diff --git a/src/models.py b/src/models.py
index 7192274..6c9b9de 100644
--- a/src/models.py
+++ b/src/models.py
@@ -116,6 +116,14 @@ class OuterKey(DarcKey):
             matrix=matrix,
         )
 
+    @classmethod
+    def init_identity_matrix(cls, height: int):
+        """ originally buildRandom """
+        matrix = [list(range(height))]
+        return OuterKey(
+            matrix=matrix,
+        )
+
 
 class InnerKey(DarcKey):
     key_type: DarcKeyType = DarcKeyType.inner_shuffle
@@ -128,6 +136,14 @@ class InnerKey(DarcKey):
             matrix=matrix,
         )
 
+    @classmethod
+    def init_identity_matrix(cls, width: int, height: int):
+        """ originally buildRandom """
+        matrix = [list(range(width)) for _ in range(height)]
+        return InnerKey(
+            matrix=matrix,
+        )
+
 
 class SubstitutionKey(DarcKey):
     key_type: DarcKeyType = DarcKeyType.substitution
@@ -138,7 +154,14 @@ class SubstitutionKey(DarcKey):
         matrix = [cls._random_mask(width, max_value) for _ in range(height)]
         return SubstitutionKey(
             matrix=matrix,
-            max_value=max_value
+        )
+
+    @classmethod
+    def init_identity_matrix(cls, width: int, height: int):
+        """ originally buildScramble """
+        matrix = [[0 for _ in range(width)] for _ in range(height)]
+        return SubstitutionKey(
+            matrix=matrix,
         )
 
 
diff --git a/test/test_darc.py b/test/test_darc.py
index a283fc7..420e0f2 100644
--- a/test/test_darc.py
+++ b/test/test_darc.py
@@ -12,7 +12,7 @@ import pytest
 )
 def test_darc(height, width, message_len):
     alphabet = SubstitutionKey.init_matrix(width, height, 255)
-    medium = SubstitutionKey(matrix=[[0 for _ in range(width)] for _ in range(height)])
+    medium = SubstitutionKey.init_identity_matrix(width, height)
 
     server_keys, mutual_keys, client_keys = generate_keys(height, width)
     original_message = OuterKey.init_matrix(height).matrix[0]