cleanup to read as equation

src/models.py

@@ -106,23 +106,6 @@ class DarcKey(BaseModel):
 
         return True
 
-    def column_substitution(self, column: int, substitution: list[int]):
-        assert len(substitution) == len(self.matrix)
-        assert len(self.matrix[0]) > column >= 0
-        output = []
-        for i, el in enumerate(self.matrix):
-            row = []
-            for j, el2 in enumerate(el):
-                if j == column:
-                    row.append(substitution[i])
-                else:
-                    row.append(el2)
-            output.append(row)
-        return DarcKey(
-            matrix=output,
-            key_type=self.key_type
-        )
-
 
 class OuterKey(DarcKey):
     key_type = DarcKeyTypes.outer_shuffle
@@ -162,6 +145,25 @@ class AlphabetKey(DarcKey):
         )
 
 
+class Mask(DarcKey):
+    key_type = DarcKeyTypes.alphabet
+    max_value: int = 255
+
+    @classmethod
+    def init_matrix(cls, width: int, height: int, col_mask: int):
+        """ originally buildScramble """
+
+        mask = cls._random_mask(width, cls.max_value)
+        matrix = [[0 for _ in range(width)] for _ in range(height)]
+        if col_mask < height:
+            matrix[col_mask] = mask
+
+        return Mask(
+            matrix=matrix,
+            max_value=cls.max_value
+        )
+
+
 class ClientEphemeralDataKeys(BaseModel):
     outer_key_1: OuterKey
     outer_key_2: OuterKey