Implementing a Simple Data Encryption Algorithm Using Caesar Cipher in Python

Goal : Understand the basic concepts of data encryption and implement a simple encryption algorithm.

Learning Content : Data encryption is the process of converting plaintext into ciphertext to prevent unauthorized access. Differential privacy is a technique that adds noise to data to protect individual privacy.

Practice : We will implement a Caesar Cipher, a basic symmetric substitution cipher, in Python. No external libraries are required.

Step 1 – Install Required Libraries : Ensure Python is installed; the implementation uses only the standard library.

Step 2 – Implement Caesar Cipher Encryption :

def caesar_cipher_encrypt(text, shift):
    """Encrypt text using Caesar Cipher.
    Args:
        text (str): plaintext to encrypt
        shift (int): number of positions to shift each letter
    Returns:
        str: ciphertext
    """
    encrypted_text = ""
    for char in text:
        if char.isalpha():  # letter
            shift_amount = shift % 26  # only 26 letters
            if char.islower():
                new_char = chr(((ord(char) - ord('a') + shift_amount) % 26) + ord('a'))
            else:
                new_char = chr(((ord(char) - ord('A') + shift_amount) % 26) + ord('A'))
        else:
            new_char = char  # non‑letter characters unchanged
        encrypted_text += new_char
    return encrypted_text

Step 3 – Implement Caesar Cipher Decryption :

def caesar_cipher_decrypt(cipher_text, shift):
    """Decrypt Caesar Cipher ciphertext.
    Args:
        cipher_text (str): ciphertext to decrypt
        shift (int): number of positions originally shifted
    Returns:
        str: original plaintext
    """
    decrypted_text = ""
    for char in cipher_text:
        if char.isalpha():
            shift_amount = shift % 26
            if char.islower():
                new_char = chr(((ord(char) - ord('a') - shift_amount) % 26) + ord('a'))
            else:
                new_char = chr(((ord(char) - ord('A') - shift_amount) % 26) + ord('A'))
        else:
            new_char = char
        decrypted_text += new_char
    return decrypted_text

Step 4 – Full Example with Testing :

# Define both functions (see above)

plain_text = "你好，世界！Hello, World!"
shift = 3  # shift by 3 positions

# Encryption
encrypted_text = caesar_cipher_encrypt(plain_text, shift)
print(f"明文: {plain_text}")
print(f"密文: {encrypted_text}")

# Decryption
decrypted_text = caesar_cipher_decrypt(encrypted_text, shift)
print(f"密文: {encrypted_text}")
print(f"解密后的明文: {decrypted_text}")

Step 5 – Run the Code : Save the script as caesar_cipher.py and execute python caesar_cipher.py from the command line. Expected output:

明文: 你好，世界！Hello, World!
密文: 你好，世界！Khoor, Zruog!
密文: 你好，世界！Khoor, Zruog!
解密后的明文: 你好，世界！Hello, World!

Summary : After completing this practice you should understand how a simple symmetric encryption algorithm works. While Caesar Cipher is educational, real‑world applications use stronger algorithms such as AES for higher security.