DES算法的原理与实现

1、实验项目与实验报告（2 ）学科：信息与网络安全 学号:姓名：时间：月 日实验名称：DES算法的原理与实现 实验目的：1.熟悉DES算法的实现程序和具体应用，加深对DESM法的了解。实验内容：（写出实验内容要点或相关理论准备、实验估计）、DES1法的简介DES 算法为密码体制中的对称密码体制，又被称为美国数据加密标准，是1972年美国BM公司研制的对称密码体制加密算法。明文按64位进行分组，密钥长 64位，密钥事实上是 56位参与DES运算（第8、16、24、32、40、48、56、64位是校验位，使得每个密钥都有奇数个1）分组后的明文组和56位的密钥按位代替或交换的方法形成密文组的加密方法。

2、1、基本原理其入口参数有三个：key、data、mode Key为加密解密使用的密钥，data为加密解密的数据，mode为其工作模式。当模式为加密模式时，明文按照 64为进行分组，形成明文组， key用于对数据 加密，当模式为解密模式时，key用于对数据解密。实际运用中，密钥只用到了 64位中的56位，这样才具有高的安全性。密钥单轮运算位的扩展48位异或> 32位异或右半部分输出64位密文16轮运算图1 DES算法结构2、DES特点DES算法具有极高安全性，到目前为止，除了用穷举搜索法对DES算法进行攻击外，还没有发现更有效的办法。而 56位长的密钥的穷举空间为256 ,这意味着如果一台

3、计算机的速度是每一秒钟检测一百万个密钥，则它搜索完全部密钥就需要将近2285年的时间，可见，这是难以实现的。然而，这并不等于说 DES是不可破解的。而实际上，随着硬件技术和Intemet的发展，其破解的可能性越来越大，而且，所需要的时间越来越少。为了克服DES密钥空间小的缺陷，人们又提出了三重DES的变形方式。3、主要流程DES算法把64为的明文输入块变为 64位的密文输入块，它所使用的密钥也是 64位，整个算法 的主要流程图如下：(1 )置换规则表其功能是把输入的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：58,50,42,34,26,18,10,2

4、,60,52,44,36,28,20,12,4,62,54,46,38,30,22,14,6,64,56,48,40,32,24,16,8,57,49,41,33,25,17,9,1,59,51,43,35,27,19,11,3,61,53,45,37,29,21,13,5,63,55,47,39,31,23,15,7,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D1D2D3D64 ,则经过初始置换后的结果为：L0=D58D50D8 ; R0=D57D49D7

5、 。经过16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 正好是初始置换的逆运算。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位换回到第1位，其逆置换规则如下表所示：40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31,38,6,46,14,54,22,62,30,37,5,45,13,53,21,61,29,36,4,44,12,52,20,60,28,35,3,43,11,51,19,59,27,34,2,42,10,50,18,58 26,33,1,41,9,49,17,57,25,(

6、2)放大换位表32,1,2,3,4,5,4,5,6,7,8,9,8,9,10,11,12,13,12,13,14,15,16,17,16,17,18,19,20,21,20,21,22,23,24,25,24,25,26,27,28,29,28,29,30,31,32,1,(3)单纯换位表16,7,20,21,29,12,28,17,1,15,23,26,5,18,31,10,2,8,24,14,32,27,3,9,19,13,30,6,22,11,4,25,(4)功能表在f(Ri,Ki )算法描述图中，S1,S2.S8为选择函数，其功能是把 48bit数据变为32bit数据。下面 给出选择函

7、数Si(i=1,28 )的功能表：选择函数Si51:14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7,0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8,4,1,14,8,13,6,2,11,15,12,9,7,3,10,5,0, 15,12,8,2,4,9,1,7,5,11,3,14,10,0,6,13,52:15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10, 3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5, 0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15, 1

8、3,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9,53:10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8,13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1,13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7,1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12,54:7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15, 13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9, 10,6,9,0,12,11,7,13,15,1,3,

