| 建栋 的个人资料KEN's Space照片日志列表 |  工具  帮助 |
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12月2日 DES算法
.....当DES算法被建议作为一个标准时，曾出现过很多批评，其中最有争议的问题之一就是S盒。S盒是DES算法的核心，因为在DES算法中，除了S盒外，所有计算都是线性的。然而S盒的设计准则并没有完全得到规范。有人认为S盒可能存在陷门。不能排除这种说法，但至今没有迹象表明S盒中存在陷门。 1976年，美国国家安全局公布了下列几条S盒的设计原则： 1.S盒的每一行是整数0，1，...，15的一个置换； 2.没有一个S盒是它输入的线性或仿射函数； 3.改变S盒的一个输入比特至少要引起两比特的输出改变； 4. ....... 5. ....... 6. ....... 12月1日 Sand Writinga story tells of two friends who were walking through the desert.at a specific point of the journey,they had an argument,and one friend slapped the other one in the face.the one,
who got slapped,was hurt,but without anything to say,he wrote in the sand,"Today my best friend slapped me in the face."
they kept on walking,until they found an oasis,where they decided to take a bath.the one who got slapped and hurt started drowning,and the other friend saved him.when he recovered from the fright,he wrote on a stone,"Today my best friend saved my life."
the friend who saved and slapped his best friend,asked him,"Why,after I hurt you,you wrote in the sand,and now you write on a stone?"the other friend,smiling,replied,"When a friend hurts us,we should write it down in the sand,where the winds of forgiveness can erase it away,and when something happens,we should engrave it in the stone of the memory of the heart,where no wind can erase it."
Let's learn to write in the sand more. |
真烦阿……|
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