DES算法详述

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，整个算法的主流程图如下：
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：
58,50,12,34,26,18,10,2,60,52,44,36,28,20,12,4,
　　 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D1D2D3……D64，则经过初始置换后的结果为：L0=D58D50…D8；R0=D57D49…D7。
　　 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,
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,
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,
　　 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=1,2……8)的功能表：
选择函数Si
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:
　　 15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10,
　　 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,
　　 13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9,
S3:
　　 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,
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:
　　 2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9,
　　 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,
　　 9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6,
　　 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,
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,
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：列＝D2D3D4D5
　　 行＝D1D6
　　 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
　　 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：
循环左移位数
1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1
　　 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，区别仅仅在于第一次迭代时用子密钥K15，第二次K14、……，最后一次用K0，算法本身并没有任何变化。


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/* ============================================================ ====
des()
Description: DES algorithm,do encript or descript.
============================================================ ==== */
int des(unsigned char *source,unsigned char * dest,unsigned char * inkey, int flg)
{
unsigned char bufout[64],
kwork[56], worka[48], kn[48], buffer[64], key[64],
nbrofshift, temp1, temp2;
int valindex;
register i, j, k, iter;

/* INITIALIZE THE TABLES */
/* Table – s1 */
static unsigned char s1[4][16] = {
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 };

/* Table – s2 */
static unsigned char s2[4][16] = {
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,
13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9 };

/* Table – s3 */
static unsigned char s3[4][16] = {
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 };

/* Table – s4 */
static unsigned char s4[4][16] = {
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 };

/* Table – s5 */
static unsigned char s5[4][16] = {
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 };

/* Table – s6 */
static unsigned char s6[4][16] = {
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, 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 };

/* Table – s7 */
static unsigned char s7[4][16] = {
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 };

/* Table – s8 */
static unsigned char s8[4][16] = {
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 };


/* Table – Shift */
static unsigned char shift[16] = {
1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1 };


/* Table – Binary */
static unsigned char binary[64] = {
0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1,
0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 1, 1, 1,
1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 1,
1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 0, 1, 1, 1, 1 };

/* MAIN PROCESS */
/* Convert from 64-bit key into 64-byte key */
for (i = 0; i < 8; i++) {
key[8*i] = ((j = *(inkey + i)) / 128) % 2;
key[8*i+1] = (j / 64) % 2;
key[8*i+2] = (j / 32) % 2;
key[8*i+3] = (j / 16) % 2;
key[8*i+4] = (j / % 2;
key[8*i+5] = (j / 4) % 2;
key[8*i+6] = (j / 2) % 2;
key[8*i+7] = j % 2;
}

/* Convert from 64-bit data into 64-byte data */
for (i = 0; i < 8; i++) {
buffer[8*i] = ((j = *(source + i)) / 128) % 2;
buffer[8*i+1] = (j / 64) % 2;
buffer[8*i+2] = (j / 32) % 2;
buffer[8*i+3] = (j / 16) % 2;
buffer[8*i+4] = (j / % 2;
buffer[8*i+5] = (j / 4) % 2;
buffer[8*i+6] = (j / 2) % 2;
buffer[8*i+7] = j % 2;
}

/* Initial Permutation of Data */
bufout[ 0] = buffer[57];
bufout[ 1] = buffer[49];
bufout[ 2] = buffer[41];
bufout[ 3] = buffer[33];
bufout[ 4] = buffer[25];
bufout[ 5] = buffer[17];
bufout[ 6] = buffer[ 9];
bufout[ 7] = buffer[ 1];
bufout[ 8] = buffer[59];
bufout[ 9] = buffer[51];
bufout[10] = buffer[43];
bufout[11] = buffer[35];
bufout[12] = buffer[27];
bufout[13] = buffer[19];
bufout[14] = buffer[11];
bufout[15] = buffer[ 3];
bufout[16] = buffer[61];
bufout[17] = buffer[53];
bufout[18] = buffer[45];
bufout[19] = buffer[37];
bufout[20] = buffer[29];
bufout[21] = buffer[21];
bufout[22] = buffer[13];
bufout[23] = buffer[ 5];
bufout[24] = buffer[63];
bufout[25] = buffer[55];
bufout[26] = buffer[47];
bufout[27] = buffer[39];
bufout[28] = buffer[31];
bufout[29] = buffer[23];
bufout[30] = buffer[15];
bufout[31] = buffer[ 7];
bufout[32] = buffer[56];
bufout[33] = buffer[48];
bufout[34] = buffer[40];
bufout[35] = buffer[32];
bufout[36] = buffer[24];
bufout[37] = buffer[16];
bufout[38] = buffer[ 8];
bufout[39] = buffer[ 0];
bufout[40] = buffer[58];
bufout[41] = buffer[50];
bufout[42] = buffer[42];
bufout[43] = buffer[34];
bufout[44] = buffer[26];
bufout[45] = buffer[18];
bufout[46] = buffer[10];
bufout[47] = buffer[ 2];
bufout[48] = buffer[60];
bufout[49] = buffer[52];
bufout[50] = buffer[44];
bufout[51] = buffer[36];
bufout[52] = buffer[28];
bufout[53] = buffer[20];
bufout[54] = buffer[12];
bufout[55] = buffer[ 4];
bufout[56] = buffer[62];
bufout[57] = buffer[54];
bufout[58] = buffer[46];
bufout[59] = buffer[38];
bufout[60] = buffer[30];
bufout[61] = buffer[22];
bufout[62] = buffer[14];
bufout[63] = buffer[ 6];

