.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/wallets/addresses/plot_03_bech32m_checksum_flaw.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_wallets_addresses_plot_03_bech32m_checksum_flaw.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_wallets_addresses_plot_03_bech32m_checksum_flaw.py:


Bech32m and the insertion flaw in Bech32 (BIP350, 2020)
=======================================================

In 2019 it was found that Bech32 has a blind spot: when a string ends in
``p``, inserting or deleting ``q`` characters just before that ``p`` leaves
the checksum valid. ``q`` is the value 0, and ``p`` is 1, the constant the
checksum must leave, so the extra zeros multiply the polynomial by powers
of x without changing its remainder. Witness version 0 survives, because
its programs must be 20 or 32 bytes, but Taproot's version 1 and later
allow other lengths. Pieter Wuille's Bech32m changes only the constant,

.. math::

   \mathrm{polymod}(\dots) = \texttt{0x2bc830a3},

and is required from witness version 1 on.

.. GENERATED FROM PYTHON SOURCE LINES 21-25

.. code-block:: Python

    import matplotlib.pyplot as plt

    import blockchainkit as bk








.. GENERATED FROM PYTHON SOURCE LINES 26-28

A string ending in p
--------------------

.. GENERATED FROM PYTHON SOURCE LINES 28-56

.. code-block:: Python



    def ending_in_p(encoding):
        for n in range(1_000):
            data = [n % 32, n // 32 % 32, 7, 3, 1]
            text = bk.wallets.bech32_encode("bc", data, encoding)
            if text.endswith("p"):
                return text
        raise ValueError("no string found")


    def accepts(text):
        try:
            bk.wallets.bech32_decode(text)
        except ValueError:
            return False
        return True


    original = ending_in_p("bech32")
    print("original:", original)
    inserted = {}
    for encoding in ("bech32", "bech32m"):
        text = ending_in_p(encoding)
        inserted[encoding] = [accepts(text[:-1] + "q" * k + "p") for k in range(1, 9)]
        print(f"{encoding:8} with 1..8 q's inserted:", inserted[encoding])
    assert all(inserted["bech32"]) and not any(inserted["bech32m"])





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

 .. code-block:: none

    original: bc1sq8rpprd0lp
    bech32   with 1..8 q's inserted: [True, True, True, True, True, True, True, True]
    bech32m  with 1..8 q's inserted: [False, False, False, False, False, False, False, False]




.. GENERATED FROM PYTHON SOURCE LINES 57-59

Why version 0 was safe
----------------------

.. GENERATED FROM PYTHON SOURCE LINES 59-82

.. code-block:: Python


    program = bytes(20)
    v0 = bk.wallets.segwit_encode("bc", 0, program)
    assert bk.wallets.segwit_decode("bc", v0).program == program
    taproot = bk.wallets.segwit_encode("bc", 1, bytes(32))
    print("version 0:", v0)
    print("version 1:", taproot, bk.wallets.bech32_decode(taproot).encoding)

    fig, ax = plt.subplots(figsize=(6, 4))
    k = list(range(1, 9))
    ax.plot(k, inserted["bech32"], "o-", color="#dc2626", label="Bech32")
    ax.plot(k, inserted["bech32m"], "o-", color="#2563eb", label="Bech32m")
    ax.set(
        xlabel="q characters inserted before the final p",
        ylabel="accepted",
        yticks=[0, 1],
        yticklabels=["no", "yes"],
    )
    ax.set_title("A new constant closes the insertion hole")
    ax.legend()
    fig.tight_layout()
    plt.show()




.. image-sg:: /api/gallery/wallets/addresses/images/sphx_glr_plot_03_bech32m_checksum_flaw_001.png
   :alt: A new constant closes the insertion hole
   :srcset: /api/gallery/wallets/addresses/images/sphx_glr_plot_03_bech32m_checksum_flaw_001.png
   :class: sphx-glr-single-img


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

 .. code-block:: none

    version 0: bc1qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq9e75rs
    version 1: bc1pqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqpqqenm bech32m




.. GENERATED FROM PYTHON SOURCE LINES 83-88

Exercise
--------
Does deleting a ``q`` before a final ``p`` fool Bech32 too? Find a string
ending in ``qp`` and try.
A worked solution is in :doc:`/exercises/wallets`.


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

   **Total running time of the script:** (0 minutes 0.049 seconds)


.. _sphx_glr_download_api_gallery_wallets_addresses_plot_03_bech32m_checksum_flaw.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/wallets/addresses/plot_03_bech32m_checksum_flaw.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

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

      :download:`Download Jupyter notebook: plot_03_bech32m_checksum_flaw.ipynb <plot_03_bech32m_checksum_flaw.ipynb>`

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

      :download:`Download Python source code: plot_03_bech32m_checksum_flaw.py <plot_03_bech32m_checksum_flaw.py>`

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

      :download:`Download zipped: plot_03_bech32m_checksum_flaw.zip <plot_03_bech32m_checksum_flaw.zip>`


.. only:: html

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

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