However , this comes at a cost : because the keystream is now pseudorandom , and not truly random , the proof of security associated with the one-time pad no longer holds : it is quite possible for a stream cipher to be completely insecure .

However , because the keystream is pseudorandom , and not truly random , the security associated with the one-time pad can not be applied and it is quite possible for a stream cipher to be completely insecure .