/* Initial Permutation of Key */
kwork[ 0] = key[56];
kwork[ 1] = key[48];
kwork[ 2] = key[40];
kwork[ 3] = key[32];
kwork[ 4] = key[24];
kwork[ 5] = key[16];
kwork[ 6] = key[ 8];
kwork[ 7] = key[ 0];
kwork[ 8] = key[57];
kwork[ 9] = key[49];
kwork[10] = key[41];
kwork[11] = key[33];
kwork[12] = key[25];
kwork[13] = key[17];
kwork[14] = key[ 9];
kwork[15] = key[ 1];
kwork[16] = key[58];
kwork[17] = key[50];
kwork[18] = key[42];
kwork[19] = key[34];
kwork[20] = key[26];
kwork[21] = key[18];
kwork[22] = key[10];
kwork[23] = key[ 2];
kwork[24] = key[59];
kwork[25] = key[51];
kwork[26] = key[43];
kwork[27] = key[35];
kwork[28] = key[62];
kwork[29] = key[54];
kwork[30] = key[46];
kwork[31] = key[38];
kwork[32] = key[30];
kwork[33] = key[22];
kwork[34] = key[14];
kwork[35] = key[ 6];
kwork[36] = key[61];
kwork[37] = key[53];
kwork[38] = key[45];
kwork[39] = key[37];
kwork[40] = key[29];
kwork[41] = key[21];
kwork[42] = key[13];
kwork[43] = key[ 5];
kwork[44] = key[60];
kwork[45] = key[52];
kwork[46] = key[44];
kwork[47] = key[36];
kwork[48] = key[28];
kwork[49] = key[20];
kwork[50] = key[12];
kwork[51] = key[ 4];
kwork[52] = key[27];
kwork[53] = key[19];
kwork[54] = key[11];
kwork[55] = key[ 3];

/* 16 Iterations */
for (iter = 1; iter < 17; iter++) {
for (i = 0; i < 32; i++)
buffer = bufout[32+i];

/* Calculation of F(R, K) */
/* Permute – E */
worka[ 0] = buffer[31];
worka[ 1] = buffer[ 0];
worka[ 2] = buffer[ 1];
worka[ 3] = buffer[ 2];
worka[ 4] = buffer[ 3];
worka[ 5] = buffer[ 4];
worka[ 6] = buffer[ 3];
worka[ 7] = buffer[ 4];
worka[ 8] = buffer[ 5];
worka[ 9] = buffer[ 6];
worka[10] = buffer[ 7];
worka[11] = buffer[ 8];
worka[12] = buffer[ 7];
worka[13] = buffer[ 8];
worka[14] = buffer[ 9];
worka[15] = buffer[10];
worka[16] = buffer[11];
worka[17] = buffer[12];
worka[18] = buffer[11];
worka[19] = buffer[12];
worka[20] = buffer[13];
worka[21] = buffer[14];
worka[22] = buffer[15];
worka[23] = buffer[16];
worka[24] = buffer[15];
worka[25] = buffer[16];
worka[26] = buffer[17];
worka[27] = buffer[18];
worka[28] = buffer[19];
worka[29] = buffer[20];
worka[30] = buffer[19];
worka[31] = buffer[20];
worka[32] = buffer[21];
worka[33] = buffer[22];
worka[34] = buffer[23];
worka[35] = buffer[24];
worka[36] = buffer[23];
worka[37] = buffer[24];
worka[38] = buffer[25];
worka[39] = buffer[26];
worka[40] = buffer[27];
worka[41] = buffer[28];
worka[42] = buffer[27];
worka[43] = buffer[28];
worka[44] = buffer[29];
worka[45] = buffer[30];
worka[46] = buffer[31];
worka[47] = buffer[ 0];

