.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/consensus/pos/plot_04_casper_ffg.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_consensus_pos_plot_04_casper_ffg.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_consensus_pos_plot_04_casper_ffg.py:


Casper FFG: finality by two-thirds votes and slashing (Buterin and Griffith 2017)
=================================================================================

Casper the Friendly Finality Gadget overlays finality on a block chain.
Validators vote for links between checkpoints; a checkpoint is justified
when two thirds of the stake link to it from a justified checkpoint, and
finalized when its direct child is justified. Two slashing rules (no two
votes for one height; no vote surrounding another) guarantee that two
conflicting finalized checkpoints cost at least a third of all stake.
Ethereum's proof of stake uses it.

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

Checkpoints are finalized one behind the justified frontier. A validator
who equivocates or casts a surrounding vote is caught by comparing votes,
with no need to know which fork is correct.

The history behind this experiment: :doc:`/history/consensus_breakthroughs`.
See :doc:`/exercises/consensus` for a worked solution to the exercise.

.. GENERATED FROM PYTHON SOURCE LINES 25-27

Justify and finalize
--------------------

.. GENERATED FROM PYTHON SOURCE LINES 27-42

.. code-block:: Python

    import matplotlib.pyplot as plt

    import blockchainkit as bk

    stakes = {"v1": 25, "v2": 25, "v3": 25, "v4": 25}
    ffg = bk.consensus.FinalityGadget(stakes)
    history = []
    for height in range(1, 7):
        voters = ["v1", "v2", "v3"] if height != 4 else ["v1", "v2"]  # Height 4 misses quorum.
        for v in voters:
            ffg.vote(v, source=max(ffg.justified), target=height)
        history.append((height, max(ffg.justified), max(ffg.finalized)))
    print("justified:", sorted(ffg.justified), "finalized:", sorted(ffg.finalized))
    assert 4 not in ffg.justified and 3 not in ffg.finalized





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

 .. code-block:: none

    justified: [0, 1, 2, 3, 5, 6] finalized: [0, 1, 2, 5]




.. GENERATED FROM PYTHON SOURCE LINES 43-45

Slashable behaviour
-------------------

.. GENERATED FROM PYTHON SOURCE LINES 45-52

.. code-block:: Python

    ffg.vote("v4", source=0, target=7, checkpoint=b"fork A")
    ffg.vote("v4", source=0, target=7, checkpoint=b"fork B")  # Two votes for height 7.
    ffg.vote("v1", source=1, target=8)  # Surrounds v1's earlier vote (5 -> 6).
    offenses = {(o.validator, o.kind) for o in ffg.slashable}
    print(offenses)
    assert offenses == {("v4", "double vote"), ("v1", "surround vote")}





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

 .. code-block:: none

    {('v4', 'double vote'), ('v1', 'surround vote')}




.. GENERATED FROM PYTHON SOURCE LINES 53-65

.. code-block:: Python

    fig, ax = plt.subplots(figsize=(7, 3.5))
    heights, justified, finalized = zip(*history, strict=True)
    ax.step(heights, justified, where="post", label="latest justified")
    ax.step(heights, finalized, where="post", label="latest finalized")
    ax.set(
        xlabel="checkpoint voted for",
        ylabel="checkpoint height",
        title="Finality trails justification by one checkpoint",
    )
    ax.legend()
    fig.tight_layout()




.. image-sg:: /api/gallery/consensus/pos/images/sphx_glr_plot_04_casper_ffg_001.png
   :alt: Finality trails justification by one checkpoint
   :srcset: /api/gallery/consensus/pos/images/sphx_glr_plot_04_casper_ffg_001.png
   :class: sphx-glr-single-img





.. GENERATED FROM PYTHON SOURCE LINES 66-71

Exercise
--------
Two conflicting checkpoints are each finalized by two thirds of the stake.
Show that at least a third of the stake must have voted for both, and so
broke a slashing rule.


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

   **Total running time of the script:** (0 minutes 0.142 seconds)


.. _sphx_glr_download_api_gallery_consensus_pos_plot_04_casper_ffg.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/consensus/pos/plot_04_casper_ffg.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

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

      :download:`Download Jupyter notebook: plot_04_casper_ffg.ipynb <plot_04_casper_ffg.ipynb>`

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

      :download:`Download Python source code: plot_04_casper_ffg.py <plot_04_casper_ffg.py>`

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

      :download:`Download zipped: plot_04_casper_ffg.zip <plot_04_casper_ffg.zip>`


.. only:: html

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

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