Examples from Script Verification

All examples from the script verification documentation chapter are shown here in full. The specific examples referenced in the subsections are wrapped in the functions listed below.

P2PKH Verification

• create_and_verify_p2pkh();

Libbitcoin API: Libbitcoin version 3. For version 4, script::verify() method has a simplified function signature. See code comments in the script below.

Compile with: g++ -std=c++11 -o script_verify script_verify_examples.cpp $(pkg-config --cflags libbitcoin --libs libbitcoin)

#include <bitcoin/bitcoin.hpp>
#include <string.h>
#include <iostream>

using namespace bc;
using namespace wallet;
using namespace chain;
using namespace machine;

// Testnet wallets.
auto my_secret0 = base16_literal(
    "b7423c94ab99d3295c1af7e7bbea47c75d298f7190ca2077b53bae61299b70a5");
ec_private my_private0(my_secret0, ec_private::testnet, true);
auto pubkey0 = my_private0.to_public().point();
auto my_address0 = my_private0.to_payment_address();

auto my_secret1 = base16_literal(
    "d977e2ce0f744dc3432cde9813a99360a3f79f7c8035ef82310d54c57332b2cc");
ec_private my_private1(my_secret1, ec_private::testnet, true);
auto pubkey1 = my_private1.to_public().point();


transaction create_example_transaction() {

  // Function creates single input tx template for all subsequent examples.
  //---------------------------------------------------------------------------

  // Destination output, a p2pkh script for example.
  std::string btc_amount = "0.998";
  uint64_t output_amount;
  decode_base10(output_amount, btc_amount, btc_decimal_places);
  auto p2pkh_script = script::to_pay_key_hash_pattern(
      bitcoin_short_hash(pubkey1));
  output p2pkh_output(output_amount, p2pkh_script);

  // Build example input.
  input example_input;
  std::string prev_tx =
      "44101b50393d01de1e113b17eb07e8a09fbf6334e2012575bc97da227958a7a5";
  hash_digest prev_tx_hash;
  decode_hash(prev_tx_hash,prev_tx);
  uint32_t index = 0;
  output_point uxto_to_spend(prev_tx_hash, index);
  example_input.set_previous_output(uxto_to_spend);
  example_input.set_sequence(max_input_sequence);

  // Build Transaction
  transaction tx;
  tx.set_version(1u);
  tx.inputs().push_back(example_input);
  tx.outputs().push_back(p2pkh_output);
  tx.set_locktime(0u);

  return tx;

}


void create_and_verify_p2pkh(const transaction& example_transaction)
{

  // Assumes relevant input script located at index 0.

  // Create local example_transaction copy.
  auto p2pkh_transaction = example_transaction;

  // Previous output script / Previous output amount.
  //---------------------------------------------------------------------------

  // Previous output script: P2PKH.
  auto p2pkh_output_script = script::to_pay_key_hash_pattern(
        bitcoin_short_hash(pubkey0));

  // Previous output amount.
  std::string previous_btc_amount = "1.0";
  uint64_t previous_output_amount;
  decode_base10(previous_output_amount, previous_btc_amount, btc_decimal_places);

  // Input script.
  //---------------------------------------------------------------------------

  // Signature.
  endorsement sig_0;
  uint8_t input0_index(0u);
  script::create_endorsement(sig_0, my_secret0, p2pkh_output_script,
      p2pkh_transaction, input0_index, sighash_algorithm::all);

  // Input script operations.
  operation::list input_operations {
      operation(sig_0),
      operation(to_chunk(pubkey0))
  };
  script p2pkh_input_script(input_operations);

  // Add input script to transaction.
  p2pkh_transaction.inputs()[input0_index].set_script(p2pkh_input_script);

  // Verify input script, output script.
  //---------------------------------------------------------------------------

  // With all fork rules.
  // Note: all rules includes testnet and regtest.
  witness empty_witness;
  auto ec = script::verify(p2pkh_transaction, input0_index,rule_fork::all_rules,
      p2pkh_input_script, empty_witness, p2pkh_output_script,
      previous_output_amount);

  // Libbitcoin  version4: Changes to script::verify().
  // Input script and witness parameters are moved into tx.
  // auto ec1 = script::verify(p2pkh_transaction, input0_index,
  //     rule_fork::all_rules, p2pkh_output_script, previous_output_amount);

  // Libbitcoin version4: Alternative script::verify() signature.
  // Prevout script and amount can be moved into tx metadata.
  // p2pkh_transaction.inputs()[input0_index]
  //     .previous_output().metadata.cache.set_script(p2pkh_output_script);
  // p2pkh_transaction.inputs()[input0_index]
  //     .previous_output().metadata.cache.set_value(previous_output_amount);
  // auto ec2 = script::verify(p2pkh_transaction, input0_index,
  //     rule_fork::all_rules);

  // Prints success
  std::cout << ec.message() << std::endl;

}

// TO DO: Other Examples

int main() {

  auto tx = create_example_transaction();

  create_and_verify_p2pkh(tx);

  return 0;

}