Fix ladder multipliers.

4 files changed, 47 insertions, 7 deletions

diff --git a/pyecsca/ec/curve.py b/pyecsca/ec/curve.py
index 4c9d401..20dd3e0 100644
--- a/pyecsca/ec/curve.py
+++ b/pyecsca/ec/curve.py
@@ -1,3 +1,4 @@
+from public import public
 from typing import Mapping
 
 from .coordinates import CoordinateModel
@@ -5,6 +6,7 @@ from .model import CurveModel
 from .point import Point
 
 
+@public
 class EllipticCurve(object):
     model: CurveModel
     coordinate_model: CoordinateModel
diff --git a/pyecsca/ec/formula.py b/pyecsca/ec/formula.py
index 5b6f028..e155282 100644
--- a/pyecsca/ec/formula.py
+++ b/pyecsca/ec/formula.py
@@ -1,5 +1,6 @@
 from ast import parse, Expression, Module
 from pkg_resources import resource_stream
+from public import public
 from typing import List, Any
 
 
@@ -53,36 +54,43 @@ class Formula(object):
         return f"{self.__class__.__name__}({self.name} for {self.coordinate_model})"
 
 
+@public
 class AdditionFormula(Formula):
     _inputs = 2
     _outputs = 1
 
 
+@public
 class DoublingFormula(Formula):
     _inputs = 1
     _outputs = 1
 
 
+@public
 class TriplingFormula(Formula):
     _inputs = 1
     _outputs = 1
 
 
+@public
 class NegationFormula(Formula):
     _inputs = 1
     _outputs = 1
 
 
+@public
 class ScalingFormula(Formula):
     _inputs = 1
     _outputs = 1
 
 
+@public
 class DifferentialAdditionFormula(Formula):
     _inputs = 3
     _outputs = 1
 
 
+@public
 class LadderFormula(Formula):
     _inputs = 3
     _outputs = 2
diff --git a/pyecsca/ec/mod.py b/pyecsca/ec/mod.py
index bc1ebff..c8c9a92 100644
--- a/pyecsca/ec/mod.py
+++ b/pyecsca/ec/mod.py
@@ -1,6 +1,7 @@
 from functools import wraps
+from public import public
 
-
+@public
 def gcd(a, b):
     if abs(a) < abs(b):
         return gcd(b, a)
@@ -11,7 +12,7 @@ def gcd(a, b):
 
     return a
 
-
+@public
 def extgcd(a, b):
     if abs(b) > abs(a):
         (x, y, d) = extgcd(b, a)
@@ -42,7 +43,7 @@ def check(func):
 
     return method
 
-
+@public
 class Mod(object):
 
     def __init__(self, x: int, n: int):
diff --git a/pyecsca/ec/mult.py b/pyecsca/ec/mult.py
index c0fe994..d7c5bc6 100644
--- a/pyecsca/ec/mult.py
+++ b/pyecsca/ec/mult.py
@@ -1,4 +1,5 @@
 from copy import copy
+from public import public
 from typing import Mapping, Tuple, Optional, MutableMapping
 
 from pyecsca.ec.naf import naf, wnaf
@@ -74,6 +75,7 @@ class ScalarMultiplier(object):
         raise NotImplementedError
 
 
+@public
 class LTRMultiplier(ScalarMultiplier):
     always: bool
 
@@ -97,6 +99,7 @@ class LTRMultiplier(ScalarMultiplier):
         return r
 
 
+@public
 class RTLMultiplier(ScalarMultiplier):
     always: bool
 
@@ -121,6 +124,7 @@ class RTLMultiplier(ScalarMultiplier):
         return r
 
 
+@public
 class LadderMultiplier(ScalarMultiplier):
 
     def __init__(self, curve: EllipticCurve, ladd: LadderFormula, scl: ScalingFormula = None,
@@ -131,16 +135,40 @@ class LadderMultiplier(ScalarMultiplier):
         q = self._init_multiply(point)
         p0 = copy(q)
         p1 = self._ladd(self.curve.neutral, q, q)[1]
-        for i in range(scalar.bit_length(), -1, -1):
-            if scalar & i != 0:
-                p0, p1 = self._ladd(q, p1, p0)
-            else:
+        for i in range(scalar.bit_length() - 1, -1, -1):
+            if scalar & (1 << i) != 0:
                 p0, p1 = self._ladd(q, p0, p1)
+            else:
+                p1, p0 = self._ladd(q, p1, p0)
+        if "scl" in self.formulas:
+            p0 = self._scl(p0)
+        return p0
+
+
+@public
+class SimpleLadderMultiplier(ScalarMultiplier):
+
+    def __init__(self, curve: EllipticCurve, add: AdditionFormula, dbl: DoublingFormula,
+                 scl: ScalingFormula = None, ctx: Context = None):
+        super().__init__(curve, ctx, add=add, dbl=dbl, scl=scl)
+
+    def multiply(self, scalar: int, point: Optional[Point] = None) -> Point:
+        q = self._init_multiply(point)
+        p0 = copy(q)
+        p1 = self._dbl(q)
+        for i in range(scalar.bit_length() - 2, -1, -1):
+            if scalar & (1 << i) != 0:
+                p0 = self._add(p0, p1)
+                p1 = self._dbl(p1)
+            else:
+                p1 = self._add(p0, p1)
+                p0 = self._dbl(p0)
         if "scl" in self.formulas:
             p0 = self._scl(p0)
         return p0
 
 
+@public
 class BinaryNAFMultiplier(ScalarMultiplier):
     _point_neg: Point
 
@@ -167,6 +195,7 @@ class BinaryNAFMultiplier(ScalarMultiplier):
         return q
 
 
+@public
 class WindowNAFMultiplier(ScalarMultiplier):
     _points: MutableMapping[int, Point]
     _width: int