From: Luke Dashjr <luke@dashjr.org>
To: bitcoin-dev@lists.linuxfoundation.org,
	Rusty Russell <rusty@rustcorp.com.au>
Date: Tue, 16 Jan 2018 04:15:54 +0000
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	<CAMZUoKn4noCEQR6eqf9hiZSMdk-3b8UHR1NrEFrKNoLSMzVjGQ@mail.gmail.com>
	<87zi5ehat5.fsf@rustcorp.com.au>
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Message-Id: <201801160415.55197.luke@dashjr.org>
Cc: Russell O'Connor <roconnor@blockstream.com>,
	Kalle Alm <kalle.alm@gmail.com>
Subject: Re: [bitcoin-dev] BIP 117 Feedback
Precedence: list

On Tuesday 16 January 2018 1:06:14 AM Rusty Russell via bitcoin-dev wrote:
> "Russell O'Connor" <roconnor@blockstream.io> 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