  The internal state of the Klimov-Shamir number generator TF-1 consists of
four words of size w bits each, whereas its intended strength is 2^{2w}. We
exploit an asymmetry in its output function to show that the internal state can
be recovered after having 2^w outputs, using 2^{1.5w} operations. For w=32 the
attack is practical, but for their recommended w=64 it is only of theoretical
interest.
