Allow omitting previousTx for taproot splices
#3143
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When splicing a taproot channel, both participants will provide a signature for a segwit v1 input: this signature will cover every spent `txOut`, including their amount and script. This ensures that attackers cannot reuse a signature while replacing a segwit input with a non-segwit input, which could be used to steal funds. A side-effect of this change in signature behavior is that we don't need to provide the entire previous transaction when both channel participants sign a taproot input. For simplicity, we only allow this simplification when splicing taproot channels for now. We can also allow channel creation based on swap-in-potentiam, which also uses musig2 and has the same non-malleability guarantee (on feature branches for phoenix users).
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sstone
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Aug 25, 2025
eclair-core/src/main/scala/fr/acinq/eclair/channel/fund/InteractiveTxBuilder.scala
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sstone
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Aug 25, 2025
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When splicing a taproot channel, both participants will provide a signature for a segwit v1 input: this signature will cover every spent
txOut, including their amount and script. This ensures that attackers cannot reuse a signature while replacing a segwit input with a non-segwit input, which could be used to steal funds.A side-effect of this change in signature behavior is that we don't need to provide the entire previous transaction when both channel participants sign a taproot input. For simplicity, we only allow this simplification when splicing taproot channels for now. We can also allow channel creation based on swap-in-potentiam, which also uses musig2 and has the same non-malleability guarantee (on feature branches for phoenix users).
See https://delvingbitcoin.org/t/malleability-issues-when-creating-shared-transactions-with-segwit-v0/497 for more details.