  This paper presents how to make use of the advantage of round-off error
effect in some research areas. The float-point operation complies with the
reproduce theorem without the external random perturbation. The computation
uncertainty principle and the high nonlinear of chaotic system guarantee the
numerical error is random and departure from the analytical result. Combining
these two properties we can produce unilateral one-way function and provide a
case of utilizing this function to construct encryption algorithm. The
multiple-precision (MP) library is used to analyze nonlinear dynamics systems
and achieve the code. As an example, we provide a scheme of encrypting a
plaintext by employing the one-way function with Lorenz system. Since the
numerical solution used in this scheme is beyond the maximum effective
computation time (MECT) and it cannot satisfy the requirements of return-map
analysis and phase space reconstruction, it can block some existing attacks.