9、14,5,2,8,4, 3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14,55:2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9, 14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6,4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14,11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3,56:12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11,10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8,9,14,15,5,2,8,1

10、2,3,7,0,4,10,1,13,11,6,4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13,57:4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1,13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6,1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2,6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12,58:13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7,1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2,7,11,

11、4,1,9,12,14,2,0,6,10,13,15,3,5,8,2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11,在此以S1为例说明其功能，我们可以看到：在 S1中，共有4行数据，命名为0, 1、2、3行；每 行有16列，命名为0、1、2、3,14、15列。现设输入为：D=D1D2D3D4D5D6令：歹U =D2D3D4D5行=口1口6然后在S1表中查得对应的数，以4位二进制表示，此即为选择函数S1的输出。下面给出子密钥Ki (48bit)的生成算法。(5)子密钥的生成算法从子密钥Ki的生成算法描述图中我们可以看到： 初始Key值为64位，但DES算法规定，其中第

12、8、16、64位是奇偶校验位，不参与 DES运算。故Key实际可用位数便只有56位。即：经过缩 小选择换位表1的变换后，Key的位数由64位变成了 56位，此56位分为C0、D0两部分，各28位， 然后分别进行第1次循环左移，得到 C1、D1 ,将C1 (28位)、D1 (28位)合并得到56位，再经过缩 小选择换位2,从而便得到了密钥 K0 (48位)。依此类推，便可得到 K1、K2、K15 ,不过需要 注意的是，16次循环左移对应的左移位数要依据下述规则进行：(6)循环左移位数1,122,22221,2222221以上介绍了 DES算法的加密过程。DES算法的解密过程是一样的，区别仅仅在于

13、第一次替代时 用子密钥K15,第二次K14、，最后一次用 K0,算法本身并没有任何变化。二、源程序与代码实现1、源代码#include <stdio.h> #include <conio.h>/* initial permutation P*/；/* final permutation F */#define u8 unsigned char const static u8 ip64= 58, 50, 42, 34, 26, 18, 10, 2,60, 52, 44, 36, 28, 20, 12, 4,62, 54, 46, 38, 30, 22, 14, 6,64,

14、 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 const static u8 fp64= 40, 8, 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,

15、20, 60, 28,35, 3, 43, 11,51, 19, 59, 27,34, 2, 42, 10, 50, 18, 58, 26,33, 1,41, 9, 49, 17, 57, 25;/*unused*/const static u8 ei48 = 32, 1, 2, 3, 4, 5,4, 5, 6, 7, 8, 9,8, 9, 10, 11, 12, 13,12, 13, 14, 15, 16, 17,16, 17, 18, 19, 20, 21,20, 21,22, 23, 24, 25,24, 25, 26, 27, 28, 29,28, 29, 30, 31, 32, 1

16、;const static u8 pc156= 57, 49, 41, 33, 25, 17, 9,1, 58, 50, 42, 34, 26, 18,10, 2, 59, 51,43, 35, 27,19, 11, 3, 60, 52, 44, 36,63, 55, 47, 39, 31,23, 15,7, 62, 54, 46, 38, 30, 22,14, 6, 61,53, 45, 37, 29,21, 13, 5, 28, 20, 12, 4;const static u8 totrot16*/=1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1expansion ope

17、ration matrix */*/* permuted choice table (key) */*number left rotations；rwo:of pc1const static u8 pc248= 14, 17, 11,24, 1, 5,3, 28, 15, 6, 21, 10,23, 19, 12, 4, 26, 8,16, 7, 27, 20, 13, 2,41,52, 31,37, 47, 55,30, 40, 51,45, 33, 48,44, 49, 39, 56, 34, 53,46, 42, 50, 36, 29, 32;/* permuted choice key

