Re: [bitcoindev] Prohibit Merkle Internal Node Preimages That Encode Minimal 64-Byte Transactions

[jeremy <jeremy.l.rubin@gmail.com>]

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Antoine,

Rejecting nodes with any valid tx in path, without this rule, is 
problematic, because it _can_ be possible for an attacking miner to 
engineer that scenario by grinding one TXID leaf to mask a subtree, which 
could have major consequences. Third party malleability vulnerability to 
deposit / withdrawal masking is a serious bug. Worth thinking that through 
very carefully before recommending these mitigations. Do you have an 
end-to-end working example of such a mitigation that doesn't have these 
issues?

> This is incorrect for any bridge, wallet, or deposit system that does not 
receive funds to a script that either burns the funds or that anyone can 
spend.

The problem is that from the perspective of a wide variety of layer 2 
protocols, you actually do want to be able to simply close out a UTXO and 
prove a UTXO is spent.

In the current L2 protocol design space, value doesn't always flow directly 
along the output,  the UTXO may be being used as a connector input, and the 
spend of that output may be making a different output available after a 
timeout and excluding an alternative spend.

Best,

Jeremy

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