From: "David A. Harding" <dave@dtrt•org>
To: Peter Todd <pete@petertodd•org>,
Bitcoin Protocol Discussion
<bitcoin-dev@lists•linuxfoundation.org>
Cc: "lightning-dev@lists•linuxfoundation.org"
<lightning-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] OP_Expire and Coinbase-Like Behavior: Making HTLCs Safer by Letting Transactions Expire Safely
Date: Fri, 20 Oct 2023 22:58:32 -1000 [thread overview]
Message-ID: <d8227003b4a6065414d32a31a7020a93@dtrt.org> (raw)
In-Reply-To: <ZTMWrJ6DjxtslJBn@petertodd.org>
On 2023-10-20 14:09, Peter Todd via bitcoin-dev wrote:
> The basic problem here is after the HTLC-timeout path becomes
> spendable, the
> HTLC-preimage path remains spendable. That's bad, because in this case
> we want
> spending the HTLC-preimage - if possible - to have an urgency attached
> to it to
> ensure that it happens before the previous HTLC-timeout is mined.
>
> So, why can't we make the HTLC-preimage path expire?
If the goal is to ensure the HTLC-preimage should be mined before an
upstream HTLC-timeout becomes mineable, then I don't think a consensus
change is required. We can just make the HTLC-preimage claimable by
anyone some time after the HTLC-timeout becomes mineable.
For example, imagine that Alice offers Bob an HTLC with a timeout at
block t+200. Bob offers Carol an HTLC with a timeout at block t+100.
The Bob-Carol HTLC script looks like this:
If
# Does someone have the preimage?
Hash <digest> EqualVerify
If
# Carol has the preimage at any time
<Carol key> CheckSig
Else
# Anyone else has the preimage after t+150
<t+150> CLTV
EndIf
Else
# Bob is allowed a refund after t+100
<Bob key> CheckSigVerify
<t+100> CLTV
EndIf
In English:
- At any time, Carol can spend the output by releasing the preimage
- After t+100, Bob can spend the output
- After t+150, anyone with the preimage can spend the output
Let's consider this in the wider context of the forwarded payment
Alice->Bob->Carol:
- If Carol attempts to spend the output by releasing the preimage but
pays too low of a feerate to get it confirmed by block t+100, Bob can
spend the output in block t+101. He then has 99 blocks to settle
(revoke) the Alice-Bob HTLC offchain.
- If Carol releases the preimage to the network in general but prevents
Bob from using it (e.g. using a replacement cycling attack), anyone who
saw the preimage can take Carol's output at t+150 and, by doing so, will
put the preimage in the block chain where Bob will learn about it.
He'll then have 49 blocks to settle (revoke) the Alice-Bob HTLC
offchain.
- (All the normal cases when the HTLC is settled offchain, or where
onchain operations occur in a timely manner)
I think that adequately satisfies the concern about the effect on LN
from replacement cycling. Looking at potential complications:
- If all miners acted together[1], they are incentivized to not mine
Carol's preimage transaction before t+150 because its fees are less than
the HTLC value they can receive at t+150. I think this level of miner
centralization would result in a general failure for LN given that
miners could be any LN user's counterparty (or bribed by a user's
counterparty). E.g., stuff like this:
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2020-June/017997.html
- To allow anyone with the preimage to spend the output after t+150,
they need to know the script. For taproot, that means the t+150 tapleaf
script needs to follow a standard (e.g. a BOLT) and that any internal
merkle nodes needed to connect it to the taproot commitment need to be
shown in Carol's preimage transaction (or inferable from it or other
data).
- Classic RBF pinning of the t+150 transaction to prevent it from
confirming by block t+200 might be an issue. E.g., including it in a
400,000 weight low-feerate transaction.
- Full RBF might be required to ensure the t+150 transaction isn't sent
with a low feerate and no opt-in signal.
Deployment considerations:
- No changes are required to full nodes (no consensus change required)
- No changes are required to mining Bitcoin nodes[2]
- At least one well-connected Bitcoin relay node will need to be updated
to store preimages and related data, and to send the preimage claim
transactions. Data only needs to be kept for a rolling window of a few
thousand blocks for the LN case, bounding storage requirements. No
changes are required to other relaying Bitcoin nodes
- LN nodes will need to update to new HTLC scripts, but this should be
doable without closing/re-opening channels. Both anchor and non-anchor
channels can continue to be used
Compared to OP_EXPIRE:
- OP_EXPIRE requires consensus and policy changes; this does not
- OP_EXPIRE does not depend on special software; this depends on at
least one person running special software
Although this proposal is an alternative to Peter's proposal and is
primarily inspired by his idea, it's also a variation on a previous
suggestion of mine:
https://lists.linuxfoundation.org/pipermail/lightning-dev/2020-April/002664.html
-Dave
[1] Perhaps under block censorship threat from a mining majority or a
sub-majority performing selfish mining.
