Abstract:Whitenoise is a stream cipher proposed by the BSB Utilities Inc. In August 2003, Wu Hongjun proposed a breaking algorithm for Whitenoise. In this paper, the authors make an in-depth analysis for Wu’s breaking algorithm, and prove that the basic hypotheses of Wu are wrong, and that Wu’s algorithm can not find the correct key of Whitenoise. Furthermore, Wu’s algorithm is improved and a method obtaining the secret integer and the secret prime numbers is given. A forecast attack to Whitenoise is proposed, with which one can obtain signal for each clock. Furthermore, a think to obtain all the equivalent secret factors is given.