/* KS Function Begin */
if (flg) {
nbrofshift = shift[iter-1];
for (i = 0; i < (int) nbrofshift; i++) {
temp1 = kwork[0];
temp2 = kwork[28];
for (j = 0; j < 27; j++) {
kwork[j] = kwork[j+1];
kwork[j+28] = kwork[j+29];
}
kwork[27] = temp1;
kwork[55] = temp2;
}
} else if (iter > 1) {
nbrofshift = shift[17-iter];
for (i = 0; i < (int) nbrofshift; i++) {
temp1 = kwork[27];
temp2 = kwork[55];
for (j = 27; j > 0; j–) {
kwork[j] = kwork[j-1];
kwork[j+28] = kwork[j+27];
}
kwork[0] = temp1;
kwork[28] = temp2;
}
}

/* Permute kwork – PC2 */
kn[ 0] = kwork[13];
kn[ 1] = kwork[16];
kn[ 2] = kwork[10];
kn[ 3] = kwork[23];
kn[ 4] = kwork[ 0];
kn[ 5] = kwork[ 4];
kn[ 6] = kwork[ 2];
kn[ 7] = kwork[27];
kn[ 8] = kwork[14];
kn[ 9] = kwork[ 5];
kn[10] = kwork[20];
kn[11] = kwork[ 9];
kn[12] = kwork[22];
kn[13] = kwork[18];
kn[14] = kwork[11];
kn[15] = kwork[ 3];
kn[16] = kwork[25];
kn[17] = kwork[ 7];
kn[18] = kwork[15];
kn[19] = kwork[ 6];
kn[20] = kwork[26];
kn[21] = kwork[19];
kn[22] = kwork[12];
kn[23] = kwork[ 1];
kn[24] = kwork[40];
kn[25] = kwork[51];
kn[26] = kwork[30];
kn[27] = kwork[36];
kn[28] = kwork[46];
kn[29] = kwork[54];
kn[30] = kwork[29];
kn[31] = kwork[39];
kn[32] = kwork[50];
kn[33] = kwork[44];
kn[34] = kwork[32];
kn[35] = kwork[47];
kn[36] = kwork[43];
kn[37] = kwork[48];
kn[38] = kwork[38];
kn[39] = kwork[55];
kn[40] = kwork[33];
kn[41] = kwork[52];
kn[42] = kwork[45];
kn[43] = kwork[41];
kn[44] = kwork[49];
kn[45] = kwork[35];
kn[46] = kwork[28];
kn[47] = kwork[31];
/* KS Function End */

/* worka XOR kn */
for (i = 0; i < 48; i++)
worka = worka ^ kn;

/* 8 s-functions */
valindex = s1[2*worka[ 0]+worka[ 5]]
[2*(2*(2*worka[ 1]+worka[ 2])+
worka[ 3])+worka[ 4]];
valindex = valindex * 4;
kn[ 0] = binary[0+valindex];
kn[ 1] = binary[1+valindex];
kn[ 2] = binary[2+valindex];
kn[ 3] = binary[3+valindex];
valindex = s2[2*worka[ 6]+worka[11]]
[2*(2*(2*worka[ 7]+worka[ 8])+
worka[ 9])+worka[10]];
valindex = valindex * 4;
kn[ 4] = binary[0+valindex];
kn[ 5] = binary[1+valindex];
kn[ 6] = binary[2+valindex];
kn[ 7] = binary[3+valindex];
valindex = s3[2*worka[12]+worka[17]]
[2*(2*(2*worka[13]+worka[14])+
worka[15])+worka[16]];
valindex = valindex * 4;
kn[ 8] = binary[0+valindex];
kn[ 9] = binary[1+valindex];
kn[10] = binary[2+valindex];
kn[11] = binary[3+valindex];
valindex = s4[2*worka[18]+worka[23]]
[2*(2*(2*worka[19]+worka[20])+
worka[21])+worka[22]];
valindex = valindex * 4;
kn[12] = binary[0+valindex];
kn[13] = binary[1+valindex];
kn[14] = binary[2+valindex];
kn[15] = binary[3+valindex];
valindex = s5[2*worka[24]+worka[29]]
[2*(2*(2*worka[25]+worka[26])+
worka[27])+worka[28]];
valindex = valindex * 4;
kn[16] = binary[0+valindex];
kn[17] = binary[1+valindex];
kn[18] = binary[2+valindex];
kn[19] = binary[3+valindex];
valindex = s6[2*worka[30]+worka[35]]
[2*(2*(2*worka[31]+worka[32])+
worka[33])+worka[34]];
valindex = valindex * 4;
kn[20] = binary[0+valindex];
kn[21] = binary[1+valindex];
kn[22] = binary[2+valindex];
kn[23] = binary[3+valindex];
valindex = s7[2*worka[36]+worka[41]]
[2*(2*(2*worka[37]+worka[38])+
worka[39])+worka[40]];
valindex = valindex * 4;
kn[24] = binary[0+valindex];
kn[25] = binary[1+valindex];
kn[26] = binary[2+valindex];
kn[27] = binary[3+valindex];
valindex = s8[2*worka[42]+worka[47]]
[2*(2*(2*worka[43]+worka[44])+
worka[45])+worka[46]];
valindex = valindex * 4;
kn[28] = binary[0+valindex];
kn[29] = binary[1+valindex];
kn[30] = binary[2+valindex];
kn[31] = binary[3+valindex];

