
> 
> BIP-141: "The script must not fail, and result in exactly a single TRUE
> on the stack."  And it has long been non-standard for P2SH scripts to
> not do the same (don't know exactly when).

This doesn't affect the alt-stack (it's a completely separate stack).

> The rule AFAICT is "standard transactions must still work".  This was
> violated with low-S, but the transformation was arguably trivial.
> 
> OTOH, use of altstack is completely standard, though in practice it's
> unused and so only a theoretical concern.

I'm not aware of a single standard/BIP that uses the altstack at all.

Luke