Signing Custom Tapscript Leaves with walletprocesspsbt Using Bitcoind

As a wallet user, you are probably familiar with the intricacies of managing multisig scripts in Bitcoin. In this article, we will explore how to sign custom Tapscript leaves using the walletprocesspsbt RPC endpoint from a Bitcoin node.

Understanding Multisig Scripts and Tapscripts

Multisig scripts are used in taproot wallets to allow multiple parties to spend funds without revealing their private keys. Each multisig script is defined as a tapscript, which is a sequence of transactions that specifies how to spend the funds. In your case, you have three different script paths for each multisig.

Tapscripts can be compiled and optimized by Bitcoin Core (the default wallet software) into scripts that can be used to sign custom leaves. A “leaf” in this context refers to a single transaction output that is part of a multisig script.

Walletprocesspsbt RPC Endpoint

The walletprocesspsbt endpoint is a powerful tool provided by Bitcoind, the official Bitcoin node software. It allows you to process payment requests and generate multiple transaction outputs from your wallet’s private keys. You can use this endpoint to sign custom leaves using tapscripts.

To get started, make sure you have Bitcoin Core installed on your system and running. Next, navigate to your wallet’s configuration directory:

cd ~/.bitcoincorewallet

Next, edit the settings.conf file (usually located at ~/.bitcoincorewallet/settings.conf) to add the following line:

rpc-process-pssbt = true

This tells Bitcoin Core to use the walletprocesspsbt endpoint.

Signing Custom Leaves with Tapscripts

Now that you have enabled the walletprocesspsbt endpoint, you can sign custom leaves using tapscripts. Here is an example of how to compile a tapscript for path 1 of the multisig script:

taproot-compile -scriptpath /path/to/script1.txb --outputpath /path/to/output1.p2sh

Replace /path/to/script1.txb with the actual file containing your multisig script and /path/to/output1.p2sh with the desired output file format (e.g. p2sh).

Once you have compiled the tapscript, you can use the walletprocesspsbt endpoint to sign it using your private key:

bitcoincorewallet --rpc-process-pssbt p2sh --path /path/to/output1.p2sh --privatekey 

This will generate a single transaction output containing all of the multisig script output.

Example Use Case

Let’s say you have three different multisig scripts defined as tapscripts and each has a different script path. You can compile them using taproot-compile and then use the walletprocesspsbt endpoint to sign custom leaves for each script:

Compile multisig scripts 1-3
taproot-compile -scriptpath /path/to/script1.txb --outputpath /path/to/output1.p2sh
taproot-compile -scriptpath /path/to/script2.txb --outputpath /path/to/output2.p2sh
taproot-compile -scriptpath /path/to/script3.txb --outputpath /path/to/output3.p2sh

Sign custom leaves for each multisig script
bitcoincorewallet --rpc-process-pssbt p2sh --path /path/to/output1.p2sh --privatekey  \
--scriptpath /path/to/script1.txb \
--script 0x1234567890abcdef \
--output /path/to/output1

This will generate three custom transaction outputs containing all the multisig script outputs for each script.

In summary, you can sign custom tapscripts using walletprocesspsbt and generate multiple transaction outputs from your wallet’s private keys. This allows you to easily manage complex multisig scripts in taproot wallets.

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