Ethereum: What is the script assembly and execution in P2TR spend (spend from Taproot)

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Ethereum: Understanding Script Assembly and Execution in P2TR Spend (spend from Taproot)

As you have gained a solid understanding of Bitcoin’s script assembly and execution, particularly with regards to Taproot (P2PKH) payments, we’ll dive deeper into the specifics of script assembly for P2TR spends (spends from Taproot).

What is P2TR Spend?

A P2TR spend involves spending bitcoins from a public address that was previously spent using Taproot (P2PKH). In other words, you’re re-spending the same bitcoins that were originally spent in a taproot transaction. This allows for more complex and secure payments without the need to create new scripts or derive new addresses.

Script Assembly for P2TR Spends

To execute a P2TR spend, we must first understand the script assembly process used by Ethereum’s Ropsten testnet. The key components of an Ethereum script are:

• Input Scripts

  : These define how the input amount should be spent from.

• Output Scripts: These determine what is being sent to the recipient and any additional fees or relayers.

For a P2TR spend, we have two primary input scripts: one for the original Taproot transaction and another that creates a new script for the re-spent bitcoins.

Taproot Script Input

The original taproot transaction has an input script of type scriptPubKey, which is a key-value pair representing the public address to be spent. This input script is used as the first input in our P2TR spend.

0x1... (public address)

Taproot Script Output

The re-spent Taproot transaction has an output script that defines how the amount should be sent. The scriptPubKey field of this output script contains the public address to which the re-spent bitcoins are being sent.

0x1... (public address)

Script Assembly for P2TR

Now, let’s combine these two scripts to create a P2TR spend that re-sends the same Taproot transaction. We’ll use Solidity, a popular programming language for Ethereum smart contracts, to implement this assembly.

“`solidity

pragma solidity ^0.8.0;

contract TaprootSpend {

// Input script from original taproot transaction

address public owner;

// Function to execute P2TR spend

function executeP2TR(uint amount) public {

// Create a new input script for the re-spent bitcoins

address public recipientAddress;

uint256 public outputAmount = 0;

// Define the output script using the output script of the original taproot transaction

function getOutputScript() internal returns (address, uint256) {

return address(0x1…, owner), amount;

}

// Use the re-spent Taproot transaction to calculate the recipient address and amount

address public newAddress;

uint256 public newAmount = 0;

// Define a function that takes in the output script of the original taproot transaction and calculates the corresponding inputs for the re-spent bitcoins

function getNewInputs() internal returns (address[] memory, uint256[]) {

// Calculate the recipient address using the public address from the original Taproot transaction

address[] memory recipients = newAddress;

// Calculate the output amount in wei

uint256[] memory outputs = newuint256(recipients.