[2] Although miners may want to consider running code that allows them
to rewrite any malleable transactions to pay themselve
next prev parent reply other threads:[~2023-10-21 9:08 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-16 16:57 [bitcoin-dev] Full Disclosure: CVE-2023-40231 / CVE-2023-40232 / CVE-2023-40233 / CVE-2023-40234 "All your mempool are belong to us" Antoine Riard
2023-10-16 19:13 ` Peter Todd
2023-10-16 22:10 ` Matt Morehouse
2023-10-17 1:11 ` Antoine Riard
2023-10-20 10:47 ` Peter Todd
2023-10-20 11:18 ` Jochen Hoenicke
2023-10-16 22:51 ` Olaoluwa Osuntokun
2023-10-17 7:21 ` [bitcoin-dev] [Lightning-dev] " ziggie1984
2023-10-17 10:34 ` ZmnSCPxj
2023-10-17 18:34 ` Antoine Riard
2023-10-20 10:31 ` Peter Todd
2023-10-20 11:03 ` Peter Todd
2023-10-20 18:35 ` Matt Morehouse
2023-10-20 21:05 ` Matt Corallo
2023-10-21 0:15 ` Peter Todd
2023-10-21 1:03 ` Matt Corallo
2023-10-21 1:25 ` Peter Todd
2023-10-21 1:55 ` Matt Corallo
2023-10-21 2:43 ` Peter Todd
2023-10-23 16:09 ` Matt Corallo
2023-10-17 17:47 ` Antoine Riard
2023-10-17 18:47 ` Antoine Riard
2023-10-18 0:17 ` Matt Corallo
2023-10-18 2:57 ` Antoine Riard
2023-10-19 8:12 ` Bastien TEINTURIER
2023-10-19 16:23 ` Matt Morehouse
2023-10-19 17:22 ` Antoine Riard
2023-10-19 17:53 ` Matt Morehouse
2023-10-19 19:33 ` Antoine Riard
2023-10-21 0:18 ` Olaoluwa Osuntokun
2023-11-17 22:36 ` Antoine Riard
2023-10-19 18:02 ` Matt Corallo
2023-10-20 6:56 ` [bitcoin-dev] " Antoine Riard
2023-10-21 20:05 ` Antoine Riard
2023-10-27 0:43 ` Peter Todd
2023-11-02 4:46 ` Antoine Riard
2023-10-21 0:09 ` [bitcoin-dev] OP_Expire and Coinbase-Like Behavior: Making HTLCs Safer by Letting Transactions Expire Safely Peter Todd
2023-10-21 8:58 ` David A. Harding [this message]
2023-10-21 10:31 ` Peter Todd
2023-10-22 8:30 ` vjudeu
2023-10-23 11:10 ` [bitcoin-dev] [Lightning-dev] " ZmnSCPxj
2023-10-23 15:45 ` Peter Todd
2023-11-02 5:24 ` [bitcoin-dev] " Antoine Riard
2023-11-02 6:26 ` Peter Todd
2023-11-02 17:07 ` Matt Morehouse
2023-11-03 5:27 ` Antoine Riard
2023-11-03 5:25 ` Antoine Riard
2023-11-04 7:26 ` Peter Todd
2023-11-06 18:45 ` Antoine Riard
2023-11-07 11:11 ` [bitcoin-dev] [Lightning-dev] " ZmnSCPxj
2023-11-07 15:44 ` Antoine Riard
2023-11-08 0:51 ` [bitcoin-dev] " Peter Todd
2023-11-08 2:06 ` Peter Todd
2023-11-13 2:18 ` Antoine Riard
2023-11-14 19:50 ` Peter Todd
[not found] ` <CALZpt+H38cU9L8kq0mSYCDirzL39fxhdoz4pAPiS8dGJP8akKg@mail.gmail.com>
2023-11-15 17:53 ` [bitcoin-dev] Fwd: " Antoine Riard
2023-10-22 4:49 ` [bitcoin-dev] Full Disclosure: CVE-2023-40231 / CVE-2023-40232 / CVE-2023-40233 / CVE-2023-40234 "All your mempool are belong to us" Nadav Ivgi
2023-10-23 8:49 ` David A. Harding
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