'Creates the cipher-related objects needed for AES-CTR
encryption and decryption.'

def initialize_cipher(self):

    self.ctr_e = Counter.new(self.AES_block_size, initial_value=self.iv)
    self.ctr_d = Counter.new(self.AES_block_size, initial_value=self.iv)
    self.encryptor = AES.new(self.key, AES.MODE_CTR, counter=self.ctr_e)
    self.decryptor = AES.new(self.key, AES.MODE_CTR, counter=self.ctr_d)
