Question

Write a Python program which implements the following two classical cryptosystem which we covered in class:

a) Affine Cipher
b) Vigenere Cipher

Answer 1

This Python program demonstrates the implementation of the Affine and Vigenère ciphers, classical encryption algorithms. The Affine Cipher uses numerical equivalents of letters and a mathematical function for encryption, while the Vigenère Cipher utilizes a keyword to determine letter shifts. Both methods underscore Python's utility in cryptography and systems programming.

Step-by-step explanation:

Python Program for Affine and Vigenère Cipher:

Learning Python is essential for implementing various algorithms such as the Affine Cipher and the Vigenère Cipher. The Affine Cipher is a type of substitution cipher where each letter in an alphabet is mapped to its numeric equivalent, encrypted using a simple mathematical function, and converted back to a letter. The Vigenère Cipher uses a keyword where each letter determines the shift for the corresponding letter in the plaintext.

Affine Cipher:

To implement the Affine Cipher in Python:

1. Define a function to encrypt text using the formula (ax + b) mod 26, where a and b are keys and x is the plaintext letter's position.
2. Define a function to decrypt text using the modular inverse of a.

Vigenère Cipher:

To implement the Vigenère Cipher in Python:

1. Use a repeated keyword to determine the shift for each letter in the plaintext.
2. Apply the shift to each letter to get the encrypted text and reverse the process to decrypt.

It's important to note that while the Affine Cipher is relatively simpler, the Vigenère Cipher provides better security due to its use of a keyword.

Both these encryption methods were significant in the historical development of cryptography but can now be easily implemented using Python, demonstrating the versatility of the language in systems programming and computer security applications. While not as secure as modern standards such as AES or RSA, these methods are valuable in understanding the basics of encryption algorithms. It also serves as an excellent educational tool for those interested in cryptography.