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From: Anthony Towns <aj@erisian•com.au>
To: ZmnSCPxj <ZmnSCPxj@protonmail•com>
Cc: "bitcoin-dev@lists•linuxfoundation.org"
	<bitcoin-dev@lists•linuxfoundation.org>,
	"lightning-dev@lists•linuxfoundation.org"
	<lightning-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] [Lightning-dev] More thoughts on NOINPUT safety
Date: Thu, 21 Mar 2019 19:06:14 +1000	[thread overview]
Message-ID: <20190321090614.7ir64g2ehn3pz2cb@erisian.com.au> (raw)
In-Reply-To: <isp2OcX23r-Tfl-WSbybuKnppjVlZV52AM1GGEaQd8uHlkliikUBvK49WOnzgaxOjDuOCNdu6CsmHt6kfK0z_FRrOgYAYWrWaDniZA3EEZQ=@protonmail.com>

On Wed, Mar 20, 2019 at 08:07:00AM +0000, ZmnSCPxj via Lightning-dev wrote:
> Re-reading again, I think perhaps I was massively confused by this:
> > that commits to the input. In that case, you could do eltoo with a
> > script like either:
> > <A> CHECKSIGVERIFY <B> CHECKSIG
> > or <P> CHECKSIGVERIFY <Q> CHECKSIG
> Do you mean that *either* of the above two scripts is OK, *or* do you mean they are alternatives within a single MAST or `OP_IF`?

I meant "either of the two scripts is okay".

> In the blob sent to Watchtower, A (or B) includes the `SIGHASH_NOINPUT` as well as the `q` private key.
> Would it be safe for Watchtower to know that?

I think so. From Alice/Bob's point-of-view, the NOINPUT sig ensures they
control their money; and from the network's point-of-view (or at least
that part of the network that thinks NOINPUT is unsafe) the Q private
key being shared makes the tx no worse than a 1-of-n multisig setup,
which has to be dealt with anyway.

> Then each update transaction pays out to:
>     OP_IF
>         <csv_delta> OP_CSV OP_DROP
>         <muSig(A_si,B_si)> OP_CHECKSIGVERIFY <Q> OP_CHECKSIG
>     OP_ELSE
>         <i> OP_CHECKLOCKTIMEVERIFY OP_DROP
>         <muSig(A_u,B_u)> OP_CHECKSIGVERIFY <Q> OP_CHECKSIG
>     OP_ENDIF

Yeah.

I think we could potentially make that shorter still:

   IF OP_CODESEPARATOR <i> OP_CHECKLOCKTIMEVERIFY OP_DROP ENDIF
   <muSig(A_u,B_u)> OP_CHECKDLSVERIFY <Q> OP_CHECKDLS

Signing with NOINPUT,NOSCRIPT and codeseparatorpos=1 enforces CLTV
and allows binding to any prior update tx -- so works for an update tx
spending previous update txs; while signing with codeseparatorpos=-1
and NOINPUT but committing to the script code and nSequence (for the
CSV delay) allows binding to only that update tx -- so works for the
settlement tx. That's two pubkeys, two sigs, and the taproot point
reveal.

Cheers,
aj



  parent reply	other threads:[~2019-03-21  9:06 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-13  1:41 [bitcoin-dev] " Anthony Towns
2019-03-13  6:41 ` [bitcoin-dev] [Lightning-dev] " ZmnSCPxj
2019-03-13 11:10   ` Anthony Towns
2019-03-14  5:22     ` ZmnSCPxj
2019-03-14  7:24       ` Anthony Towns
2019-03-14  7:55         ` ZmnSCPxj
2019-03-14 12:00         ` Christian Decker
2019-03-20  0:22 ` Rusty Russell
2019-03-20  3:33   ` Rusty Russell
2019-03-20  7:38     ` ZmnSCPxj
2019-03-20  8:07       ` ZmnSCPxj
2019-03-21  8:37         ` Johnson Lau
2019-03-21  9:06         ` Anthony Towns [this message]
2019-03-21 10:05           ` ZmnSCPxj
2019-03-21 11:55             ` Anthony Towns
2019-03-22  1:59               ` ZmnSCPxj
2019-03-22  2:58                 ` Anthony Towns
2019-03-22  7:46                   ` ZmnSCPxj
2019-03-22  4:23                 ` Johnson Lau

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