From: ZmnSCPxj <ZmnSCPxj@protonmail•com>
To: Anthony Towns <aj@erisian•com.au>
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: Fri, 22 Mar 2019 01:59:14 +0000 [thread overview]
Message-ID: <ITq8Tl8XaPXWzqs0F7yY3POHtysci93evnyLteDL9bYRxjjgJbTV_d-xCn_j5AZApGqCIBQ0p6UH8S-bD_n8hm1IMYS98ukpJkO4PGDXsuQ=@protonmail.com> (raw)
In-Reply-To: <20190321115522.lf7z6xb224lqqfla@erisian.com.au>
Good morning aj,
>
> If you are committing to the script code, though, then each settlement
> sig is already only usable with the corresponding update tx, so you
> don't need to roll the keys. But you do need to make it so that the
> update sig requires the CLTV; one way to do that is using codeseparator
> to distinguish between the two cases.
>
> > Also, I cannot understand `OP_CODESEPARATOR`, please no.
>
> If codeseparator is too scary, you could probably also just always
> require the locktime (ie for settlmenet txs as well as update txs), ie:
>
> OP_CHECKLOCKTIMEVERIFY OP_DROP
> <muSig(A_u,B_u)> OP_CHECKDLSVERIFY <Q> OP_CHECKDLS
>
> and have update txs set their timelock; and settlement txs set a absolute
> timelock, relative timelock via sequence, and commit to the script code.
>
> (Note that both those approaches (with and without codesep) assume there's
> some flag that allows you to commit to the scriptcode even though you're
> not committing to your input tx (and possibly not committing to the
> scriptpubkey). BIP118 doesn't have that flexibility, so the A_s_i and
> B_s_i key rolling is necessary)
I think the issue I have here is the lack of `OP_CSV` in the settlement branch.
Consider a channel with offchain transactions update-1, settlement-1, update-2, and settlement-2.
If update-1 is placed onchain, update-1 is also immediately spendable by settlement-1.
But settlement-1 cannot be spent by update-2 and thus the invalidation of older state fails.
The `OP_CSV` in the settlement branch of the update transaction outputs exists to allow later update transactions have higher priority over settlement transactions.
To ensure that a settlement signature can only take the settlement branch, we need a distinct public key for the branch, so at least `A_s` and `B_s` without rolling them for each `i`, if we use `nLockTime` on the settlement transactions and enforce it with `OP_CHECKLOCKTIMEVERIFY`.
It might be possible to do this with `OP_CODESEPARATOR`, but we do need the `OP_CSV` in the settlement branch.
Regards,
ZmnSCPxj
next prev parent reply other threads:[~2019-03-22 1:59 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
2019-03-21 10:05 ` ZmnSCPxj
2019-03-21 11:55 ` Anthony Towns
2019-03-22 1:59 ` ZmnSCPxj [this message]
2019-03-22 2:58 ` Anthony Towns
2019-03-22 7:46 ` ZmnSCPxj
2019-03-22 4:23 ` Johnson Lau
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