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"""
Provides functionality inspired by the Exceptional Procedure Attack [EPA]_.
"""
from typing import Callable, Literal, Type, Union
from public import public
from pyecsca.ec.context import local
from pyecsca.ec.formula.fake import FakePoint
from pyecsca.ec.mult import ScalarMultiplier
from pyecsca.ec.mult.fake import cached_fake_mult
from pyecsca.ec.params import DomainParameters
from pyecsca.sca.re.rpa import MultipleContext
@public
def errors_out(
scalar: int,
params: DomainParameters,
mult_class: Type[ScalarMultiplier],
mult_factory: Callable,
check_funcs: dict[str, Callable],
check_condition: Union[Literal["all"], Literal["necessary"]],
precomp_to_affine: bool,
) -> bool:
"""
:param scalar:
:param params:
:param mult_class:
:param mult_factory:
:param check_funcs:
:param check_condition:
:param precomp_to_affine:
:return:
.. note::
The scalar multiplier must not short-circuit.
"""
mult = cached_fake_mult(mult_class, mult_factory, params)
ctx = MultipleContext(keep_base=True)
with local(ctx, copy=False):
mult.init(params, FakePoint(params.curve.coordinate_model))
with local(ctx, copy=False):
out = mult.multiply(scalar)
affine_points = {out, *ctx.precomp.values()} if precomp_to_affine else {out}
if check_condition == "all":
points = set(ctx.points.keys())
elif check_condition == "necessary":
points = set(affine_points)
queue = set(affine_points)
while queue:
point = queue.pop()
for parent in ctx.parents[point]:
points.add(parent)
queue.add(parent)
else:
raise ValueError("check_condition must be 'all' or 'necessary'")
# Special case the "to affine" transform and checks
# This actually passes the multiple itself to the check, not the inputs(parents)
for point in affine_points:
if "affine" in check_funcs:
func = check_funcs["affine"]
if func(ctx.points[point]):
return True
# Now handle the regular checks
for point in points:
formula = ctx.formulas[point]
if formula in check_funcs:
func = check_funcs[formula]
inputs = list(map(lambda pt: ctx.points[pt], ctx.parents[point]))
if func(*inputs):
return True
return False
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