Data Encryption Standard(DES) 数据加密标准算法描述。

矫情吗；* 2022-09-18 09:59 169阅读 0赞

**Data Encryption Standard(DES)** **数据加密标准算法描述**

一、算法介绍

DES算法是一种用56位密钥来加密64位数据的对称密钥算法。

DES算法的入口参数有三个：Key、Data、Mode。其中Key为8个字节共64位，是DES算法的工作密钥；Data也为8个字节64位，是要被加密或被解密的数据；

Mode为DES的工作方式，有两种：加密或解密。

二、实现步骤

1.变换密钥

A 将8字节密钥转换为64字节字串,不足则补0(或自定义)

B 根据pc1进行变换成56字节

C 将56字节密钥分为左右两部分C\[0\],D\[0\]

D 循环16次(i从1开始)

1)左移固定位数得到C\[i\]和D\[i\];

2)将C\[i\]D\[i\]用pc2化简为48位k\[i\];

2.数据处理

A 将8字节数据转换为64字节字串，不足则补0(或自定义)

B 将64字节数据转换为两部分L\[0\],R\[0\]

C 循环16次(i从1开始)，用密钥加密数据

1)将32位的R\[i-1\]按exp扩展为48位的E\[i-1\];

2)异或E\[i-1\]和K\[i\];

3)将异或结果分为8个6位长的部分B\[8\]

4)循环用S表替换(j从1开始)

a)B\[j\]第1位和第6位组合为M，作为S\[j\]的行号

b)B\[j\]第2到5位组合为N，作为S\[j\]的列号

c)用S\[j\]\[M\]\[N\]来取代B\[j\]

5)将B\[1\]到B\[8\]按P组合得到p

6)R\[i\] = p xor L\[i-1\];

7)L\[i\] = R\[i-1\];

3.组合变换后的R\[16\]L\[16\]按ip\_1变换得到最后结果

三、注意事项

1. 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.

2. 在DES密钥Key的使用、管理及密钥更换的过程中,应绝对避开DES 算法的应用误区,即:绝对不能把Key的第8,16,24......64位作为有效数据位来对Key进行管理

四、实现源码

int DES(
    		unsigned char *bufferin,
    		unsigned char *bufferout, 
    		unsigned char *key,
    		long mode)
    {
    	//密钥变换为56字节(去掉校验位)
    	static unsigned char pc1[56] = {
    		56, 48, 40, 32, 24, 16, 8, 
    		0, 57, 49, 41, 33, 25, 17, 
    		9, 1, 58, 50, 42, 34, 26, 
    		18, 10, 2, 59, 51, 43, 35, 
    		62, 54, 46, 38, 30, 22, 14, 
    		6, 61, 53, 45, 37, 29, 21, 
    		13, 5, 60, 52, 44, 36, 28, 
    		20, 12, 4, 27, 19, 11, 3 }; 
    
    	//56字节变换为48 字节(数据压缩)
    	static unsigned char pc2[48] = {
    		13, 16, 10, 23, 0, 4, 
    		2, 27, 14, 5, 20, 9, 
    		22, 18, 11, 3, 25, 7, 
    		15, 6, 26, 19, 12, 1, 
    		40, 51, 30, 36, 46, 54, 
    		29, 39, 50, 44, 32, 47, 
    		43, 48, 38, 55, 33, 52, 
    		45, 41, 49, 35, 28, 31 };
    
    	//32字节变换为48字节(数据扩展)
    	static unsigned char exp[48] = {
    		31, 0, 1, 2, 3, 4, 
    		3, 4, 5, 6, 7, 8, 
    		7, 8, 9, 10, 11, 12, 
    		11, 12, 13, 14, 15, 16, 
    		15, 16, 17, 18, 19, 20, 
    		19, 20, 21, 22, 23, 24, 
    		23, 24, 25, 26, 27, 28, 
    		27, 28, 29, 30, 31, 0 };
    
    	//64位数据IP(Initial Permutation)变换表
    	static unsigned char ip[64] = {
    		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, 
    		56, 48, 40, 32, 24, 16, 8, 0, 
    		58, 50, 42, 34, 26, 18, 10, 2, 
    		60, 52, 44, 36, 28, 20, 12, 4, 
    		62, 54, 46, 38, 30, 22, 14, 6 };
    
    	//数据逆置换(Final Permutation)
    	static unsigned char ip_1[64] = {
    		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, 
    		32, 0, 40, 8, 48, 16, 56, 24 };
    
