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71.
抗几何攻击图像水印方案 总被引:1,自引:0,他引:1
几何形变一直是各类数字水印算法较难抵抗的攻击手段。针对此问题,提出一种抗几何攻击数字图像水印算法。采用周期性的水印嵌入图像,强度由NVF函数确定。在检测时,用白化滤波器对图像进行预处理。由于水印数据是随机的,而图像数据高度相关,白化滤波器起到增加水印数据能量,同时降低图像数据能量的作用。由理论计算得出选择滤波器的原则。然后,通过自相关检测,得到反映几何形变的峰值点。对实验结果的分析证明,该算法对各类几何攻击都能够精确定位。 相似文献
72.
从海上作战对电子对抗作战能力的需求出发,分析了电子情报能力、电子防御能力、电子进攻能力和电子防护能力在现代海战中的需求,提出了未来电子对抗装备的网络化、一体化和无人化的发展趋势。 相似文献
73.
Jason Lin 《Optics Communications》2011,284(9):2412-2414
Recently, Chen et al. presented a novel quantum private comparison (QPC) protocol using triplet GHZ state to enable two parties to compare the equality of their information without revealing the content. The protocol is rather promising because it only requires single-photon measurement with the help of a semi-honest third party to complete the secret comparison. However, this study will point out that a weakness could occur in the eavesdropping check phase. That is, an intercept-resend attack could be launched by one of the two participants to reveal the information content of the other participant—a result that contradicts to the security requirement of a QPC. Fortunately, two solutions are possible to avoid the attack. 相似文献
74.
介绍了卫星制导武器直接瞄准攻击方式在对地精确打击中占据的关键位置,阐述了卫星制导武器直接瞄准攻击方法的原理。由于卫星制导武器直接瞄准攻击对目标定位要求较高,采用常用定位手段已不能满足系统对目标定位的要求,分析了使用相对GPS制导成为卫星制导武器直接瞄准攻击的关键的原因。相对GPS制导误差主要包括采用载机和武器相对GPS定位误差以及传感器对目标的相对定位误差,分别对两者的定位精度进行了分析和推导。仿真结果表明:这两者的综合误差理论值小于7.5 m,满足卫星制导武器在直接瞄准攻击中对目标定位的需求。 相似文献
75.
Optimal quantitative cryptanalysis of permutation-only multimedia ciphers against plaintext attacks 总被引:1,自引:0,他引:1
Recently, an image scrambling encryption algorithm of pixel bit based on chaos map was proposed. Considering the algorithm as a typical binary image scrambling/permutation algorithm exerting on plaintext of size M×(8N), this paper proposes a novel optimal method to break it with some known/chosen-plaintexts. The spatial complexity and computational complexity of the attack are only O(32·MN) and O(16·n0·MN) respectively, where n0 is the number of known/chosen-plaintexts used. The method can be easily extended to break any permutation-only encryption scheme exerting on plaintext of size M×N and with L different levels of values. The corresponding spatial complexity and computational complexity are only O(MN) and O(⌈logL(MN)⌉·MN) respectively. In addition, some specific remarks on the performance of the image scrambling encryption algorithm are presented. 相似文献
76.
Parallel Collision Search with Cryptanalytic Applications 总被引:16,自引:0,他引:16
A simple new technique of parallelizing methods for solving search problems which seek collisions in pseudorandom walks is
presented. This technique can be adapted to a wide range of cryptanalytic problems which can be reduced to finding collisions.
General constructions are given showing how to adapt the technique to finding discrete logarithms in cyclic groups, finding
meaningful collisions in hash functions, and performing meet-in-the-middle attacks such as a known-plaintext attack on double
encryption. The new technique greatly extends the reach of practical attacks, providing the most cost-effective means known
to date for defeating: the small subgroup used in certain schemes based on discrete logarithms such as Schnorr, DSA, and elliptic
curve cryptosystems; hash functions such as MD5, RIPEMD, SHA-1, MDC-2, and MDC-4; and double encryption and three-key triple
encryption. The practical significance of the technique is illustrated by giving the design for three $10 million custom machines
which could be built with current technology: one finds elliptic curve logarithms in GF(2155) thereby defeating a proposed elliptic curve cryptosystem in expected time 32 days, the second finds MD5 collisions in expected
time 21 days, and the last recovers a double-DES key from two known plaintexts in expected time 4 years, which is four orders
of magnitude faster than the conventional meet-in-the-middle attack on double-DES. Based on this attack, double-DES offers
only 17 more bits of security than single-DES.
Received 21 December 1995 and revised 24 September 1996 相似文献
77.
78.
Substituted carbonylmanganese cations [Mn(CO)5L]+, where L=py, PPh3 and PPh2Me, readily react with various organoborate anions (tetramethylborate, methyltriphenylborate and tetraphenylborate) in THF solution to afford a mixture of dimanganese carbonyls, hydridomanganese carbonyls and alkylmanganese carbonyls. The formation of the dimanganese carbonyl dimers as well as the hydridomanganese carbonyls suggests the involvement of 19-electron carbonylmanganese radicals that stem from an initial electron transfer. On the other hand, the acetonitrile-substituted analogue [Mn(CO)5(CH3CN)]+ reacts with the same borate anions to afford the alkylated RMn(CO)5, where R=CH3 and C6H5, as the sole carbonylmanganese product. As such, this alkylative annihilation is best formulated as a direct attack on the carbonyl carbon by the borate nucleophile. The two different pathways can be understood in terms of the balance between the electrophilicity of the carbonyl ligand and the electron affinity of the carbonylmanganese cation. 相似文献
79.
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