18、 (table) */const static u8 si864/* 48->32 bit compression tables*/=/* S1 */14, 4, 13, 1, 2,15,11, 8, 3,10, 6,12, 5, 9, 0, 7,0,15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8,4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0,15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13,/* S2 */15, 1,

19、8,14,6,11,3, 4,9,7,2, 13, 12,0,5, 10,16, 13, 4,7,15,2,8, 14,12,0,1, 10,6,9,11, 5,2, 14, 7,11,10,4,13, 1, 5,8,12, 6,9,3,2, 15,13, 8, 10, 1,3,15,4, 2,11,6,7, 12,0,5,14, 9,/* S3 */14, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8,15, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1,16, 6, 4, 9,8,15,

20、3,0,11,1,2,12, 5,10,14, 7,1, 10, 13, 0,6,9,8,7,4, 15,14,3, 11, 5,2, 12,/* S4 */7, 13, 14, 3,0,6,9,10,1,2,8,5, 11,12,4, 15,13, 8, 11, 5,6,15,0, 3,4,7,2,12, 1,10,14, 9,10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4,3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14,/* S5 */2, 12, 4, 1, 7, 10,

21、11,6, 8,5,3, 15, 13, 0,14,9,14, 11, 2, 12, 4, 7, 13,1, 5,0,15,10, 3, 9,8,6,4, 2, 1, 11, 10, 13, 7,8, 15,9,12,5, 6, 3,0, 14,11, 8, 12, 7, 1, 14, 2,13, 6,15,0,9, 10, 4,5,3,/* S6 */12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11,10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8,9, 14, 15, 5, 2,

22、 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6,4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13,/* S7 */4, 11, 2, 14, 15,0,8, 13, 3, 12, 9, 7, 5, 10,6,1,13, 0, 11, 7, 4,9,1, 10, 14, 3, 5, 12, 2, 15,8,6,1, 4, 11, 13, 12,3,7, 14, 10, 15, 6, 8, 0, 5,9,2,6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12,/*

23、 S8 */13, 2, 8,4,6,15,11,1,10,9,3,14,5,0,12,7,1, 15, 13, 8,10, 3,7,4,12,5,6,11,0,14,9,2,7, 11, 4,1,9,12,14,2,0,6, 10,13,15, 3,5,8,2, 1, 14,7,4,10,8, 13,15,12,9,0,3,5,6, 11;const static u8 p32i32/* 32-bit permutation function */=16, 7, 20, 21,29, 12, 28, 17,1, 15, 23, 26,5, 18, 31, 10,2, 8, 24, 14,32

24、, 27, 3, 9,19, 13, 30, 6,22, 11, 4, 25;const static u8 bitmap8 = 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01;void main()u8 Key8, Input8, Output8;/* Key8,Input8, Output8 ;*/u8 Subkey1648;u8 Data_Left32, Data_Right32;int k;void Generate_Subkey( u8 Key8, u8 Subkey1648);void DES_E(u8 Input8, u8 Outpu

25、t8, u8 Data_Left32, u8 Data_Right32, u8 Subkey16 48);void DES_D(u8 Input8, u8 Output8, u8 Data_Left32, u8 Data_Right32, u8 Subkey16 48);printf("nPlease input a key of 8 letters:n");fflush(stdin);for (k=0;k<8;k+)scanf("%c”,&Keyk);printf("nPlease input a plaintext of 8 lette

26、rs:n");fflush(stdin);for(k=0;k<8;k+)scanf("%c",&Inputk);Generate_Subkey(Key, Subkey);DES_E(Input, Output, Data_Left, Data_Right, Subkey);printf("nthe Plaintext is :n");for(k=0;k<8;k+)printf("%c",Inputk);printf("nthe cipher in hex is :n");for(k=0

27、;k<8;k+)printf("%#x ",Outputk);DES_D(Output, Input, Data_Right, Data_Left, Subkey);printf("nnthe cipher in char is :n");for(k=0;k<8;k+)printf("%c",Outputk);printf("nthe Plaintext is :n");for(k=0;k<8;k+)printf("%c",Inputk);void Generate_Subke

