组合生成器的多线性相关攻击

本文对组合生成器提出了一种相关攻击方法,这种方法同时利用组合生成器输入与输出之间多个线性关系的信息来恢复密钥,我们从理论上证明了该方法可有效的减少攻击所需的数据量.特别地,我们将这种方法用于攻击"蓝牙组合生成器",使攻击复杂度得到显著降低.     

带记忆多值组合生成器的相关免疫性

考察带l位记忆多值组合生成器输入序列和输出序列的相关免疫性以及k阶相关免疫组合函数的构造。     

一类钟控组合生成器的符合率

给出3个停走生成器在模2加组合方式下符合率的有关结论。此类生成器的输出序列与相应停走生成器的控制序列相互独立;输出序列与相应停走生成器的目标LFSR输出序列不独立,本文对输出序列与目标LFSR序列的符合率进行了讨论,给出有限维联合分布的计算公式。     

联合的F-FCSR密钥流生成器

 在分析带进位反馈移位寄存器(FCSR)的滤波密钥流生成器族F-FCSR线性弱点和其硬件方案F-FCSR-Hv2被攻破原因基础之上,提出了利用两个F-FCSR输出简单非线性运算而成的联合的F-FCSR密钥流生成器.该生成器避免了利用该种情况而进行的Hell-Johansson攻击,其生成序列通过了美国技术与标准局(NIST)STS的16项随机性测试,有高的复杂度,且能抵抗相关攻击和代数攻击.     

基于FCSR的双滤波密钥流生成器

当前,由于还没有一个适于一般目的的流密码国际加密标准,流密码的设计与分析引起了广泛关注。在以前的流密码的设计中多采用线性反馈移位寄存器（LFSR）作为基本的部件。然而由于LFSR本身的线性性,基于LFSR的流密码备受攻击,进而相继出现了一些替换部件,例如T函数,带进位的反馈移位寄存器（FCSR）等等。文中给出了一个新的基于FCSR的密钥流生成器。理论分析表明该密钥流生成器具有高度的安全性。NIST统计测试表明该密钥流生成器的伪随机特性是理想的。     

一类具有可控线性复杂度和双重密钥的非线性生成器

本文讨论一类非线性生成器的分析与综合。这类非线性生成器由三部份组成:nm级的带有本原联结多项式的线性移位寄存器,随机选择器;m端的非线性前馈函数。本文证明了该系统的线性复杂度是可控制的;易于实现(其软件实现的计算复杂度为O(m~3+nm));安全性远远高于原始的前馈网络,即在已知前馈函数和线性移位寄存器时,破译该系统穷举法成功的概率几乎为零。     

一种A5流密码算法的设计实现

A5算法是一种利用伪随机数和非线性运算实现的流密码,它是求和生成器和钟控移位寄存器的组合,其线性复杂度大于两种生成器线性复杂度,加密速度快,适合无线突发信道。     

多值“加法型”组合生成器分析

文中运用信息论原理对多值“加法型”组合生成器序列进行分析，得到钟控序列与输出序列的互信息为零的结论，证明了钟控输入与输出序列之间互信息是输出序列长度的严格递增函数，进而对控选逻辑序列设计进行分析。     

GPS中频信号生成器的FPGA设计

介绍了一种GPS中频信号生成器的设计,利用了Xilinx公司的microblaze软核技术,生成器的核心部分在一块FPGA内部实现.降低了电路设计的复杂性以及实现成本,并且使得系统更具灵活性和扩展性.将详细描述生成器核心部分中microblaze系统的搭建以及关键逻辑电路的设计,最后给出生成器输出中频信号的频谱分析结果,并使用GPS接收机对上变频后的信号进行了接收测试.     

干涉合成孔径雷达的垂直基线对图像相干性的影响

 本文指出了InSAR中垂直基线是影响图像相干性的重要因素,论证了现有的直接计算相关系数的公式是基于理想信号得出的,然后结合实际雷达信号的频率特性推导出了一个直接计算相关系数的公式,并给出了在各种斜坡地形情况下相关系数与垂直基线的变化关系.这种计算方法及其数值结果可用于对干涉合成孔径雷达的基线设计和性能评估.     

Correlation properties of a general binary combiner with memory

Correlation properties of a general binary combiner with an arbitrary number M of memory bits are derived and novel design criteria proposed. For any positive integer m, the sum of the squares of the correlation coefficients between all nonzero linear functions of m successive output bits and all linear functions of the corresponding m successive inputs is shown to be dependent upon a particular combiner, unlike the memoryless combiners. The minimum and maximum values of the correlation sum as well as the necessary and sufficient conditions for them to be achieved are determined. It turns out that the security of combiners with memory can be considerably improved if M is not small.An efficient linear sequential circuit approximation (LSCA) method is developed for obtaining output and input linear functions with comparatively large correlation coefficients which is feasible for large M and works for any practical scheme. The method consists in deriving and solving a linear sequential circuit with additional nonbalanced inputs that is based on linear approximations of the output and the component next-state functions. The corresponding correlation attack on combiners with linear feedback shift registers is analyzed and it is shown that every such combiner with or without memory is essentially zero-order correlation immune.A preliminary version of this paper was presented at Eurocrypt '92 and was published in the proceedings. This research was supported in part by the Science Fund of Serbia, Grant #0403, through the Institute of Mathematics, Serbian Academy of Arts and Sciences.     