/* Permute – P */
worka[ 0] = kn[15];
worka[ 1] = kn[ 6];
worka[ 2] = kn[19];
worka[ 3] = kn[20];
worka[ 4] = kn[28];
worka[ 5] = kn[11];
worka[ 6] = kn[27];
worka[ 7] = kn[16];
worka[ 8] = kn[ 0];
worka[ 9] = kn[14];
worka[10] = kn[22];
worka[11] = kn[25];
worka[12] = kn[ 4];
worka[13] = kn[17];
worka[14] = kn[30];
worka[15] = kn[ 9];
worka[16] = kn[ 1];
worka[17] = kn[ 7];
worka[18] = kn[23];
worka[19] = kn[13];
worka[20] = kn[31];
worka[21] = kn[26];
worka[22] = kn[ 2];
worka[23] = kn[ 8];
worka[24] = kn[18];
worka[25] = kn[12];
worka[26] = kn[29];
worka[27] = kn[ 5];
worka[28] = kn[21];
worka[29] = kn[10];
worka[30] = kn[ 3];
worka[31] = kn[24];

/* bufout XOR worka */
for (i = 0; i < 32; i++) {
bufout[i+32] = bufout ^ worka;
bufout = buffer;
}
} /* End of Iter */

/* Prepare Output */
for (i = 0; i < 32; i++) {
j = bufout;
bufout = bufout[32+i];
bufout[32+i] = j;
}

/* Inverse Initial Permutation */
buffer[ 0] = bufout[39];
buffer[ 1] = bufout[ 7];
buffer[ 2] = bufout[47];
buffer[ 3] = bufout[15];
buffer[ 4] = bufout[55];
buffer[ 5] = bufout[23];
buffer[ 6] = bufout[63];
buffer[ 7] = bufout[31];
buffer[ 8] = bufout[38];
buffer[ 9] = bufout[ 6];
buffer[10] = bufout[46];
buffer[11] = bufout[14];
buffer[12] = bufout[54];
buffer[13] = bufout[22];
buffer[14] = bufout[62];
buffer[15] = bufout[30];
buffer[16] = bufout[37];
buffer[17] = bufout[ 5];
buffer[18] = bufout[45];
buffer[19] = bufout[13];
buffer[20] = bufout[53];
buffer[21] = bufout[21];
buffer[22] = bufout[61];
buffer[23] = bufout[29];
buffer[24] = bufout[36];
buffer[25] = bufout[ 4];
buffer[26] = bufout[44];
buffer[27] = bufout[12];
buffer[28] = bufout[52];
buffer[29] = bufout[20];
buffer[30] = bufout[60];
buffer[31] = bufout[28];
buffer[32] = bufout[35];
buffer[33] = bufout[ 3];
buffer[34] = bufout[43];
buffer[35] = bufout[11];
buffer[36] = bufout[51];
buffer[37] = bufout[19];
buffer[38] = bufout[59];
buffer[39] = bufout[27];
buffer[40] = bufout[34];
buffer[41] = bufout[ 2];
buffer[42] = bufout[42];
buffer[43] = bufout[10];
buffer[44] = bufout[50];
buffer[45] = bufout[18];
buffer[46] = bufout[58];
buffer[47] = bufout[26];
buffer[48] = bufout[33];
buffer[49] = bufout[ 1];
buffer[50] = bufout[41];
buffer[51] = bufout[ 9];
buffer[52] = bufout[49];
buffer[53] = bufout[17];
buffer[54] = bufout[57];
buffer[55] = bufout[25];
buffer[56] = bufout[32];
buffer[57] = bufout[ 0];
buffer[58] = bufout[40];
buffer[59] = bufout[ 8];
buffer[60] = bufout[48];
buffer[61] = bufout[16];
buffer[62] = bufout[56];
buffer[63] = bufout[24];

j = 0;
for (i = 0; i < 8; i++) {
*(dest + i) = 0×00;
for (k = 0; k < 7; k++)
*(dest + i) = ((*(dest + i)) + buffer[j+k]) * 2;
*(dest + i) = *(dest + i) + buffer[j+7];
j += 8;
}
}