杂凑函数原象攻击方法研究.pdf

西安电子科技大学硕士学位论文杂凑函数原象攻击的方法研究姓名:阎娜申请学位级别:硕士专业:密码学指导教师:李梦东 20100101 摘要摘要 Hash函数作为密码学的一个重要工具,在数字签名、消息认证和数据完整性方面有着广泛的应用。关于Hash函数的安全性分析是密码学中的一个重要而活跃的研究课题。近来出现的常见Hash函数算法的原象攻击方法,对于Hash函数的研究具有重要意义。与碰撞攻击相比较,原象攻击的难度较大,但原象攻击对 Hash函数的影响将是致命的。、,提出了改进方案,主要完成的工作如下: (1)、压缩函数的可逆性、消息扩展方式的特殊性、中间相遇攻击以及随机图理论进行了深入的研究和总结。(2),分别提出两种改进方案。第一种方案将攻击的空间复杂度从231降低到216,第二种方案将攻击的时间复杂度从2102降低到298。(3)深入分析了Yu ,进一步探讨了Leurent 。,。同时对一种新的可行初始结构方式进行了探讨。(4) 步SHA-0原象攻击方法,并尝试用消息修改技术解决状态变量的选取问题;同时对部分伪原象的计算与转化的复杂度的平衡点问题进行了探索。关键词:Hash函数原象攻击随机图初始结构 Abstract Abst ract As an important toolincryptography,hash functions have been widely used in digital signatures,message authentication,data integrity and SO security analysis of hash functions is adominant and active topic appeared preimage attacks on hash function algorithms play avery important rolein pared with thecollisionattack,the preimage attackis more difficult to ,the preimage attackhas afataleffect on hashfunctions. Inthisthesis,the methods ofpreimage attacks on MD一4,MD一5 and SHA一0 which were proposed on the international conference forthe past two years are theimproved schemes main work inthisthesis includes: (1)The absorption properties ofboolean functions,reversibility pression functions,specificity ofmessage expansion on MD一4,the meet-in—middle attacks and random graph theory are researched andsummarized deeply. (2)Leurent’S method isimproved by our plexity ofthe attackisreduced from 231 to216by plexity oftheattack isreduced from 2102 to298by thesecond scheme。(3)The difficulties that the Leurent’S method applies toMD一5 are further ofpreimage attacksbetween ones tothereduced steps ,the idea ofYu