From 6239413b1cbbfad08ce5d5c2bd3ee02239030aff Mon Sep 17 00:00:00 2001
From: Nenad Balaneskovic <balaneskovic@gmx.net>
Date: Sun, 22 Jun 2025 09:05:11 +0200
Subject: [PATCH] Added a Vignere cipher class

A class for implementing a Vignere cipher (file "vignere_cipher.py") as an extension of Caesar's cipher and its README file have been added.
---
 Caesar_Cipher/Vignere_README.txt | 60 ++++++++++++++++++++++++++++++++
 Caesar_Cipher/vignere_cipher.py  | 38 ++++++++++++++++++++
 2 files changed, 98 insertions(+)
 create mode 100644 Caesar_Cipher/Vignere_README.txt
 create mode 100644 Caesar_Cipher/vignere_cipher.py

diff --git a/Caesar_Cipher/Vignere_README.txt b/Caesar_Cipher/Vignere_README.txt
new file mode 100644
index 00000000..6b354a02
--- /dev/null
+++ b/Caesar_Cipher/Vignere_README.txt
@@ -0,0 +1,60 @@
+<!--Please do not remove this part-->
+![Star Badge](https://img.shields.io/static/v1?label=%F0%9F%94%91&message=If%20Useful&style=style=flat&color=green)
+![Open Source Love](https://badges.frapsoft.com/os/v1/open-source.svg?v=103)
+
+# Vigenère Cipher: Classical Text Encryption
+
+<p align="center">
+<img src="assests/main.png" width=40% height=40%>
+
+## 🛠️ Description
+
+This script implements the **Vigenère Cipher**, a classic polyalphabetic substitution encryption technique. It accepts a keyword from the user to encode and decode messages. The same keyword must be used to decrypt the output, making it a lightweight reversible encryption tool. This is a great intro project for learning about ciphers and key-based text transformations.
+
+The script demonstrates:
+1. A `VigenereCipher` class with methods to encrypt and decrypt alphabetic strings
+2. Character-level transformation based on a repeating keyword
+3. Custom `transform()` logic that handles both encryption and decryption
+
+Feel free to enhance it with non-alphabet support, file-based encryption, or use it inside a larger pipeline.
+
+## ⚙️ Languages or Frameworks Used
+
+- Python 3.x standard library only
+- No external packages required
+
+## 🌟 How to run
+
+To execute the script, run the following in your terminal:
+
+```bash
+python vigenere_cipher.py
+```
+
+When prompted:
+- Enter a **keyword** to serve as the encryption key
+- Enter the plaintext you'd like to encrypt
+- The script will output the encrypted text and decrypt it back immediately
+
+Use `CTRL + C` to exit at any point.
+
+## 📺 Demo
+
+An example prompt might look like:
+
+```
+Enter encryption keyword: lemon
+Enter text to encrypt: hello world
+Encrypted text: siprb xbpqe
+Decrypted back: hello world
+```
+
+<img src="assests/colorgame.png" width=40% height=40%>
+
+## 🤖 Author
+
+Script by Dr. rer. nat. Nenad Balaneskovic.
+
+Nenad Balaneskovic → [GitHub Profile](https://github.com/NenadBalaneskovic)
+
+Feel free to contribute your own enhancements or port this into other encryption schemes!
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diff --git a/Caesar_Cipher/vignere_cipher.py b/Caesar_Cipher/vignere_cipher.py
new file mode 100644
index 00000000..6d5b7b8e
--- /dev/null
+++ b/Caesar_Cipher/vignere_cipher.py
@@ -0,0 +1,38 @@
+class VigenereCipher:
+    def __init__(self, keyword: str):
+        self.keyword = keyword.lower()
+        self.alphabet = 'abcdefghijklmnopqrstuvwxyz'
+
+    def shift_char(self, c, key_c, encode=True):
+        if c not in self.alphabet:
+            return c
+        shift = self.alphabet.index(key_c)
+        if not encode:
+            shift = -shift
+        return self.alphabet[(self.alphabet.index(c) + shift) % 26]
+
+    def transform(self, text: str, encode=True):
+        text = text.lower()
+        result = []
+        key_len = len(self.keyword)
+        for i, c in enumerate(text):
+            key_c = self.keyword[i % key_len]
+            result.append(self.shift_char(c, key_c, encode))
+        return ''.join(result)
+
+    def encrypt(self, text: str) -> str:
+        return self.transform(text, True)
+
+    def decrypt(self, text: str) -> str:
+        return self.transform(text, False)
+
+if __name__ == "__main__":
+    keyword = input("Enter encryption keyword: ").strip()
+    cipher = VigenereCipher(keyword)
+
+    plaintext = input("Enter text to encrypt: ").strip()
+    encrypted = cipher.encrypt(plaintext)
+    print(f"Encrypted text: {encrypted}")
+
+    decrypted = cipher.decrypt(encrypted)
+    print(f"Decrypted back: {decrypted}")
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