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为了促进可证安全性在密码学中的应用,我们对基于分组密码算法验证模式的单向函数进行了证明。认证模式是分组密码算法五种工作模式标准化新加入的一种,通过这一工作"教科书式密码"转化为现实的分组密码算法。通过安全性证明:分组密码算法的验证运算模式因为算法本身的强度而使得消息在保密和认证两方面都具备了可用的理论基础,是构造单向函数的一种合适的方法。 相似文献
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利用通信双方密码设备的身份特征和共享密钥,提出了一种基于身份认证的密钥协商模型,采用与时间戳机制相绑定的分组密码算法、杂凑算法加密体制,定义了密码设备进行密钥协商的工作流程,按此流程进行双方通信密钥的按需协商以及共享密钥的实时有效更新,保证了密钥协商过程的机密性、完整性、防重放性和不可预测性,为某些应用模式下密码设备的安全密钥交换提供了一种有效实用的技术手段。 相似文献
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分组算法模块的VHDL和VERILOG实现及其比较研究 总被引:1,自引:1,他引:0
分组密码算法是一种常用的密码技术.其加密速度非常快,在数据加密领域仍广泛使用.目前,分组密码的重点研究方向包括新型分组密码的研究,分组密码的实现研究,分组密码的各个组件的研究等等.本文从AES的5个候选算法中提炼出7大分组算法模块,分别用VHDL和Verilog实现,并对资源占用情况加以分析比较.然后选取分组算法的典型代表AES,用两种语言实现并对资源占用情况和实现速率加以比较.结果表明:对于小型分组算法模块,VHDL和Verilog的实现在占用逻辑单元方面基本上没有什么差别;对较为复杂的模块和AES算法,Verilog的实现会比VHDL的实现占用较少的资源,但速度要慢些. 相似文献
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BMP图像加密算法研究 总被引:1,自引:0,他引:1
流密码与分组密码是基于位运算的图像加密算法中两种主要密码体制。着重研究了分组密码长度和密码多样性的不同选取对加密BMP彩色图像的影响。指出了在分组密码长度与BMP图像的长宽尺寸成倍数关系的情况下,BMP图像加密效果极其不理想的规律和现象,并对此进行了分析和研究。此外,对采用基于位运算方法加密BMP图像的抗噪声性能也进行了分析。 相似文献
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分组密码的应用非常广泛,但由于差分密码攻击和线性密码攻击的出现,使分组密码受到致命的打击,文章基于能够保护已有软件和硬件使用分组密码投资的目的,采用多重加密的思想,通过对密码体制强化的方法,提出了一个新的三重加密方案,并分析了其安全性特征,得到了安全性更强的一种算法。 相似文献
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2001年11月,NIST确定新的加密算法Rijndael为高级加密标准(AES),以取代安全性已经不能满足需要的的原数据加密标准(DES)。AES属于对称分组密码,可用128、192、256位密钥对128位的分组明文明文行加解密。本文在分析其算法结构和性能特点的基础上,作出了具体的设计实现。 相似文献
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介绍并讨论了一种逻辑加密卡安全体系实现的设计方法,针对加密卡成本较低、使用方便、安全性较好、用途广泛等要求,提出了包括密码认证体系和写保护体系在内的安全系统,给出了密码认证过程的几种模拟结果 相似文献
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提出了一种实用的分组密码工作模式NOTP(Nearly One-Time Pad),即分组密码的拟一次一密工作模式。该模式不仅可以提供理想的安全强度,还可提供完整性和认证性。NOTP具备了CBC工作模式的所有优点,而且在安全性和运算效率方面更加优越,因此,它在很多方面优于CBC工作模式。 相似文献
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高功率横流CO2激光横模随时间变化的测量 总被引:2,自引:4,他引:2
用激光光束分析仪实时在线测量了一台连续运转的高功率横流CO2激光器的激光横模,获得了较为完整的激光横模随时间的变化关系.测量结果表明,激光输出由两个分离的、非对称的高阶横模叠加组成("双模"),两横模中心相距约8 mm.形成"双模"的原因是串接式谐振腔的前腔和后腔两者的中心轴线不重合以及阴极铜管形变.横模随激光器运行时间的延长而逐步蜕化,呈更高阶和复杂化趋向.初步分析表明,横模的时间变化主要与激光器连续运转过程中腔内气体组分发生的变化有关. 相似文献
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Mechanisms which determine the oscillating transverse and longitudinal modes in semiconductor injection lasers are discussed in this paper. The analysis is based on the semiclassical method in which the optical field is represented by Maxwell equations and the lasing phenomenon is analyzed quantum mechanically using the density matrix formalism. Guided modes are classified by the relation between refractive index and gain-loss differences at the boundaries of the active region as normal guided mode (index guiding), active-guided mode (gain guiding), and leaky mode (anti-index guiding). The guiding loss and cutoff conditions are given for these modes. The optimum range to obtain stable fundamental transverse mode operation is discussed with respect to several guiding factors, such as width of active region, the refractive index difference, and gain-loss differences at the boundaries of the active region. Longitudinal mode behavior is discussed in terms of electron transition mechanism in semiconductor crystals. The relaxation effect of the electron wave is introduced in this model. Profiles of the saturated gain and the spatial diffusion of the electron are related to this relaxation effect. Mode competition phenomena are analyzed, and a strong gain suppression among the longitudinal modes is shown to be as an intrinsic property of semiconductor lasers. The possibility of obtaining single longitudinal mode operation is postulated. Physical influences for stable single longitudinal mode operation are discussed in terms of transverse mode control (or stripe structure), spontaneous emission, threshold current level, impurity concentration in the active region, and direct modulation. Some experimental results are also given to support these analyses. 相似文献
