.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/vm/script/plot_01_p2pkh.py"
.. LINE NUMBERS ARE GIVEN BELOW.

.. only:: html

    .. note::
        :class: sphx-glr-download-link-note

        :ref:`Go to the end <sphx_glr_download_api_gallery_vm_script_plot_01_p2pkh.py>`
        to download the full example code or to run this example in your browser via JupyterLite.

.. rst-class:: sphx-glr-example-title

.. _sphx_glr_api_gallery_vm_script_plot_01_p2pkh.py:


Bitcoin Script: pay to public-key hash (Nakamoto 2009)
======================================================

Bitcoin does not record owners. Each coin carries a *locking script*, and
spending it means supplying an *unlocking script* that makes the pair
succeed. The standard lock, pay-to-public-key-hash, says: "show a public key
with this hash, and a signature by it over the spending transaction". Script
is a Forth-like stack language with no loops, so a script of n operations
runs at most n steps: Bitcoin needs no gas.

What to look for
----------------

The owner's spend passes; a different key fails at ``OP_EQUALVERIFY``, and the
right key with a signature over a different transaction fails at
``OP_CHECKSIG``. The operation count never exceeds the script length.

The history behind this experiment: :doc:`/history/vm_breakthroughs`.

.. GENERATED FROM PYTHON SOURCE LINES 23-25

Lock a coin to Alice's key hash
-------------------------------

.. GENERATED FROM PYTHON SOURCE LINES 25-60

.. code-block:: Python

    import matplotlib.pyplot as plt

    import blockchainkit as bk
    from blockchainkit.crypto import public_key, sign

    alice = public_key(7)
    lock = bk.vm.p2pkh_locking(alice)
    print([item if isinstance(item, str) else item.hex()[:16] + "..." for item in lock])
    spend = b"spend coin 0: 5 to carol"
    attempts = {
        "Alice signs": (bk.vm.p2pkh_unlocking(sign(spend, 7, nonce=11), alice), spend),
        "Mallory's key": (bk.vm.p2pkh_unlocking(sign(spend, 9, nonce=11), public_key(9)), spend),
        "replayed signature": (
            bk.vm.p2pkh_unlocking(sign(spend, 7, nonce=11), alice),
            b"spend coin 0: 5 to mallory",
        ),
    }
    results = {
        name: bk.vm.verify_script(unlock, lock, message=message)
        for name, (unlock, message) in attempts.items()
    }
    for name, result in results.items():
        print(f"{name:18s} valid={result.valid}  {result.error or ''}")
    assert [r.valid for r in results.values()] == [True, False, False]
    assert all(r.operations <= len(lock) + 2 for r in results.values())

    fig, ax = plt.subplots(figsize=(7, 3))
    ax.barh(
        list(results), [r.operations for r in results.values()], color=["#16a34a", "#dc2626", "#dc2626"]
    )
    ax.axvline(len(lock) + 2, color="black", linestyle="--", label="script length")
    ax.set(xlabel="operations executed", title="Scripts cannot loop")
    ax.legend()
    fig.tight_layout()




.. image-sg:: /api/gallery/vm/script/images/sphx_glr_plot_01_p2pkh_001.png
   :alt: Scripts cannot loop
   :srcset: /api/gallery/vm/script/images/sphx_glr_plot_01_p2pkh_001.png
   :class: sphx-glr-single-img


.. rst-class:: sphx-glr-script-out

 .. code-block:: none

    ['OP_DUP', 'OP_HASH256', 'cfbf53e6b14b8df9...', 'OP_EQUALVERIFY', 'OP_CHECKSIG']
    Alice signs        valid=True  
    Mallory's key      valid=False  OP_EQUALVERIFY: items differ
    replayed signature valid=False  the top of the stack is not true




.. GENERATED FROM PYTHON SOURCE LINES 61-66

Exercise
--------
Write a 2-of-2 lock that requires signatures from both Alice and Bob
using only the opcodes available (hint: ``OP_CHECKSIG`` then
``OP_VERIFY``). Why did Bitcoin later add ``OP_CHECKMULTISIG``?


.. rst-class:: sphx-glr-timing

   **Total running time of the script:** (0 minutes 0.132 seconds)


.. _sphx_glr_download_api_gallery_vm_script_plot_01_p2pkh.py:

.. only:: html

  .. container:: sphx-glr-footer sphx-glr-footer-example

    .. container:: lite-badge

      .. image:: images/jupyterlite_badge_logo.svg
        :target: ../../../../lite/lab/index.html?path=api/gallery/vm/script/plot_01_p2pkh.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

    .. container:: sphx-glr-download sphx-glr-download-jupyter

      :download:`Download Jupyter notebook: plot_01_p2pkh.ipynb <plot_01_p2pkh.ipynb>`

    .. container:: sphx-glr-download sphx-glr-download-python

      :download:`Download Python source code: plot_01_p2pkh.py <plot_01_p2pkh.py>`

    .. container:: sphx-glr-download sphx-glr-download-zip

      :download:`Download zipped: plot_01_p2pkh.zip <plot_01_p2pkh.zip>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.github.io>`_