Abstract: The paper focuses on the correlation property of the combiners with memory.Using the hidden Markov model，a formula is given to compute directly the conditional probability of the memory state.Under some other conditions，we pay special attention to the usage of the formula in detail.Based on the conclusions obtained above，a conditional correlation attack is given to the improved summation generator.The comparisons with other attacks show that our attack offers good trade-off between the complexity and the required key stream length.

摘要： 利用隐马尔可夫模型对带记忆组合生成器概率模型的相关性问题进行了研究，得到快速计算记忆状态条件概率的公式。讨论了上述计算公式在限定条件下的应用。在此基础上对改进的加法生成器进行了条件相关攻击，与其它攻击方法相比，条件相关攻击的计算复杂度和所需密钥流长度达到了折中。