文档介绍：哈尔滨理工大学课程设计题目:DES算法院、系:计算机科学与技术学院网络工程系班级: 网络学号:姓名:同组成员:指导教师:成绩:2014年06月27日系统设计的目标理解对称加解密算法的原理和特点;理解DES算法的加解密原理;二•系统原理:(―) 加密DES算法把64位的明文输入块变为64位的密文输出块,它所使用的密钥也是64位,其功能是把输入的64位数据块按位重新组合,并把输出分为L0、R0两部分,每部分各长32位,其置换规则见下表:5&50,12,34,26,1&10,2,60,52,44,36,2&20,12,4,62,54,46,38,30,22,14,6,64,56,48,40,32,24,16,8,57,49,41,33,25,17,9,1,59,51,43,35,27,19,11,3,61,53,45,37,29,21,13,5,63,55,47,39,31,23,15,7,即将输入的第58位换到第一位,第50位换到第2位,……,依此类推,最后一位是原来的第7位。L0、R0则是换位输出后的两部分,L0是输出的左32位,R0是右32位,例:设置换前的输入值为D1D2D3……D64,则经过初始置换后的结果为:L0二D550……D8;R0二D57D49…D7。经过26次迭代运算后,得到L16、R16,将此作为输入,进行逆置换,即得到密文输出。逆置换正好是初始置的逆运算,例如,第1位经过初始置换后,处于第40位,而通过逆置换,又将第40位换冋到第1位,其逆置换规则如下表所示:40,& 48,16,56, 24, 64,32, 39, 7, 47, 15, 55, 23,63,31,38,6, 46,14,54, 22, 62,30, 37, 5, 45, 13, 53, 21,61,29,36,4, 44,12,52, 20, 60,28, 35, 3, 43, 11, 51, 19,59,27,34,2, 42,10,50, 18, 5826, 33, 1, 41, 9,49,17,57,25,放大换位表32,1,2,3,4,5,4, 5,6,7,8,9,8, 9,10,11,13,12,13,14, 15,16,17,16, 17,18,19, 20, 21,20, 21,22,23,24,25,24, 25,26,27,2& 29,2&29, 30, 31,32, 1,单纯换位表16,7,20,21,29,12,28,17,1,15,23,26,5,18,31,10,8,24,14,32,27,3,9,19,13,30,6,22,11,4,25,在f(Ri,Ki)算法描述图中,S1,S2.・・S8为选择函数,其功能是把6bit数据变为4bit数据。下面给出选择函数Si(i二1,2 8)的功能表:选择函数SiSI:4,13,1,2,15,11,&3,10,6,12,5,S0,15,7,4,14,2,13,1,10,6,12,11,9,54,1,14,8,13,6,2,11,15,12,9,7,3,1C12,8,2,4,9,1,7,5,11,3,14,10,0,S2:15,1,8,14,6,11,3,4,9,7,2,13,12,0,13,4,7,15,2,8,14,12,0,1,10,6,9,0,14,7,11,10,4,13,1,5,8,12,6,9,3,&10,1,3,15,4,2,11,6,7,12,0,5,S3:0,9,14,6,3,15,5,1,13,12,7,11,413,7,0,9,3,4,6,10,2,&5,14,12,11,13,6,4,9,8,15,3,0,11,1,2,12,5,10,10,13,0,6,9,8,7,4,15,14,3,11,5,S4:7,13,14,3,0,6,9,10,1,2,8,5,11,12,8,11,5,6,15,0,3,4,7,2,12,1,10,6,9,0,12,11,7,13,15,1,3,14,5,215,0,6,10,1,13,&9,4,5,11,12,7,S5:12,4,1,7,10,11,6,8,5,3,15,13,0,11,2,12,4,7,13,1,5,0,15,10,3,S4,2,1,11,10,13,7,8,15,9,12,5,6,3,&12,7,1,14,2,13,6,15,0,9,10,4S6:1,10,15,9,2,6,&0,13,3,4,14,7,10,15,4,2,7,12,9,5,6,1,13,14,0,119,14,15,5,2,8,12,3,7,0,4,10,1,13,3,2,12,9,5,15,10,11,14,1,7,6,0,S7:4,11,2,14,15,0,8,13,3,12,9,7,5,1C0,11,7,4,9,1,10,14,