Add demo files

demo.py

+from key_generator import KeyGenerator
+from pem_converter import PEMConverter
+from rsa_encryptor import RSAEncryptor
+
+def demo():
+    print("=== RSA DEMO ===")
+    
+    # [1] Key generation
+    key_generator = KeyGenerator(bits=512)
+
+    ## Generate a private key 
+    private_key = key_generator.generate_private_key()
+    ## Generate a public  key 
+    public_key = key_generator.extract_public_key(private_key)
+    
+    print("Private Key:", private_key)
+    print("Public Key:", public_key)
+
+    # [2] Convert to PEM format
+
+    pem_converter = PEMConverter() # defin pem formater 
+
+    private_pem = pem_converter.to_pem(private_key, "PRIVATE") # format the priavte key
+    public_pem = pem_converter.to_pem(public_key, "PUBLIC") # format the publiie key
+
+    print("\nPrivate Key (PEM):\n", private_pem)
+    print("\nPublic Key (PEM):\n", public_pem)
+
+    # [3] Encrypt and decrypt a message
+    
+    ## Creata an Encrpytor
+    rsa_encryptor= RSAEncryptor()
+    message = "\n\nHello, RSA!"
+    print("\nOriginal Message:", message)
+
+    encrypted_message = rsa_encryptor.encrypt(message, public_key)
+    print("Encrypted Message:", encrypted_message)
+
+    decrypted_message = rsa_encryptor.decrypt(encrypted_message, private_key)
+    print("Decrypted Message:", decrypted_message)
+    
+    # [4] Convert PEM back to keys
+    restored_private_key = pem_converter.from_pem(private_pem)
+    restored_public_key = pem_converter.from_pem(public_pem)
+
+    # [5] Verify decryption with restored keys
+    print("\nVerifying decryption with restored keys...")
+    decrypted_with_restored = rsa_encryptor.decrypt(encrypted_message, restored_private_key)
+    print("Decrypted Message with Restored Key:", decrypted_with_restored)
+
+if __name__ == "__main__":
+    demo()