    	//Permutation P
    	static unsigned char pp[32] = {
    		15, 6, 19, 20, 
    		28, 11, 27, 16, 
    		0, 14, 22, 25, 
    		4, 17, 30, 9, 
    		1, 7, 23, 13, 
    		31, 26, 2, 8, 
    		18, 12, 29, 5, 
    		21, 10, 3, 24 };
    
    	/* 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 };
    
    	/* 密钥生成中的循环左移位的累计次数*/
    	static unsigned char totrot[] = {
    		1, 2, 4, 6, 8, 10, 12, 14, 15, 17, 19, 21, 23, 25, 27, 28 };
    
    	/*----------------------------------------------*/
    	//long mode = 1;                                //模式，1：加密，2：解密
    	//unsigned char bufferin[9], bufferout[9];      //明文，密文
    	/*----------------------------------------------*/
    	long i, j, k; 
    	long rotshift;                              //密钥移位次数 
    	//long keylen, buflen;                      //密钥长度,明文长度 
    	unsigned char keybuf[65];                   //密钥，密钥64字节缓冲区
    	unsigned char keyreal[57], keys[17][49];    //实际使用56字节密钥,48字节密钥数组 
    	unsigned char srcbuf[65], dstbuf[65];       //明文，密文64字节缓冲区
    	unsigned char L[17][33], R[17][33], LR[65], RL[65];    //加密时临时数据左右两部分
    	unsigned char E[17][49];                    //R数组的扩展数据
    	unsigned char B[9][7], BB[33], P[33];       //E和K异或后的缓冲数组
    	unsigned char C[17][29], D[17][29], CD[57]; //56字节密钥的左右两部分
    	unsigned char temp1, temp2, m, n, x;
    
    	//1.变换密钥
    	//密钥不足8字节则用0补足(或自定义)
    	//keylen = strlen((const char*)key);
    	//if(keylen<8) 
    	// memset(key+keylen, 0, (8-keylen)); 
    	//将8字节密钥转换为64字节字串 
    	for(i=0;i<8;i++)
    	{
    		j = *(key+i);
    		keybuf[8*i] = (j / 128) % 2;
    		keybuf[8*i+1] = (j / 64) % 2;
    		keybuf[8*i+2] = (j / 32) % 2;
    		keybuf[8*i+3] = (j / 16) % 2;
    		keybuf[8*i+4] = (j / 8) % 2;
    		keybuf[8*i+5] = (j / 4) % 2;
    		keybuf[8*i+6] = (j / 2) % 2;
    		keybuf[8*i+7] = (j / 1) % 2;
    	}
    
    	//根据pc1进行变换成56字节，去掉奇偶校验位
    	for(i=0;i<56;i++)
    	{
    		keyreal[i] = keybuf[pc1[i]];
    	}
    
    	//将56字节密钥分为左右两部分C[0],D[0]
    	for(i=0;i<28;i++)
    	{
    		C[0][i] = keyreal[i];
    		D[0][i] = keyreal[i+28];
    	} 
    
    	//循环16次(i从1开始)
    	for(i=1;i<17;i++)
    	{
    		//根据加密或解密确定密钥顺序
    		if(mode)    //加密
    			rotshift = totrot[i-1];
    		else        //解密
    			rotshift = totrot[16-i];
    
    		//1)左移固定位数得到C[i]和D[i];
    		for(j=0;j<28;j++)
    		{
    			C[i][j] = C[0][j];
    			D[i][j] = D[0][j];
    		}
    		for(j=0;j < rotshift;j++)
    		{
    			temp1 = C[i][0];
    			temp2 = D[i][0];
    			for(k=0;k<27;k++)
    			{
    				C[i][k] = C[i][k+1];
    				D[i][k] = D[i][k+1];
    			}
    			C[i][27] = temp1;
    			D[i][27] = temp2;
    		} 
    
    		//2)将C[i]D[i]用pc2化简为48位k[i];
    		for(j=0;j<28;j++)
    		{
    			CD[j] = C[i][j];
    			CD[j+28] = D[i][j];
    		}
    		for(j=0;j<48;j++)
    		{
    			keys[i][j] = CD[pc2[j]];
    		}
    	}
    
