In this tutorial, we’ll create a Caesar Cipher tool using Python’s tkinter. By the end, you’ll have a desktop app that can encrypt and decrypt text with a shift of your choice.
We’ll break it down step by step.
Step 1: Import Required Libraries
First, we need to import the libraries:
import tkinter as tk
from tkinter import messagebox
tkinter: The standard Python library for creating GUI applications.
messagebox: Optional, used to show popup messages (like errors or alerts).
We don’t need sys or os for this app, so we can skip them.
Step 2: Define the App Theme
Let’s define some colors and fonts to make the app look modern:
# =========================
# THEME
# =========================
APP_BG = "#121212"
PANEL_BG = "#1F1F1F"
BTN_BG = "#2C2C2C"
ACCENT = "#FF6F61"
TEXT_CLR = "#E0E0E0"
SUBTEXT_CLR = "#AAAAAA"
FONT = ("Segoe UI", 11)
APP_BG: Main background color
PANEL_BG: Panel background color
BTN_BG: Button color
ACCENT: Highlight color for headers or buttons
TEXT_CLR / SUBTEXT_CLR: Colors for text and subtext
FONT: Default font for labels and buttons
This makes the app look consistent and modern.
Step 3: Create the Main App Class
We’ll create a Python class to structure our app:
class CaesarCipherApp:
def __init__(self, root):
self.root = root
root.title("MateTools – Caesar Cipher")
root.geometry("800x500")
root.configure(bg=APP_BG)
root.resizable(False, False)
root: The main Tkinter window
title(): Sets the window title
geometry(): Sets the window size
configure(bg=...): Sets background color
resizable(False, False): Prevents window resizing
Step 4: Add the Left Panel (Input & Buttons)
The left panel will hold input text, shift value, and buttons:
# Left panel
left = tk.Frame(root, bg=PANEL_BG, width=350)
left.pack(side="left", fill="y")
# Header
header = tk.Frame(left, bg=PANEL_BG)
header.pack(fill="x", padx=16, pady=(18, 10))
tk.Label(
header,
text="MateTools",
bg=PANEL_BG,
fg=ACCENT,
font=("Segoe UI", 20, "bold")
).pack(side="left")
Frame: A container to organize widgets
pack(): Places the frame on the window
Label: Shows text
fg / bg: Font and background color
We can also add a title and description:
tk.Label(left, text="Caesar Cipher Tool", bg=PANEL_BG, fg=TEXT_CLR, font=("Segoe UI", 14, "bold")).pack(anchor="w", padx=16)
tk.Label(left, text="Encrypt or decrypt text using Caesar cipher", bg=PANEL_BG, fg=SUBTEXT_CLR, font=("Segoe UI", 10)).pack(anchor="w", padx=16, pady=(0, 16))
Step 5: Add Input Fields
We need two inputs: the text to encrypt/decrypt and the shift number:
# Text input
tk.Label(left, text="Enter Text:", bg=PANEL_BG, fg=TEXT_CLR, font=FONT).pack(anchor="w", padx=16)
self.input_text = tk.Text(left, height=5, width=40, bg="#1E1E1E", fg=TEXT_CLR, font=FONT)
self.input_text.pack(padx=16, pady=(0, 10))
# Shift input
tk.Label(left, text="Shift:", bg=PANEL_BG, fg=TEXT_CLR, font=FONT).pack(anchor="w", padx=16)
self.shift_var = tk.IntVar(value=3)
tk.Entry(left, textvariable=self.shift_var, bg="#1E1E1E", fg=TEXT_CLR, font=FONT, width=5).pack(padx=16, pady=(0, 16))
Text widget: Multi-line input
Entry widget: Single-line input
IntVar(): Holds the integer shift value
Step 6: Add Buttons for Encrypt & Decrypt
We’ll create buttons and attach them to methods:
btn_frame = tk.Frame(left, bg=PANEL_BG)
btn_frame.pack(fill="x", padx=16, pady=16)
def make_btn(text, cmd, color=BTN_BG):
return tk.Button(
btn_frame,
text=text,
command=cmd,
bg=color,
fg="white",
font=("Segoe UI", 11, "bold"),
relief="flat",
height=2,
width=18
)
make_btn("Encrypt", self.encrypt_text, ACCENT).pack(side="left", expand=True, padx=4)
make_btn("Decrypt", self.decrypt_text, "#4CAF50").pack(side="left", expand=True, padx=4)
command: Links the button to a function
flat relief: Modern button style
expand=True: Makes buttons fill available space
Step 7: Add the Right Panel (Output)
The right panel will display the encrypted or decrypted text:
right = tk.Frame(root, bg=APP_BG)
right.pack(side="right", fill="both", expand=True)
self.output_card = tk.Frame(right, bg=PANEL_BG)
self.output_card.pack(padx=30, pady=40, fill="both", expand=True)
tk.Label(self.output_card, text="Output", bg=PANEL_BG, fg=TEXT_CLR, font=("Segoe UI", 14, "bold")).pack(pady=(20, 10))
self.output_text = tk.Text(self.output_card, height=10, bg="#1E1E1E", fg=TEXT_CLR, font=FONT)
self.output_text.pack(padx=16, pady=10, fill="both", expand=True)
Output text widget: Shows the result
fill="both" & expand=True: Makes the widget stretch
Step 8: Add Caesar Cipher Logic
Now we write the encryption and decryption logic:
def caesar_cipher(self, text, shift):
result = ""
for char in text:
if char.isupper():
result += chr((ord(char) - 65 + shift) % 26 + 65)
elif char.islower():
result += chr((ord(char) - 97 + shift) % 26 + 97)
else:
result += char
return result
ord(): Converts character to ASCII
chr(): Converts ASCII to character
% 26: Wraps around the alphabet
Non-alphabet characters are left unchanged
Step 9: Connect Buttons to Functions
def encrypt_text(self):
text = self.input_text.get("1.0", tk.END).strip()
shift = self.shift_var.get()
self.output_text.delete("1.0", tk.END)
self.output_text.insert(tk.END, self.caesar_cipher(text, shift))
def decrypt_text(self):
text = self.input_text.get("1.0", tk.END).strip()
shift = self.shift_var.get()
self.output_text.delete("1.0", tk.END)
self.output_text.insert(tk.END, self.caesar_cipher(text, -shift))
.get("1.0", tk.END): Gets text from the Text widget
.insert() / .delete(): Updates the output widget
Encrypt adds shift; decrypt subtracts shift
Step 10: Run the App
Finally, start the Tkinter main loop:
if __name__ == "__main__":
root = tk.Tk()
app = CaesarCipherApp(root)
root.mainloop()
Tk(): Creates the main window
mainloop(): Keeps the window running
✅ Done! You now have a complete Caesar Cipher GUI app in Python.
It looks modern, allows text input, lets the user set a shift value, and shows encrypted/decrypted output.
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