Ruben Somsen via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>writes:Hi Johnson,
The design considerations here seem similar to the ML discussion of
whether Graftroot should be optional [1].
While this seems fully compatible with eltoo, is there any other proposals require NOINPUT, and is adversely affected by either way of tagging?
As far as I can tell it should be compatible with Statechains [2],
since it pretty much mirrors Eltoo in setup.
My understanding is somewhat lacking, so perhaps I am missing the
mark, but it is not completely clear to me how this affects
fungibility if taproot gets added and the setup and trigger tx for
Eltoo get combined into a single transaction. Would the NOINPUT
spending condition be hidden inside the taproot commitment?
I'm not aware of a way to combine the setup and trigger transaction. Thetrigger transaction was introduced in order to delay the start of thetimeouts until a later time, to avoid having an absolute lifetime limitand having really huge timeout. If we were to combine the triggertransaction with the setup transaction (which is broadcast duringchannel creation), all of those timeouts would start counting downimmediately, and we could just skip the trigger transactionaltogether. It'd be more interesting to combine update and triggertransactions in a sort of cut-through combination, but that doesn't seempossible outside of Mimblewimble.Cheers,Christian
Correct me if I’m wrong.
For the sake of simplicity, in the following I assume BIP118, 143, and 141-P2WSH are used (i.e. no taproot). Also, I skipped all the possible optimisations.
1. A and B are going to setup a channel.
2. They create one setup tx, with a setup output of the following script: <s> CLTV DROP 2 Au Bu 2 CHECKMULTISIG. Do not sign
3. They create the update tx 0, spending the setup output with NOINPUT and locktime = s+1, to the update-0 output with the script:
IF 2 As0 Bs0 2 CHECKMULTISIG ELSE <s+1> CLTV DROP 2 Au Bu 2 CHECKMULTISIG ENDIF
4. They create the settlement tx 0, spending the update-0 output with As0 and Bs0 using BIP68 relative-locktime, with 2 settlement outputs
5. They sign the setup tx and let it confirm
6. To update, they create the update tx 1, spending the setup output with NOINPUT and locktime = s+2, to the update-1 output with the script:
IF 2 As1 Bs1 2 CHECKMULTISIG ELSE <s+2> CLTV DROP 2 Au Bu 2 CHECKMULTISIG ENDIF
and create the settlement tx 1, spending the update-1 output with As1 and Bs1 using relative-locktime, with 2 settlement outputs
7. To close the channel, broadcast update tx 1. Wait for several confirmations. And broadcast settlement-tx-1