    	//2.数据处理
    	//若明文不足8字节则补0(或自定义)
    	//buflen = strlen((const char*)bufferin);
    	//if(buflen<8)
    	// memset(bufferin+buflen, 0, (8-buflen));
    	//将8字节数据转换为64字节字串
    	for(i=0;i<8;i++)
    	{
    		j = *(bufferin+i);
    		srcbuf[i*8] = (j / 128) % 2;
    		srcbuf[i*8+1] = (j / 64) % 2;
    		srcbuf[i*8+2] = (j / 32) % 2;
    		srcbuf[i*8+3] = (j / 16) % 2;
    		srcbuf[i*8+4] = (j / 8) % 2;
    		srcbuf[i*8+5] = (j / 4) % 2;
    		srcbuf[i*8+6] = (j / 2) % 2;
    		srcbuf[i*8+7] = (j / 1) % 2;
    	}
    
    	//将srcbuf按ip进行变换
    	for(i=0;i<64;i++)
    		LR[i] = srcbuf[ip[i]];
    
    	//将64字节数据转换为两部分L[0],R[0]
    	for(i=0;i<32;i++)
    	{
    		L[0][i] = LR[i];
    		R[0][i] = LR[i+32];
    	}
    
    	//循环16次(i从1开始)，用密钥加密数据
    	for(i=1;i<17;i++)
    	{
    		//1)将32位的R[i-1]按exp扩展为48位的E[i-1];
    		for(j=0;j<48;j++)
    		{
    			E[i-1][j] = R[i-1][exp[j]];
    		}
    
    		//2)异或E[i-1]和K[i];
    		for(j=0;j<48;j++)
    		{
    			keys[i][j] = keys[i][j] ^ E[i-1][j];
    		}
    
    		//3)将异或结果分为8个6位长的部分B[8]
    		for(j=0;j<8;j++)
    		{
    			B[j][0] = keys[i][j*6];
    			B[j][1] = keys[i][j*6+1];
    			B[j][2] = keys[i][j*6+2];
    			B[j][3] = keys[i][j*6+3];
    			B[j][4] = keys[i][j*6+4];
    			B[j][5] = keys[i][j*6+5];
    		}
    
    		//4)循环用S表替换(j从1开始)
    		for(j=0;j<8;j++)
    		{
    			//a)B[j]第1位和第6位组合为M，作为S[j]的行号
    			m = 2 * B[j][0] + B[j][5]; 
    
    			//b)B[j]第2到5位组合为N，作为S[j]的列号
    			n = 2 * (2 * (2 * B[j][1] + B[j][2]) + B[j][3]) + B[j][4];
    
    			//c)用S[j][M][N]来取代B[j]
    			switch(j)
    			{
    			case 0:
    				x = s1[m][n];
    				break;
    			case 1:
    				x = s2[m][n];
    				break;
    			case 2:
    				x = s3[m][n];
    				break;
    			case 3:
    				x = s4[m][n];
    				break;
    			case 4:
    				x = s5[m][n];
    				break;
    			case 5:
    				x = s6[m][n];
    				break;
    			case 6:
    				x = s7[m][n];
    				break;
    			case 7:
    				x = s8[m][n];
    				break;
    			}
    			BB[j*4] = (x / 8) % 2;
    			BB[j*4 + 1] = (x / 4) % 2;
    			BB[j*4 + 2] = (x / 2) % 2;
    			BB[j*4 + 3] = (x / 1) % 2;
    		}
    
    		//5)将B[1]到B[8]按P组合得到p
    		for(j=0;j<32;j++)
    		{
    			P[j] = BB[pp[j]];
    		}
    
    		//6)R[i] = p xor L[i-1];L[i] = R[i-1];
    		for(j=0;j<32;j++)
    		{
    			R[i][j] = P[j] ^ L[i-1][j]; 
    			L[i][j] = R[i-1][j];
    		} 
    	}
    
    	//3.组合变换后的R[16]L[16]按ip_1变换得到最后结果
    	for(i=0;i<32;i++)
    	{
    		RL[i] = R[16][i];
    		RL[i+32] = L[16][i];
    	}
    	for(i=0;i<64;i++)
    	{
    		dstbuf[i] = RL[ip_1[i]];
    	}
    
    	//将64字节数据转换为8字节
    	for (i = 0; i < 8; i++) 
    	{
    		*(bufferout + i) = 0x00;
    		for (k = 0; k < 7; k++)
    			*(bufferout + i) = ((*(bufferout + i)) + dstbuf[8*i+k]) * 2;
    		*(bufferout + i) = *(bufferout + i) + dstbuf[8*i+7];
    	}
    	return 0;
    }

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