Subject: Re: [bitcoin-dev] Safer NOINPUT with output tagging

From: ZmnSCPxj <[email-masked]>
Date: Fri, 01 Feb 2019 09:36:50 +0000

Good morning aj,

I certainly agree.
I hope that PSBT support becomes much, much, much more widespread.

Regards,
ZmnSCPxj

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‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Thursday, January 31, 2019 2:04 PM, Anthony Towns <[email-masked]> wrote:

> On Mon, Dec 24, 2018 at 11:47:38AM +0000, ZmnSCPxj via bitcoin-dev wrote:
>
> > A boutique protocol would reduce the number of existing onchain wallets that could be integrated in such UI.
>
> Seems like PSBT would be a sufficient protocol:
>
> 0) lightning node generates a PSBT for a new channel,
> with no inputs and a single output of the 2-of-2 address
>
> 1.  wallet funds the PSBT but doesn't sign it, adding a change address
>     if necessary, and could combine with other tx's bustapay style
>
> 2.  lightning determines txid from PSBT, and creates update/settlement
>     tx's for funding tx so funds can be recovered
>
> 3.  wallet signs and publishes the PSBT
> 4.  lightning sees tx on chain and channel is open
>
>     That's a bit more convoluted than "(0) lightning generates an address and
>     value, and creates NOINPUT update/settlement tx's for that address/value;
>     (1) wallet funds address to exactly that value; (2) lightning monitors
>     blockchain for payment to that address" of course.
>
>     But it avoids letting users get into the habit of passing NOINPUT
>     addresses around, or the risk of a user typo'ing the value and losing
>     money immediately, and it has the benefit that the wallet can tweak the
>     value if (eg) that avoids a change address or enhances privacy (iirc,
>     c-lightning tweaks payment values for that reason). If the channel's
>     closed cooperatively, it also avoids ever needing to publish a NOINPUT
>     sig (or NOINPUT tagged output).
>
>     Does that seem a fair trade off?
>
>     Cheers,
>     aj
>