From 46634275e4d277c3f78c783b263971ef3f6108d6 Mon Sep 17 00:00:00 2001
From: David Huh <38101884+qt1337@users.noreply.github.com>
Date: Mon, 18 Oct 2021 14:57:22 +0200
Subject: [PATCH] :sparkles: Added Lineares Schieberegister

- no comments
---
 chapter_one/Verschiebe-Chiffre.py         |  2 --
 chapter_three/Lineares-Schieberegister.py | 41 +++++++++++++++++++++++
 utils/CipherUtils.py                      |  9 +++++
 3 files changed, 50 insertions(+), 2 deletions(-)
 create mode 100644 chapter_three/Lineares-Schieberegister.py

diff --git a/chapter_one/Verschiebe-Chiffre.py b/chapter_one/Verschiebe-Chiffre.py
index b419bd4..9c85324 100644
--- a/chapter_one/Verschiebe-Chiffre.py
+++ b/chapter_one/Verschiebe-Chiffre.py
@@ -38,8 +38,6 @@ def shift_text(cleartext: str, incrementation: int):
     return shifted_text
 
 
-
-
 def brute_force_example(cleartext: str = 'Bitcoin', incrementation: int = 7):
     """
     This is an example of how to bruteforce an encrypted text. (Encrypted with Letter-Shifting)
diff --git a/chapter_three/Lineares-Schieberegister.py b/chapter_three/Lineares-Schieberegister.py
new file mode 100644
index 0000000..6acb1f2
--- /dev/null
+++ b/chapter_three/Lineares-Schieberegister.py
@@ -0,0 +1,41 @@
+from utils import CipherUtils
+
+CLEAR_LIST = [0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 0, 0, 1]
+INIT_STATE = [0, 1, 1, 0]
+COEFFICIENTS = [1, 1, 1, 0]
+
+
+def create_shift_register(init_state: list, coefficients: list):
+    return_list = []
+    current_state = init_state.copy()
+    current_state_list = [current_state.copy()]
+
+    if (size := len(init_state)) != len(coefficients):
+        print('Length of lists does not match.')
+        exit()
+
+    for x in range(2 ** size):
+        return_list.append(current_state[-1])
+        new_state_value = 0
+        for i in range(size):
+            new_state_value = (new_state_value + current_state[i] ^ coefficients[i]) % 2
+
+        current_state.insert(0, new_state_value)
+        current_state.pop(-1)
+
+        if current_state in current_state_list:
+            return_list.extend(current_state[1:][::-1])
+            break
+        current_state_list.append(current_state.copy())
+
+    return return_list
+
+
+if __name__ == '__main__':
+    key = create_shift_register(INIT_STATE, COEFFICIENTS)
+
+    encrypted = CipherUtils.xor_two_lists(CLEAR_LIST, key)
+    decrypted = CipherUtils.xor_two_lists(encrypted, key)
+    print(CLEAR_LIST)
+    print(encrypted)
+    print(decrypted)
diff --git a/utils/CipherUtils.py b/utils/CipherUtils.py
index 4d90451..2671530 100644
--- a/utils/CipherUtils.py
+++ b/utils/CipherUtils.py
@@ -93,6 +93,15 @@ def shift_char(char, incrementation: int = 1):
     return str(new_char_in_bytes)[2]
 
 
+def xor_two_lists(clear_list, key_list):
+    xored_list = []
+
+    for x in range(len(clear_list)):
+        xored_list.append(clear_list[x] ^ key_list[x % len(key_list)])
+
+    return xored_list
+
+
 if __name__ == '__main__':
     print(
         calculate_frequency('Hier den Text eingeben, für den die Wahrscheinlichkeiten berechnet werden sollen', True))