Exercise 1: Medium

In this exercise, you'll construct a P2SH (Pay-to-Script-Hash) ScriptPubKey for a given redeem script within a partially constructed transaction.

Here's a breakdown of the partially constructed transaction:

FieldValue
Version02000000
Input Count02
Input 1 TXID

589d75a45b732e3a92da560086568310e33efe5cfb26bcb2685d7ee712af7a3e

Input 1 VOUT00000000
Input 1 ScriptSig Size6a
Input 1 ScriptSig[scriptsig 1]
Input 1 Sequencefdffffff
Input 2 TXID

2f8ec63af69ea6d35acb217562bef0467b0354a2dad430a71051041e5cfd0499

Input 2 VOUT01000000
Input 2 ScriptSig Size6b
Input 2 ScriptSig[scriptsig 2]
Input 2 Sequencefdffffff
Output Count02
Output 1 Amount

888a0100000000000

Output 1 ScriptPubKey Size17
Output 1 ScriptPubKey[scriptpubkey]
Output 2 Amount74658b0000000000
Output 2 ScriptPubKey

1976a91468cfed146aced22f422a68015ff8ca180761912a88ac

Locktimeeff91700

The hexadecimal representation of this transaction is:

text
10200000002589d75a45b732e3a92da560086568310e33efe5cfb26bcb2685d7ee712af7a3e000000006a-[scriptsig 1]-fdffffff2f8ec63af69ea6d35acb217562bef0467b0354a2dad430a71051041e5cfd0499010000006b-[scriptsig 2]-fdffffff02888a01000000000017-[scriptpubkey]-74658b00000000001976a91468cfed146aced22f422a68015ff8ca180761912a88aceff91700

Exercise

Your task is to complete the constructP2SHScriptPubKey function which creates a P2SH ScriptPubKey for the following redeem script:

text
    2 3 ADD 5 EQUAL

Instructions:

  1. Implement the constructP2SHScriptPubKey function.
  2. The function should take the redeem script as input and return the complete P2SH ScriptPubKey.
  3. Remember to hash the redeem script and include the necessary opcodes.
  4. The provided unit test will check if your implementation is correct.

Choose your preferred language below to start coding:

P2PK ScriptPubKey Decoder Exercise
import CryptoJS from 'crypto-js';

export function constructP2SHScriptPubKey(redeemScript) {
  // TODO: Implement this function
  // Hint: Use CryptoJS.SHA256 and CryptoJS.RIPEMD160 for hashing
}
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Ready to Code?

Choose your preferred language to begin

For this exercise, we've provided the crypto-js library to help with the hashing operations. You should use this library to implement the P2SH ScriptPubKey function.

You can look up the hex characters for each op_code in the Bitcoin Script wiki page.

Click to reveal next hint (0/5)
  • Start by encoding the redeem script as bytes.
  • Use CryptoJS.SHA256 to hash the redeem script, then use CryptoJS.RIPEMD160 on the result.
  • The P2SH script starts with OP_HASH160 (0xa9).
  • Push the 20-byte script hash onto the stack (0x14 followed by the hash).
  • End the script with OP_EQUAL (0x87).

Solution code

Inspiration

After completing the exercise, you can check out these testnet transactions to see real P2SH ScriptPubKeys in action:

These transactions demonstrate how P2SH ScriptPubKeys are used in actual Bitcoin transactions on the testnet.

Next
Exercise 2: Hard