From 75d157bfef1499e5a3c42878ee1a70ba3213bd92 Mon Sep 17 00:00:00 2001
From: MegCooper <megrcooper1166@@outlook.com>
Date: Wed, 30 Aug 2023 15:46:24 +0100
Subject: [PATCH] Added Hill Cypher

Added a simple Hill cypher that uses a 3x3 Matrix. provides user option for both encryption and decryption. Marked with "?" on the TODO .
---
 TODO.md                 |  2 +-
 modules/ciphers/hill.py | 71 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 72 insertions(+), 1 deletion(-)
 create mode 100644 modules/ciphers/hill.py

diff --git a/TODO.md b/TODO.md
index 4e0f28e5..6b8b8efe 100644
--- a/TODO.md
+++ b/TODO.md
@@ -127,7 +127,7 @@
     - [ ] Caesar Cipher 
     - [ ] RSA
     - [ ] DES
-    - [ ] Hill Cipher
+    - [?] Hill Cipher
     - [ ] PlayFair Cipher
     - [ ] AES
 
diff --git a/modules/ciphers/hill.py b/modules/ciphers/hill.py
new file mode 100644
index 00000000..ba5105e1
--- /dev/null
+++ b/modules/ciphers/hill.py
@@ -0,0 +1,71 @@
+import numpy as np
+import click
+import string
+
+class HillCipher:
+    """
+    A class which implements the Hill Cipher.
+    """
+    def __init__(self, key_matrix):
+        self.key_matrix = key_matrix
+
+    def encrypt(self, message):
+        """
+        Encrypts the text using the Hill Cipher.
+        """
+        message = message.upper()
+        message = message.replace(" ", "")  # Remove spaces
+        message = [ord(char) - ord('A') for char in message]
+
+        encrypted_text = ""
+        for i in range(0, len(message), len(self.key_matrix)):
+            block = message[i:i+len(self.key_matrix)]
+            if len(block) < len(self.key_matrix):
+                # Padding if necessary
+                block += [0] * (len(self.key_matrix) - len(block))
+            block = np.array(block)
+            encrypted_block = np.dot(self.key_matrix, block) % 26
+            encrypted_text += "".join(chr(char + ord('A')) for char in encrypted_block)
+
+        return encrypted_text
+
+    def decrypt(self, message):
+        """
+        Decrypts the text using the Hill Cipher.
+        """
+        message = message.upper()
+        message = message.replace(" ", "")  # Remove spaces
+        message = [ord(char) - ord('A') for char in message]
+
+        decrypted_text = ""
+        inverse_key_matrix = np.linalg.inv(self.key_matrix)
+        determinant = int(round(np.linalg.det(self.key_matrix))) % 26
+
+        for i in range(0, len(message), len(self.key_matrix)):
+            block = message[i:i+len(self.key_matrix)]
+            if len(block) < len(self.key_matrix):
+                # Padding if necessary
+                block += [0] * (len(self.key_matrix) - len(block))
+            block = np.array(block)
+            decrypted_block = np.dot(inverse_key_matrix, block) % 26
+            decrypted_text += "".join(chr(char + ord('A')) for char in decrypted_block)
+
+        return decrypted_text
+
+# Example key matrix (3x3)
+key_matrix = np.array([[6, 24, 1], [13, 16, 10], [20, 17, 15]])
+
+hill_cipher = HillCipher(key_matrix)
+
+if __name__ == "__main__":
+    choice = click.prompt("Encrypt (e) or Decrypt (d)?")
+    message = click.prompt("Enter the message")
+
+    if choice == "e":
+        encrypted_text = hill_cipher.encrypt(message)
+        click.echo(f"Encrypted text: {encrypted_text}")
+    elif choice == "d":
+        decrypted_text = hill_cipher.decrypt(message)
+        click.echo(f"Decrypted text: {decrypted_text}")
+    else:
+        click.echo("Invalid choice")