Optimal diversity combining under correlated noise in mobile radio

In this paper the performance of predetection maximal ratio and equal gain combiners are investigated under conditions of correlated branch noise. A statistical model is devised to determine the spatial noise correlation coefficients at metropolitan‐area base stations, and the cases where significant correlation is likely are clarified. Optimal weighting coefficients for a maximal ratio combiner with two‐branch space diversity are derived under correlated noise. Based on this result it is shown that correlation in branch noise can be used to improve the combiner performance by dynamically adjusting the weightings so as to partially cancel the noise. Performance of equal gain combiners is also shortly discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

一类基于时变逻辑的序列发生器

基于带记忆组合逻辑的序列发生器虽然抗传统的相关攻击,但易受线性时序电路逼近攻击.结合表更新的思想,本文给出了一类基于时变逻辑的序列发生器模型,并分析了输入输出间的相关性等密码学性质.许多密码体制都可归于此种模型,该模型对设计序列发生器有借鉴意义.     

Edit distances and probabilities for correlation attacks onclock-controlled combiners with memory

A theoretical framework for correlation attacks based on edit distances and edit probabilities on binary keystream generators consisting of clock-controlled shift registers combined by a function with memory is introduced. Recursive algorithms for efficient computation of the proposed many-to-one string edit distances and statistically optimal edit probabilities are derived for both constrained and unconstrained irregular clocking. The distances and probabilities are based on mutually correlated linear transforms of input and output sequences in the corresponding regularly clocked combiner with memory. Linear transforms can also incorporate linear models of clock-controlled shift registers. The complexity of the recursive algorithms is exponential in the memory size of the input linear transform which can be considerably smaller than the memory size of combining function. This is demonstrated for a special type of combiners with memory based on a time-varying memoryless function. In addition, a decimation method for reducing the memory size of the input linear transform is proposed. The design criteria with respect to the introduced correlation attacks are also discussed     

Conditional correlation attack on combiners with memory

A connection between linear codes and the correlation attack conditioned on the output of binary combiners with memory is established. Using a sort of random coding argument, it is shown that an average combiner with memory is potentially vulnerable to such an attack only if the number of outputs is equal to or greater than the number of inputs. The required computational complexity in the former case is exponentially greater than in the latter case     

Optimization of Linear Cooperation in Spectrum Sensing Over Correlated Log-normal Shadow Fading Channels

The objective of cooperative spectrum sensing is to collaboratively detect the presence of the primary user by the aid of multiple secondary users. It is known that the performance of such a framework substantially depends on the fading assumption. In this paper, we propose an advanced framework for linear cooperative spectrum sensing in cognitive radio networks over correlated log-normal shadow fading channels. Considering the realistic sensing and reporting channels which are not addressed in similar works, motivates us to propose a novel approximation for correlated log-normal sum based on moment generating function calculation and moment matching method. Furthermore, the linear cooperative spectrum sensing coefficients are computed based on the optimization of the deflection criterion. This results in a framework with reasonable complexity which is suitable for practical applications. Simulation results show the excellent agreement between the exact and approximated statistics and the superior performance compared with conventional equally gain combiner.     

Correlation properties of combiners with memory in stream ciphers

For pseudo-random generators where one or several LFSRs are combined by a memoryless function, it is known that the output sequences are correlated to certain LFSR-sequences whose correlation coefficients c _t satisfy the equation _i c ₂ ⁱ = 1. In this paper it is proved that a corresponding result also holds for generators whose LFSRs are connected to a combiner with memory.If correlation probabilities are conditioned on side information, e.g., on known output digits, it is shown that new or stronger correlations may occur. This is exemplified for the summation cipher with only two LFSRs where such correlations can be exploited in a known plaintext attack. A cryptanalytic algorithm is given which is shown to be successful for LFSRs of considerable length and with arbitrary feedback connection.A preliminary version of this paper was presented at Eurocrypt '90, May 21–24, Århus, Denmark, and has appeared in the proceedings, pp. 204–213.     

Computation of external circuit impedance of active devices in amillimeter wave harmonic power combiner

In this note, the external circuit impedance looking outside from two active devices, which are abreast mounted in the rectangular waveguide cavity of a millimeter wave harmonic power combiner, are analyzed and computed by strict field analysis method and the technique uniting Galerkin method with Collocation method. The numerical results are very useful to design the millimeter wave harmonic power combiner and develop its CAD     

Design of grating-assisted waveguide couplers with weightedcoupling

The design of grating-assisted, channel waveguide codirectional couplers is demonstrated using the Gel'fand-Levitan-Marchenko inverse scattering method. Weighted coupling coefficients are computed from rational expression for the desired wavelength response. Approximate formulas that relate the waveguide and grating geometries to the computed coupling coefficients are derived. The technique is illustrated by designing a directional coupler with a third-order Butterworth filter characteristic and a 130 Å full-width-half-maximum bandwidth     

高功率非对称泵浦耦合器理论研究

高功率非对称泵浦耦合器是高功率连续光纤激光器的关键无源光器件,它可以将多路泵浦光高效率地耦合进主光纤中,从而为光纤激光器提供所需的泵浦光功率,但已有双波导耦合理论并不能直接应用于该型耦合器的研究。为解决这一问题,在双波导定向耦合器的不完全耦合理论基础上,针对高功率泵浦耦合器非对称的特点,将其耦合系数和光功率方程组做了进一步推导,并进行了数值仿真,研究结果表明:两光纤中的光功率按照一定周期变化,当泵浦光纤的锥角在1~1.5之间时,可以获得97%以上的最佳耦合效率,且与其对应耦合长度的局部变化对耦合效率的影响较小。该研究结果对高功率非对称泵浦耦合器的设计及制作均具有指导意义。