1. Importing Libraries

import tkinter as tk
from tkinter import messagebox

• tkinter: For building the graphical user interface (GUI).

• messagebox: For showing error or info messages (e.g., invalid input).

2. Caesar Cipher Functions

🔸 Encrypt Function

def encrypt(text, shift):
    result = ""
    for char in text:
        if char.isalpha():  # Only encrypt letters
            base = ord('A') if char.isupper() else ord('a')  # Maintain case
            result += chr((ord(char) - base + shift) % 26 + base)
        else:
            result += char  # Keep spaces, punctuation unchanged
    return result

🔸 Decrypt Function

def decrypt(text, shift):
    return encrypt(text, -shift)

• Uses the same encrypt() function but with the opposite shift to reverse the encryption.

3. GUI App Initialization

def launch_app():

Encapsulates the entire Tkinter app in one function so it can be called easily.

4. Encrypt Button Functionality

def encrypt_message():
    msg = message_entry.get()  # Get message from user input
    try:
        shift = int(key_entry.get())  # Get shift key and convert to integer
        encrypted = encrypt(msg, shift)
        result_var.set(f"Encrypted: {encrypted}")
    except:
        messagebox.showerror("Invalid", "Shift must be an integer.")

• Takes user input and shift key, runs the encryption, and shows result.

• If shift is not an integer, it shows an error popup.

5. Decrypt Button Functionality

def decrypt_message():
    msg = message_entry.get()
    try:
        shift = int(key_entry.get())
        decrypted = decrypt(msg, shift)
        result_var.set(f"Decrypted: {decrypted}")
    except:
        messagebox.showerror("Invalid", "Shift must be an integer.")

• Same as encrypt but uses the decryption function.

6. GUI Layout

app = tk.Tk()
app.title(" Cryptography App - Caesar Cipher")
app.geometry("400x300")

• Creates the main window with title and size.

🔹 Message Input

tk.Label(app, text="Enter Message:").pack()
message_entry = tk.Entry(app, width=40)
message_entry.pack(pady=5)

🔹 Shift Key Input

tk.Label(app, text="Enter Shift Key:").pack()
key_entry = tk.Entry(app, width=10)
key_entry.pack(pady=5)

🔹 Buttons for Action

tk.Button(app, text="Encrypt", command=encrypt_message).pack(pady=5)
tk.Button(app, text="Decrypt", command=decrypt_message).pack(pady=5)

🔹 Output Display

result_var = tk.StringVar()
tk.Label(app, textvariable=result_var, font=("Arial", 12), fg="blue").pack(pady=10)

7. Run the App

app.mainloop()

• Starts the GUI loop, waits for user interaction.

Final Call to Launch

launch_app()

• Calls the function to launch the GUI.

 What It Does

• Accepts text and a numeric shift key from the user.

• Encrypts or decrypts using the Caesar Cipher.

• Shows the result in the GUI.

• Handles invalid input with error messages.