Date: Mon, 30 Sep 2019 23:28:43 +0000
To: ZmnSCPxj <ZmnSCPxj@protonmail.com>,
	Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
From: ZmnSCPxj <ZmnSCPxj@protonmail.com>
Reply-To: ZmnSCPxj <ZmnSCPxj@protonmail.com>
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Cc: "lightning-dev@lists.linuxfoundation.org"
	<lightning-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Continuing the discussion about noinput /
	anyprevout
Precedence: list

Good morning list,

To elucidate further ---

Suppose rather than `SIGHASH_NOINPUT`, we created a new opcode, `OP_CHECKSI=
G_WITHOUT_INPUT`.

This new opcode ignores any `SIGHASH` flags, if present, on a signature, bu=
t instead hashes the current transaction without the input references, then=
 checks that hash to the signature.

This is equivalent to `SIGHASH_NOINPUT`.

Yet as an opcode, it would be possible to embed in a Taproot script.

For example, a Decker-Russell-Osuntokun would have an internal Taproot poin=
t be a 2-of-2, then have a script `OP_1 OP_CHECKSIG_WITHOUT_INPUT`.
Unilateral closes would expose the hidden script, but cooperative closes wo=
uld use the 2-of-2 directly.

Of note, is that any special SCRIPT would already be supportable by Taproot=
.
This includes SCRIPTs that may potentially lose funds for the user.
Yet such SCRIPTs are already targetable by a Taproot address.

If we are so concerned about `SIGHASH_NOINPUT` abuse, why are we not so con=
cerned about Taproot abuse?

Regards,
ZmnSCPxj