Instructions:
	1. The 16-byte hex you want to encrypt is in file 'testBlock'.
	2. The key for this encryption is in file 'testKey'. Key is 32 byte hex.
	3. To encrypt run -
		python main.py encrypt
		--- Encrypted text gets written in file 'encrypted_file'
	4. To decrypt run -
		python main.py decrypt
		--- Decrypted text gets written in file 'decrypted_file'