.. DO NOT EDIT.
.. THIS FILE WAS AUTOMATICALLY GENERATED BY SPHINX-GALLERY.
.. TO MAKE CHANGES, EDIT THE SOURCE PYTHON FILE:
.. "api/gallery/fraud/phishing/plot_01_ice_phishing_approvals.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_fraud_phishing_plot_01_ice_phishing_approvals.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_fraud_phishing_plot_01_ice_phishing_approvals.py:


Approval ("ice") phishing on ERC-20 allowances (2022)
=====================================================

An ERC-20 ``approve`` lets a spender move the owner's tokens later without
asking again. Exchanges ask once for an unlimited allowance, so users learn
to sign approvals without reading them. In February 2022 Microsoft named
*ice phishing* the attack that exploits this: a fake airdrop or mint page
asks the victim to approve the attacker's contract, and the attacker
empties the wallet whenever it likes. Nothing is stolen from the keys; the
signature the victim reads in the wallet is the whole attack:

.. code-block:: solidity

   token.approve(0x9a1f...c3d7, type(uint256).max);   // "Claim your airdrop"

What a wallet stands to lose is the sum, over its tokens, of

.. math::

   \min\Big(\text{balance},\; \sum_{\text{spenders}} \text{allowance}\Big),

and revoking, approving 0, brings a spender's share back to nothing.

.. GENERATED FROM PYTHON SOURCE LINES 27-31

.. code-block:: Python

    import matplotlib.pyplot as plt

    import blockchainkit as bk








.. GENERATED FROM PYTHON SOURCE LINES 32-34

One signature on a fake airdrop page
------------------------------------

.. GENERATED FROM PYTHON SOURCE LINES 34-51

.. code-block:: Python


    world = bk.contracts.World()
    usdc = world.deploy("issuer", bk.contracts.ERC20, 10**6, name="USDC")
    dai = world.deploy("issuer", bk.contracts.ERC20, 10**6, name="DAI")
    world.transact("issuer", usdc, "transfer", "victim", 5_000)
    world.transact("issuer", dai, "transfer", "victim", 3_000)
    drainer = world.deploy("attacker", bk.fraud.Drainer, name="AirdropClaim")
    receipts = [
        world.transact("victim", usdc, "approve", "dex", bk.fraud.UNLIMITED),  # A real exchange.
        world.transact("victim", usdc, "approve", drainer, bk.fraud.UNLIMITED),  # The phish.
        world.transact("victim", dai, "approve", drainer, 1_000),
    ]
    approvals = bk.fraud.open_approvals(receipts, "victim")
    exposed = bk.fraud.allowance_exposure(world, "victim", approvals)
    print("standing approvals:", len(approvals), "| at risk:", exposed)
    assert exposed == 6_000





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

 .. code-block:: none

    standing approvals: 3 | at risk: 6000




.. GENERATED FROM PYTHON SOURCE LINES 52-54

Months later: one revoked, one forgotten
----------------------------------------

.. GENERATED FROM PYTHON SOURCE LINES 54-73

.. code-block:: Python


    world.advance(blocks=200_000)
    receipts.append(world.transact("victim", dai, "approve", drainer, 0))
    remaining = bk.fraud.open_approvals(receipts, "victim")
    print("after revoking DAI:", bk.fraud.allowance_exposure(world, "victim", remaining), "at risk")
    swept = [world.transact("attacker", drainer, "sweep", t, "victim").result for t in (usdc, dai)]
    print("swept USDC, DAI:", swept)
    assert swept == [5_000, 0]

    fig, ax = plt.subplots(figsize=(7, 3.5))
    labels = ["USDC (approved, forgotten)", "DAI (approved, revoked)"]
    ax.barh(labels, [5_000, 3_000], color="#cbd5e1", label="held")
    ax.barh(labels, swept, color="#dc2626", label="taken by the drainer")
    ax.set(xlabel="tokens", title="An allowance outlives the page that asked for it")
    ax.legend()
    fig.tight_layout()

    plt.show()




.. image-sg:: /api/gallery/fraud/phishing/images/sphx_glr_plot_01_ice_phishing_approvals_001.png
   :alt: An allowance outlives the page that asked for it
   :srcset: /api/gallery/fraud/phishing/images/sphx_glr_plot_01_ice_phishing_approvals_001.png
   :class: sphx-glr-single-img


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

 .. code-block:: none

    after revoking DAI: 5000 at risk
    swept USDC, DAI: [5000, 0]




.. GENERATED FROM PYTHON SOURCE LINES 74-79

Exercise
--------
EIP-2612 replaces the ``approve`` transaction with a signed ``permit``
message that anyone can submit. Why does this make ice phishing easier to
carry out and harder to notice?


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

   **Total running time of the script:** (0 minutes 0.029 seconds)


.. _sphx_glr_download_api_gallery_fraud_phishing_plot_01_ice_phishing_approvals.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/fraud/phishing/plot_01_ice_phishing_approvals.ipynb
        :alt: Launch JupyterLite
        :width: 150 px

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

      :download:`Download Jupyter notebook: plot_01_ice_phishing_approvals.ipynb <plot_01_ice_phishing_approvals.ipynb>`

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

      :download:`Download Python source code: plot_01_ice_phishing_approvals.py <plot_01_ice_phishing_approvals.py>`

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

      :download:`Download zipped: plot_01_ice_phishing_approvals.zip <plot_01_ice_phishing_approvals.zip>`


.. only:: html

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

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