I know that it is possible to create a 2-2 multsig using Taproot by combining both private keys into one public key and defining that as the key path spend. I also know that it is possible to use Tapscript to do the same thing with a script path spend using OP_CHECKSIGADD.

Is it also possible to use key aggregation in the script path spend, by just providing a public key and signature but doing the same key aggregation as in the key path spend? If so, would it ever make sense to use a "normal" OP_CHECKSIGADD operation in the case of multisig (not threshold signatures).


You are right. You could either use a leaf with a single aggregated key or a leaf with a more traditional multisig construction using OP_CHECKSIGADD.

The advantage of the aggregated key is its smaller input saving fees. The disadvantage is that MuSig2 is that it is an interactive protocol with multiple rounds which can be inconvenient if some of the signers are airgapped systems.

The OP_CHECKSIGADD construction on the other hand is a non-interactive construction, but reveals more information on-chain and costs more.

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