Caesar Cipher

A simple Python implementation of the Caesar cipher, a substitution cipher that encrypts text by shifting each letter through the alphabet.

Features

• Encrypts and decrypts text using a configurable shift.
• Preserves uppercase and lowercase letters.
• Leaves spaces, punctuation, numbers, and other non-alphabetic characters unchanged.
• Validates the shift value (an integer from 1 to 25).

Requirements

• Python 3
• No external dependencies

Getting Started

1. Clone or download this repository.

2. Save the code in a Python file, for example caesar_cipher.py.

3. Run it from your terminal:

   python caesar_cipher.py

Usage

from caesar_cipher import encrypt, decrypt

message = "Hello, World!"

encrypted = encrypt(message, 3)
print(encrypted)  # Khoor, Zruog!

decrypted = decrypt(encrypted, 3)
print(decrypted)  # Hello, World!

You can also use the main caesar() function directly:

from caesar_cipher import caesar

print(caesar("Hello, World!", 3))                 # Khoor, Zruog!
print(caesar("Khoor, Zruog!", 3, encrypt=False))   # Hello, World!

Replace caesar_cipher with the name of your Python file if it is different.

How It Works

Each letter is mapped to a letter a fixed number of positions away in the alphabet. For example, with a shift of 3, A becomes D, B becomes E, and X becomes A.

Decryption applies the same process in the opposite direction. The implementation uses Python's str.translate() and str.maketrans() to perform the character substitution.

Input Validation

The shift must be an integer between 1 and 25, inclusive. Invalid values return an explanatory error message.

Security Note

The Caesar cipher is intended for learning about classical cryptography, not for protecting sensitive information. Its small key space makes it easy to break.