solves multiplicative cipher

README.md

@@ -21,7 +21,7 @@ Algorithms from the book Cryptography & Network Security ~Behrouz A. Forouzan. S
 ## 🔑 [Traditional Symmetric Key Ciphers](notebooks/3-symmetric-key-ciphers.ipynb)
 1. Monoalphabetic Ciphers
     1. [Caesar Shift Cipher](ciphers/CaesarShiftCipher.py)
-    1. Multiplicative Cipher
+    1. [Multiplicative Cipher](ciphers/MultiplicativeCipher.py)
     1. Affine Cipher
 1. Polyalphabetic Ciphers
     1. Autokey Cipher

ciphers/MultiplicativeCipher.py

@@ -0,0 +1,23 @@
+from mathematics import multiplicative_inverse
+
+
+class MultiplicativeCipher:
+    def __init__(self, key):
+        self.key = key
+
+    def encrypt(self, plaintext: str) -> str:
+        return ''.join([self.num_2_char((self.char_2_num(letter) * self.key) % 26) for letter in plaintext.lower()])
+
+    def decrypt(self, ciphertext: str) -> str:
+        return ''.join(
+            [self.num_2_char((self.char_2_num(letter) * multiplicative_inverse(self.key, 26)) % 26)
+             for letter in ciphertext.lower()]
+        )
+
+    @staticmethod
+    def char_2_num(character: str) -> int:
+        return ord(character.lower()) - ord('a')
+
+    @staticmethod
+    def num_2_char(number: int) -> str:
+        return chr(number + ord('a'))

ciphers/__init__.py

@@ -2,3 +2,4 @@
 from ciphers.VignereCipher import VignereCipher
 from ciphers.PlayfairCipher import PlayFairCipher
 from ciphers.CaesarShiftCipher import CaesarShiftCipher
+from ciphers.MultiplicativeCipher import MultiplicativeCipher

test.py

@@ -1,6 +1,6 @@
-from ciphers import CaesarShiftCipher
+from ciphers import MultiplicativeCipher
 
-caesar_cipher = CaesarShiftCipher(10)
+caesar_cipher = MultiplicativeCipher(7)
 ciphertext = caesar_cipher.encrypt('helloworld')
 print(ciphertext)
 print(caesar_cipher.decrypt(ciphertext))