Caesar Cipher Encryption and Decryption with Python

This repository demonstrates the implementation of the Caesar Cipher encryption and decryption in Python. The Caesar Cipher is a simple substitution cipher where each letter in the plaintext is shifted by a fixed number of positions in the alphabet.

Prerequisites

There are no additional dependencies required to run this project, as it only relies on basic Python functionality. You only need Python installed on your machine.

Caesar Cipher Overview

The Caesar Cipher is one of the oldest and simplest encryption techniques. It works by shifting each letter of the plaintext by a certain number of positions in the alphabet.

• Encryption: Each letter in the plaintext is replaced by the letter that appears after it by a fixed number of positions in the alphabet (the "shift").
• Decryption: To decrypt the message, you simply shift the letters in the opposite direction by the same amount.

Code Walkthrough

Caesar Encryption

The encryption function shifts each letter of the plaintext by a specified number of positions (shift value) in the alphabet:

def caesar_encrypt(plaintext, shift):
    encrypted = ''
    for char in plaintext:
        if char.isalpha():
            shift_base = ord('A') if char.isupper() else ord('a')
            encrypted += chr((ord(char) - shift_base + shift) % 26 + shift_base)
        else:
            encrypted += char
    return encrypted

• It checks if each character is a letter.
• It calculates the shifted position by converting the character to its ASCII value (ord()), applies the shift, and converts it back to a character (chr()).
• Non-alphabetical characters (spaces, punctuation, etc.) remain unchanged.

Caesar Decryption

Decryption is simply the reverse of encryption. The same function caesar_encrypt is used with the negative shift value:

def caesar_decrypt(ciphertext, shift):
    return caesar_encrypt(ciphertext, -shift)

Example Usage

Here’s an example of how to use the Caesar Cipher functions to encrypt and decrypt a message:

plaintext = "HELLO"
shift = 3
ciphertext = caesar_encrypt(plaintext, shift)
decrypted = caesar_decrypt(ciphertext, shift)

print("Caesar Cipher - Encrypted:", ciphertext)
print("Caesar Cipher - Decrypted:", decrypted)

In this example, the plaintext message "HELLO" is encrypted with a shift of 3, resulting in the ciphertext. The ciphertext is then decrypted back to the original message using the same shift value.

Example Output

Caesar Cipher - Encrypted: KHOOR
Caesar Cipher - Decrypted: HELLO

• The plaintext "HELLO" is shifted by 3 positions to become "KHOOR".
• Decrypting "KHOOR" with the same shift (3) gives us the original message "HELLO".

How to Run the Code

1. Clone the repository:

git clone https://github.com/Jsujanchowdary/Caesar-Cipher-Encryption-and-Decryption-with-Python.git

2. Navigate to the project directory:

cd caesar-cipher-python

3. Run the script:

python caesar_cipher.py

Conclusion

This project demonstrates a simple implementation of the Caesar Cipher in Python. Although it is not secure by modern cryptographic standards, it is an excellent introductory example for understanding encryption and decryption.

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Example Directory Structure

caesar-cipher-python/
│
├── caesar_cipher.py   # Python script for Caesar Cipher encryption and decryption
├── README.md          # Project documentation
└── requirements.txt   # Python dependencies (if needed, but for this project, not required)

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Notes

• You can experiment with different shift values to see how the encryption and decryption process changes.
• The Caesar Cipher is highly vulnerable to brute-force attacks, as there are only 26 possible shifts. However, it's a good educational tool for understanding basic encryption principles.

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