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This letter concerns the mode-competition effect for compound-cavity lasers. Considering the mode properties of such a system we show, that the side cavity mode having the same threshold gain as the lasing one, may correspond to either stable or unstable modes of laser operation. In the last case the mode competition leads to locking of the lasing and side modes yielding high-frequency self-pulsations in some range of the system parameters. This effect can be used for the design of self-pulsating SLs generating optical pulses in the microwave region without an intracavity saturable absorber 相似文献
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Eli Biham 《Journal of Cryptology》1998,11(1):45-58
In recent years, several new attacks on DES were introduced. These attacks have led researchers to suggest stronger replacements
for DES, and in particular new modes of operation for DES. The most popular new modes are triple DES variants, which are claimed
to be as secure as triple DES. To speed up hardware implementations of these modes, and to increase the avalanche, many suggestions
apply several standard modes sequentially. In this paper we study these multiple (cascade) modes of operation. This study shows that many multiple modes are much weaker than multiple DES, and their strength
is theoretically comparable to a single DES.
We conjecture that operation modes should be designed around an underlying cryptosystem without any attempt to use intermediate
data as feedback, or to mix the feedback into an intermediate round. Thus, in particular, triple DES used in CBC mode is more
secure than three single DESs used in triple CBC mode. Alternatively, if several encryptions are applied to each block, the
best choice is to concatenate them to one long encryption, and build the mode of operation around it.
Received 15 February 1996 and revised 30 May 1996 相似文献
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提出了一种具有对称结构的大模场面积和低弯曲损耗的新型结构光纤,运用全矢量有限元法结合完美匹配层边界条件分析了光纤特性。该光纤由纤芯中的梯形折射率环和包层中的多层下陷层组成,仿真结果显示该光纤具有低弯曲损耗大模场单模传输的特性。对比分析了梯形谐振环、矩形谐振环、三角形谐振环结构光纤的弯曲损耗以及电场模式分布,实验结果显示梯形折射率环更具优越性。多层下陷层结构将模场限制在纤芯中,下陷层的数量大于2时模场面积基本上保持不变。研究结果表明,在波长为1 550 nm、弯曲半径为20 cm时,基模(FM)弯曲损耗只有0.056 868 dB/m,而高阶模(HOMs)损耗为3.58 dB/m,有效模场面积可达2 313.67μm2。该光纤对弯曲方向不敏感,在高功率光纤激光器放大器等光通信器件领域具有广阔的发展前景。 相似文献
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The authors point out that random noise processes induce mode partition fluctuations in semiconductor lasers. Mode partition depends on laser parameters and modulation current. However, external optical feedback can also increase mode partition noise. Here, a numerical solution of multimode noise-driven rate equations with time-delayed terms is utilized to investigate mode partition in semiconductor lasers with reflecting feedback. Photon statistics of the main and side modes in semiconductor lasers under both CW operation and dynamic operation are considered. Probability-density curves for the main and side modes are shown. The feedback-induced change of photon statistics of the main and side modes is clearly seen. Numerical results indicate that, if the laser used is exposed to reflections, a more stringent mode discrimination requirement for suppressing the buildup of laser-cavity longitudinal side modes may result. If mode discrimination is insufficient for avoiding the excitation of side modes, the feedback-induced power penalty depends on the fiber dispersion 相似文献