test3.py

import numpy as np

# Function to generate the key matrix
def generate_key_matrix(key, n):
    key_matrix = np.zeros((n, n), dtype=int)
    k = 0
    for i in range(n):
        for j in range(n):
            key_matrix[i][j] = ord(key[k]) % 65
            k += 1
    return key_matrix

# Function to encrypt plaintext
def hill_cipher_encrypt(plaintext, key_matrix, n):
    plaintext = plaintext.upper().replace(" ", "")
    plaintext = [ord(char) % 65 for char in plaintext]
    plaintext = np.array(plaintext)
    padding_length = n - len(plaintext) % n
    if padding_length != n:
        plaintext = np.append(plaintext, np.zeros(padding_length, dtype=int))

    ciphertext = ""
    for i in range(0, len(plaintext), n):
        block = np.array(plaintext[i:i+n])
        encrypted_block = np.dot(key_matrix, block) % 26
        ciphertext += "".join([chr(char + 65) for char in encrypted_block])

    return ciphertext

# Function to decrypt ciphertext
def hill_cipher_decrypt(ciphertext, key_matrix, n):
    inverse_key_matrix = np.linalg.inv(key_matrix)
    inverse_key_matrix = np.round(inverse_key_matrix * np.linalg.det(key_matrix)).astype(int) % 26

    decrypted_text = ""
    for i in range(0, len(ciphertext), n):
        block = np.array([ord(char) % 65 for char in ciphertext[i:i+n]])
        decrypted_block = np.dot(inverse_key_matrix, block) % 26
        decrypted_text += "".join([chr(char + 65) for char in decrypted_block])

    return decrypted_text

# Example usage
key = "GYBNQKURP"
plaintext = "HELLO"
n = 3  # Size of the key matrix (must be a perfect square)

key_matrix = generate_key_matrix(key, n)
print("Key Matrix:")
print(key_matrix)

ciphertext = hill_cipher_encrypt(plaintext, key_matrix, n)
print("Encrypted:", ciphertext)

decrypted_text = hill_cipher_decrypt(ciphertext, key_matrix, n)
print("Decrypted:", decrypted_text)