【摘要】：哈希函數(shù)在密碼學(xué)安全領(lǐng)域及網(wǎng)絡(luò)應(yīng)用等方面扮演著極為重要的角色,其在數(shù)字簽名、密碼保存等許多領(lǐng)域都有著比較廣泛的應(yīng)用。但是隨著密碼分析者已經(jīng)能在較短的時(shí)間內(nèi)有效地找到MD5、SHA0、SHA1等的碰撞,則表明傳統(tǒng)的哈希函數(shù)已經(jīng)遭受了很嚴(yán)重的安全問題。因此,近些年針對(duì)哈希函數(shù)出現(xiàn)的各種安全和效率問題,研究者們主要從兩個(gè)方面提出了不同的函數(shù)設(shè)計(jì)方案,一個(gè)是針對(duì)迭代結(jié)構(gòu)的改進(jìn),另一個(gè)則是針對(duì)壓縮函數(shù)的改進(jìn)。前者重在提高函數(shù)的運(yùn)行效率,后者旨在提高函數(shù)的安全性。并行結(jié)構(gòu)具有很高的運(yùn)行效率引起了越來越多的研究者的注意,混沌映射對(duì)系統(tǒng)參數(shù)具有很高靈敏性,成為設(shè)計(jì)哈希函數(shù)的一種新的思路。本文針對(duì)哈希函數(shù)運(yùn)行效率不高、不具備可證明抗碰撞性等特點(diǎn),引入了并行結(jié)構(gòu)、混沌映射、基于格上的轉(zhuǎn)換等設(shè)計(jì)方法,對(duì)哈希函數(shù)的迭代結(jié)構(gòu)和壓縮函數(shù)分別進(jìn)行了改進(jìn)。本文主要工作內(nèi)容安排如下:1)針對(duì)SHA256運(yùn)行效率不高的問題,本文設(shè)計(jì)了基于并行結(jié)構(gòu)的SHA256改進(jìn)算法。原來算法的消息計(jì)算是采用串行計(jì)算的方式,需要把上一個(gè)消息分組計(jì)算得出的值作為下一個(gè)消息塊的輸入值,因此若要計(jì)算出后一個(gè)消息分組的值只有先計(jì)算出上一個(gè)消息分組的值。當(dāng)參與運(yùn)算的消息足夠大時(shí),則會(huì)造成計(jì)算效率很低。對(duì)于出現(xiàn)的這一問題,我們?cè)O(shè)計(jì)了并行結(jié)構(gòu)的哈希算法。當(dāng)消息進(jìn)行分組之后,先計(jì)算出各個(gè)消息塊的值,然后在接下來的一輪計(jì)算中再把每?jī)蓚�(gè)消息塊進(jìn)行結(jié)合運(yùn)算。當(dāng)該輪計(jì)算中消息塊的個(gè)數(shù)是奇數(shù)時(shí),再添加一個(gè)消息塊的值,因此經(jīng)過一輪運(yùn)算消息塊的個(gè)數(shù)將會(huì)減少近一半。依次進(jìn)行類似的運(yùn)算,直到最終剩余一個(gè)消息塊的值,將該值作為最終的哈希值。在奇數(shù)輪和偶數(shù)輪的運(yùn)算中,消息塊分組采用了不同的結(jié)合方式進(jìn)行計(jì)算。最后通過理論分析和實(shí)驗(yàn)仿真對(duì)所提的方案進(jìn)行了分析,表明所提方案是可行的和先進(jìn)的。2)SHA1在運(yùn)行效率上明顯優(yōu)于SHA256,但是其卻面臨著重要的安全問題,目前已經(jīng)找到了SHA1的部分碰撞。本文主要對(duì)SHA1的壓縮函數(shù)進(jìn)行了改進(jìn),在設(shè)計(jì)壓縮函數(shù)的過程中引入了混沌映射,利用多混沌映射之間的切換,將混沌映射與壓縮函數(shù)相結(jié)合,通過多次混合迭代來控制其中間鏈接變量值,以增強(qiáng)函數(shù)的雪崩性。在對(duì)最后一個(gè)消息塊進(jìn)行處理時(shí)引入了格的思想,設(shè)計(jì)了基于格上的可證明抗碰撞性的哈希函數(shù)。將經(jīng)過格變換之后的值作為最終輸出的哈希值,在安全性證明中將哈希函數(shù)的抗碰撞性規(guī)約到格上難題并證明該問題的困難性。最后對(duì)所提的方案進(jìn)行了理論分析和實(shí)驗(yàn)仿真。
[Abstract]:Hash function plays an important role in cryptography security and network applications. It has been widely used in many fields such as digital signature, cryptographic preservation and so on. However, since the cryptographer has been able to find the collision of MD5,SHA0,SHA1 and so on effectively in a short time, it shows that the traditional hash function has suffered a serious security problem. Therefore, in recent years, for various security and efficiency problems of hash functions, researchers have mainly proposed two different function design schemes, one is for the improvement of iterative structure, the other is for the improvement of compression function. The former focuses on improving the efficiency of the function, while the latter aims to improve the security of the function. The high efficiency of parallel structure has attracted more and more researchers' attention. Chaotic mapping is highly sensitive to system parameters and has become a new way to design hash functions. In this paper, we introduce parallel structure, chaotic mapping, transformation based on lattice and other design methods, aiming at the features that hash function is not efficient and can be proved to resist collision. The iterative structure and the compression function of the hash function are improved respectively. The main work of this paper is as follows: 1) aiming at the low efficiency of SHA256, an improved SHA256 algorithm based on parallel architecture is designed in this paper. The original algorithm of message calculation is a serial calculation method, it is necessary to take the value calculated from the previous message packet as the input value of the next message block. Therefore, to calculate the value of the latter message packet, only the value of the previous message packet is calculated. When the message involved in the operation is large enough, the computation efficiency is very low. For this problem, we design a parallel hash algorithm. When the messages are grouped, the values of each message block are calculated first, and then each two message blocks are combined in the next round of calculations. When the number of message blocks in this round is odd, the value of a message block is added, so the number of message blocks will be reduced by nearly half after a round operation. A similar operation is performed until the final value of a message block is used as the final hash value. In the operations of odd and even rounds, message block grouping is calculated in different combinations. Finally, through theoretical analysis and experimental simulation, the proposed scheme is analyzed, which shows that the proposed scheme is feasible and advanced. 2) SHA1 is obviously superior to SHA256, in operation efficiency, but it is faced with important security problems. A partial collision of SHA1 has been found. In this paper, the compression function of SHA1 is improved. Chaotic mapping is introduced in the process of designing the compression function. The chaotic mapping is combined with the compression function by switching between multiple chaotic maps. In order to enhance the avalanche of the function, the interlinked variable value is controlled by multiple mixed iterations. The idea of lattice is introduced when the last message block is processed, and a hashing function based on lattice is designed to prove collision resistance. The value after lattice transformation is taken as the final output hash value. In the security proof, the collision resistance of the hash function is reduced to the problem on the lattice and the difficulty of the problem is proved. Finally, the theoretical analysis and experimental simulation of the proposed scheme are carried out.
【學(xué)位授予單位】：深圳大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TN918.1

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