add: vigenere cipher

Good cipher algorithm named vigenere implemented in Python Programming Language.

Author: NitkarshChourasia

Diff for: vigenere_cipher.py

@@ -0,0 +1,39 @@
+text = "mrttaqrhknsw ih puggrur"
+custom_key = "happycoding"
+
+
+def vigenere(message, key, direction=1):
+    key_index = 0
+    alphabet = "abcdefghijklmnopqrstuvwxyz"
+    final_message = ""
+
+    for char in message.lower():
+        # Append any non-letter character to the message
+        if not char.isalpha():
+            final_message += char
+        else:
+            # Find the right key character to encode/decode
+            key_char = key[key_index % len(key)]
+            key_index += 1
+
+            # Define the offset and the encrypted/decrypted letter
+            offset = alphabet.index(key_char)
+            index = alphabet.find(char)
+            new_index = (index + offset * direction) % len(alphabet)
+            final_message += alphabet[new_index]
+
+    return final_message
+
+
+def encrypt(message, key):
+    return vigenere(message, key)
+
+
+def decrypt(message, key):
+    return vigenere(message, key, -1)
+
+
+print(f"\nEncrypted text: {text}")
+print(f"Key: {custom_key}")
+decryption = decrypt(text, custom_key)
+print(f"\nDecrypted text: {decryption}\n")