test_unrecoverable_signature()

Documentation for tests/frontier/validation/test_transaction.py::test_unrecoverable_signature@814481c0.

Generate fixtures for these test cases for Amsterdam with:

fill -v tests/frontier/validation/test_transaction.py::test_unrecoverable_signature --fork Amsterdam

A signature whose components are each individually in range but which recovers no public key must be rejected.

test_bad_v_r_s covers the RANGE rules (v below 27/35, r or s at or above secp256k1n, s above the EIP-2 halfway point). This is the distinct failure that lies inside those ranges: r is read as the x-coordinate of the ephemeral point R, and only about half of the values in [1, n) are x-coordinates of a curve point at all. For the other half there is no R, hence no public key and no sender -- with no range check violated anywhere.

A client that guards recovery by range-checking alone, or that treats the two failures as different kinds of error, reaches this case through an unintended path.

Source code in tests/frontier/validation/test_transaction.py

@pytest.mark.inclusion_test
@pytest.mark.valid_from("Frontier")
@pytest.mark.exception_test
@pytest.mark.eels_base_coverage
@pytest.mark.parametrize(
    "tx_type",
    [
        pytest.param(0, id="legacy"),
        pytest.param(1, id="eip2930", marks=pytest.mark.valid_from("Berlin")),
        pytest.param(2, id="eip1559", marks=pytest.mark.valid_from("London")),
    ],
)
def test_unrecoverable_signature(
    state_test: StateTestFiller,
    pre: Alloc,
    tx_type: int,
) -> None:
    """
    A signature whose components are each individually in range but which
    recovers no public key must be rejected.

    `test_bad_v_r_s` covers the RANGE rules (`v` below 27/35, `r` or `s` at or
    above secp256k1n, `s` above the EIP-2 halfway point). This is the distinct
    failure that lies inside those ranges: `r` is read as the x-coordinate of
    the ephemeral point R, and only about half of the values in [1, n) are
    x-coordinates of a curve point at all. For the other half there is no R,
    hence no public key and no sender -- with no range check violated anywhere.

    A client that guards recovery by range-checking alone, or that treats the
    two failures as different kinds of error, reaches this case through an
    unintended path.
    """
    to = pre.fund_eoa(0xDEADBEEE)

    tx = Transaction(
        sender=pre.fund_eoa(),
        to=to,
        error=TransactionException.INVALID_SIGNATURE_VRS,
        ty=tx_type,
        value=1,
        # Legacy encodes the (unprotected) recovery id in v; typed
        # transactions carry the parity bit directly.
        v=27 if tx_type == 0 else 0,
        r=UNRECOVERABLE_R,
        s=1,
    )

    state_test(
        pre=pre,
        # Transaction rejected: the recipient keeps exactly its funded balance.
        post={to: Account(balance=0xDEADBEEE)},
        tx=tx,
    )

Parametrized Test Cases

This test generates 3 parametrized test cases across 16 forks.