Exercise 3: Hard

P2PK ScriptPubKey to ASM Converter

In this exercise, you'll implement a function to convert a P2PK (Pay-to-Public-Key) ScriptPubKey from its hexadecimal representation to ASM format.

Implement the decodeP2PKScriptPubKey function in the code editor below.
The function should convert the input hex string to a Buffer.
Extract the public key (the first byte indicates the length: 0x41 for uncompressed, 0x21 for compressed).
Verify that the last byte is OP_CHECKSIG (0xAC).
Construct and return the ASM string: <public key in hex> OP_CHECKSIG

P2PK ScriptPubKey Decoder Exercise

// Simplified OPS object for this exercise
const OPS = {
  OP_CHECKSIG: 172,  // 0xac in decimal
};

const REVERSE_OPS = {
172: 'OP_CHECKSIG',
};

export function decodeP2PKScriptPubKey(hexScript) {
    // TODO: Implement the decodeP2PKScriptPubKey function
    // 1. Convert the hexScript to a Buffer
    // 2. Extract the length of the public key (first byte)
    // 3. Extract the public key
    // 4. Verify the last byte is OP_CHECKSIG
    // 5. Verify the script length
    // 6. Return the ASM format string
    // Your code here
}
;

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Start by converting the hexadecimal input to a Buffer using `Buffer.from(hexScript, 'hex')`. This allows you to work with the script as bytes.
Remember that the first byte of the script indicates the length of the public key. Use this to extract the public key from the Buffer.
The last byte of the script should always be OP_CHECKSIG (0xAC or 172 in decimal). Make sure to verify this.
To construct the ASM string, you'll need to convert the public key back to a hexadecimal string and append the OP_CHECKSIG operation. Use `toString('hex')` to convert the public key Buffer to a hex string.

Solution code

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Next: P2PKH - Pay To Public Key Hash