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"""
This module provides functionality inspired by the Refined-Power Analysis attack by Goubin:
A Refined Power-Analysis Attack on Elliptic Curve Cryptosystems, Louis Goubin, PKC '03
`<https://dl.acm.org/doi/10.5555/648120.747060>`_
"""
from public import public
from typing import MutableMapping, Optional
from ...ec.formula import (
FormulaAction,
DoublingFormula,
AdditionFormula,
TriplingFormula,
NegationFormula,
DifferentialAdditionFormula,
LadderFormula,
)
from ...ec.mult import ScalarMultiplicationAction, PrecomputationAction
from ...ec.point import Point
from ...ec.context import Context, Action
@public
class MultipleContext(Context):
"""A context that traces the multiples of points computed."""
base: Optional[Point]
points: MutableMapping[Point, int]
inside: bool
def __init__(self):
self.base = None
self.points = {}
self.inside = False
def enter_action(self, action: Action) -> None:
if isinstance(action, (ScalarMultiplicationAction, PrecomputationAction)):
self.base = action.point
self.points = {self.base: 1}
self.inside = True
def exit_action(self, action: Action) -> None:
if isinstance(action, (ScalarMultiplicationAction, PrecomputationAction)):
self.inside = False
if isinstance(action, FormulaAction) and self.inside:
if isinstance(action.formula, DoublingFormula):
inp = action.input_points[0]
out = action.output_points[0]
self.points[out] = 2 * self.points[inp]
elif isinstance(action.formula, TriplingFormula):
inp = action.input_points[0]
out = action.output_points[0]
self.points[out] = 3 * self.points[inp]
elif isinstance(action.formula, AdditionFormula):
one, other = action.input_points
out = action.output_points[0]
self.points[out] = self.points[one] + self.points[other]
elif isinstance(action.formula, NegationFormula):
inp = action.input_points[0]
out = action.output_points[0]
self.points[out] = -self.points[inp]
elif isinstance(action.formula, DifferentialAdditionFormula):
diff, one, other = action.input_points
out = action.output_points[0]
self.points[out] = self.points[one] + self.points[other]
elif isinstance(action.formula, LadderFormula):
diff, one, other = action.input_points
dbl, add = action.output_points
self.points[add] = self.points[one] + self.points[other]
self.points[dbl] = 2 * self.points[one]
def __repr__(self):
return f"{self.__class__.__name__}({self.base!r}, multiples={self.points.values()!r})"
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