低速率分布式拒绝服务(LDDoS,low-rate distributed denial of service)攻击是一种新型的DDoS攻击方式。LDDoS具有流量小和隐蔽性强的特点,现有的DDoS攻击检测方法不能正确发现LDDoS攻击流量。根据LDDoS攻击流量呈现周期性的特点,采用缓存队列占有率统计的方法,重点研究了受害目标路由器的缓存队列,分别统计分析了正常和攻击流量的占有率,并在NS-2环境中进行了仿真实验,成功提取了LDDoS攻击流量上的2个特征,提高了LDDoS攻击的检测率。
This paper presents a hierarchy model of Air Traffic Management (ATM) according to the security requirements in ATM system, analyzes it by grey assessment and Analytic Hierarchy Process (AHP), and evaluates it in details. It also provides theoretical support for building an effective evaluation system. The basic idea is to use AHP and Grey Assessment to obtain the weights of the indicators, and count grey evaluation coefficients with whitening function. The compositive clustering coefficients are obtained by combining the weights and the grey evaluation coefficients. Evaluation result can be gotten from the compositive clustering coefficients.
Information hiding techniques adopted in secret communication should meet the requirements of high hiding capacity,real-time and high robustness.For the purpose of real-time speech secure communication,an information hiding algorithm based on the analysis-by-synthesis（ABS） speech coding scheme is presented in this article.This algorithm substitutes secret speech data bits for linear predictive coefficients（LPCs） in linear predictive coding（LPC）.Statistics show that the change of voiced signal track is slow and the codebook for LPCs vector is large in ABS coding scheme.Therefore,a new concept,filter similarity,is proposed to determine the LPC parameters for substituting with secret speech information,and to generate multi-codebook for saving storage space to store secret speech information.To achieve the best effects of information hiding,a dynamic threshold is built to make an optimal trade-off among hiding-capacity,security,robustness,transparence and real time.Experiments show that the proposed approach meets the requirements of information hiding and secret communication speech quality.The test results indicate that this approach reaches high hiding capacity with an excellent speech quality and complicating speakers＇ recognition.