28、y( u8 Key8, u8 Subkey1648)u8 temp64;u8 temp156;u8 Ci28;u8 Di28;u8 bittemp;int n, i, j ;for ( i=0; i<8; i+ )printf("%#x'n",Keyi);for ( j=0; j<8; j+ )if (Keyi & bitmap8-j) tempi*8+j = 1 ;else tempi*8+j = 0 ; /*set 1 or 0 to temp64 */printf("%d",tempi*8+j); printf(&quo

29、t;n");for ( i=0 ; i<56 ; i+)temp1i=temppc1i-1;for ( i=0; i<28; i+ ) Cii = temp1 i ;Dii = temp1 28+i ;for (n=0;n<16;n+)for (i=0;i<totrotn;i+)bittemp = Ci0;for ( j = 0； j <27; j+)Cij = Cij+1；Ci27 = bittemp;bittemp = Di0;for (j = 0; j <27; j+)Dij = Dij+1;Di27 = bittemp;for (i=0;i

30、<28;i+) temp1i = Cii;temp127+i = Dii;for (i=0;i<48;i+)Subkeyni = temp1 pc2i - 1 ; void Initial_Permutation( u8 Input8, u8 Data_Left32, u8 Data_Right 32)u8 temp64;int i, j ;for ( i=0; i<8; i+ )for(j=0; j<8; j+ )if (Inputi & bitmap7-j ) tempi*8+j = 1 ;else tempi*8+j = 0 ;for ( i=0; i&l

31、t;32; i+ )Data_Lefti = temp ipi - 1 ;Data_Righti = temp ip32+i - 1 ;void Inverse_Initial_Permutation(u8 Data_Left32, u8 Data_Right32, u8 Output8) u8 temp64 , temp264; int i, j ;for( i=0; i<32; i+ )temp i = Data_Lefti;tempi+32 = Data_Righti;for ( i=0; i<64; i+ )temp2i = temp fpi - 1 ;for ( i=0;

32、 i<8; i+ ) Outputi = 0 ;for ( i=0; i<8; i+ )for ( j=0; j<8; j+ )if ( temp2i*8+j) Output i |= bitmap7-j;void E_Permutation( u8 Right32, u8 temp48)int i ;for ( i=0; i<48; i+ )temp i = Right ei i - 1 ;void P_Permutation( u8 temp32, u8 f32)int i;for ( i=0; i<32; i+ )fi = temp p32ii - 1 ;v

33、oid S_Box( u8 temp48, int n )/*0<=n<8*/u8 In6, Out4;int i, j ；u8 s;for( i=0; i<6; i+ )Ini = temp n*6+i ;i = 0 ;if ( In5 ) i = 1 ;if (In0 ) i+= 2 ;if ( In4 ) j = 1 ;if ( In3 ) j+= 2 ;if ( In2 ) j+= 4 ;if ( In1 ) j+= 8 ；s = si n i*16+j ;for( i=0; i<4; i+ )if (s & bitmap7-i) temp n*4 +

34、i = 1;else temp n*4 + i = 0;void F_function( u8 Right32, u8 Subkey1648, int No, u8 f32)u8 temp48;int i ;for( i=0; i<48; i+ )tempi = 0 ;E_Permutation( Right, temp );for( i=0; i<48; i+ )tempi A= Subkey No i ;for( i=0; i<8; i+ )S_Box( temp, i );P_Permutation( temp, f );void Encript_Loop( u8 Data_Left32, u8 Data_Right32, u8 Subkey1648, int No ) u8 Temp32, temp232;int i, j；for( i=0; i<32; i+ )Temp i = Data_Left i ;Data_Left i = Data_Right i ;F_function( Data_Right, Subkey, No, temp2 );for( i=0; i<32; i+ ) D