這學期開了密碼學課，聽老師在課堂上講各種加密演算法各種高大上，但自high過後才發現別的先不說，單是DES自己看課本完全不懂。最後是在同學推薦下看了個視訊才弄懂了是怎樣一步步進行處理的，然後一時手癢就編了出來。雖然功能實現了，但程式的健壯性不是很好。目前程式是實現八位金鑰與八位明文進行加密處理，金鑰和明文從鍵盤讀入，多於八位會緩衝掉，但少於八位的我目前還沒想到怎麼處理，還有的就是實際上明文不應該有位數限制，但由於我能力有限，這些問題（說不定還有我沒發現的問題）都沒解決，各位路過的大大有解決方法的麻煩指導一下，不勝感激~~

    好了，廢話不多說了，見程式碼吧~（ps.命名不是很規範，大家將就下）

#include<stdio.h>

/*各種函式定義*/
int move_num(int r);
void xor(int *r_b, int *k3, int large);
void s_box(int r_t[32], int r_b[48]);
void erzhuanshiliu(int *k, char *key, int large);
void shizhuaner(int *k, int n, int i, int large);
void round(int r, int k2[56], int k3[48], int r_s[32], int r_b[48], int l[32], int k_c_two[48], int m_c_two[32], int e[48], char c_r[8], char c_l[8]);
void exchange(int *k1, int *k2, int *rule, int n);
void key_move(int k2[56], int n);

/*十進位制轉換成二進位制*/
void shizhuaner(int *k, int n, int i,int large)  
/* k是存放二進位制的陣列，n是需要進行轉換的十進位制數，i是第i個十進位制數，large是陣列大小*/
{
	int j;	//計數的j，沒什麼大的含義
	large = large / 8;
	j = large - 1;
	do
	{
		k[i * large + j] = n % 2;
		n = n / 2;
		j--;
	} while (n != 0);
	while (j >= 0)
	{
		k[i * large + j] = 0;
		j--;
	} 
	return ;
}

/*二進位制轉換成十六進位制*/
void erzhuanshiliu(int *k,char *key, int large) 
/* k是二進位制陣列，key是存放十六進位制的陣列，large是k陣列的大小*/
{
	int i,j; //計數的i、j，沒什麼大的含義
	large = large / 4;
	for (i = 0; i < large; i++)
	{
		j = k[i * 4] * 8 + k[i * 4 + 1] * 4 + k[i * 4 + 2] * 2 + k[i * 4 + 3];
		if (j >= 10)
		{
			switch (j)
			{
			case 10:key[i] = 'a'; break;
			case 11:key[i] = 'b'; break;
			case 12:key[i] = 'c'; break;
			case 13:key[i] = 'd'; break;
			case 14:key[i] = 'e'; break;
			case 15:key[i] = 'f'; break;
			}
		}
		else
		{
			j = j + 48;
			key[i] = (char)j;
		}
	}
	return;
}

/*迴圈函式*/
void round(int r, int k2[56], int k3[48], int r_s[32], int r_b[48], int l[32], int k_c_two[48], int m_c_two[32], int e[48], char c_r[8], char c_l[8])
/* r是輪數*/
/* k2是金鑰經過置換1置換完的陣列，k3是金鑰經過置換2置換完的陣列*/
/* r_s是明文處理中R的32大小時的陣列，r_b是明文處理中R的48大小時的陣列，l是明文處理中L的陣列*/
/* k_c_two是金鑰處理中置換2的置換規則陣列，m_c_two是明文處理中置換2的置換規則陣列，e是明文處理中e盒的置換規則陣列*/
/* c_r是各輪密文的r部分,c_l是各輪密文的l部分*/
{
	int i, n, r_t[32],r_c[32]; //計數的i，沒什麼大的含義；n儲存該輪左移的數值；r_t,r_c存放中間處理數值的32大小的陣列
	printf("這是第%d輪密文：\n", r);
	n = move_num(r); //獲取第r輪金鑰左移的位數
	key_move(k2, n); //呼叫金鑰左移函式
	exchange(k2, k3, k_c_two, 48);  //金鑰進行置換2運算
	exchange(r_s, r_b,e,48);  //明文進行e盒擴充套件置換運算
	xor(r_b, k3,48);  //經過金鑰置換2運算後的子金鑰與從e盒出來的子明文異或  
	s_box(r_t,r_b);  //呼叫明文處理中的s盒運算函式
	exchange(r_t, r_c, m_c_two, 32);  //明文進行置換2運算
	for (i = 0; i < 32; i++)
		r_t[i] = r_c[i];
	xor(r_t, l, 32);	//經過處理後的R與L異或
	for (i = 0; i < 32; i++)
		l[i] = r_s[i];  //準備下次迴圈的L
    for (i = 0; i < 32; i++)
		r_s[i] = r_t[i];  //準備下次迴圈的R
	erzhuanshiliu(r_s, c_r, 32);
	for (i = 0; i < 8; i++)
		printf("%c ", c_r[i]);  //第r輪R部分的密文 
	erzhuanshiliu(l, c_l, 32);
	for (i = 0; i < 8; i++)
		printf("%c ", c_l[i]);  //第r輪L部分的密文
	printf("\n");
	printf("\n");
	return;
}


/* 異或函式 */
void xor(int *r_b, int *k3,int large)
{
	int i;  //計數的i，沒什麼大的含義
	for (i = 0; i < large; i++)
	{
		if (r_b[i] != k3[i])  //兩數相同結果取0，兩數不同取1
			r_b[i] = 1;
		else
			r_b[i] = 0;
	}
}

/* S盒運算函式 */
void s_box(int r_t[32],int r_b[48])
{
	int i,hang,lie,jie;  //計數的i，沒什麼大的含義；hang是S盒的行下標；lie是S盒的列下標；jie是根據行、列下標查詢出的結果
	/* S1~S8盒 */
	int 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 } },
	    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 } },
	    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 } },
	    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, 3 },
	                  { 3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14 } },
	    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 } },
	    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 } },
	    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 } },
	    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 } };
	for (i = 0; i < 8; i++)
	{
		hang = r_b[i * 6] * 2 + r_b[i * 6 + 5];  //第0位與第5位決定行下標
		lie = r_b[i * 6 + 1] * 8 + r_b[i * 6 + 2] * 4 + r_b[i * 6 + 3] * 2 + r_b[i * 6 + 4];  //第1、2、3、4位決定列下標
		switch (i)  //第i個數查詢Si盒
		{
		case 0:jie = s1[hang][lie]; break;
		case 1:jie = s2[hang][lie]; break;
		case 2:jie = s3[hang][lie]; break;
		case 3:jie = s4[hang][lie]; break;
		case 4:jie = s5[hang][lie]; break;
		case 5:jie = s6[hang][lie]; break;
		case 6:jie = s7[hang][lie]; break;
		case 7:jie = s8[hang][lie]; break;
		}
		shizhuaner(r_t, jie, i,32);  //S盒為十六進位制，須轉換回二進位制進行存放
	}
}

/*左移函式*/
void key_move(int k2[56], int n)
{
	int i, one, two, twentyeight, twentynight;  //計數的i，沒什麼大的含義；one、two、twentyeight、twentynight用於存放第1、2、28、29個數
	one = k2[0];  //先記錄第1、2、28、29個數
	two = k2[1];
	twentyeight = k2[28];
	twentynight = k2[29];
	for (i = 0; i < (28 - n); i++)  //迴圈賦值
	{
		k2[i] = k2[i + n];
		k2[i + 28] = k2[i + n + 28];
	}
	if (n == 1)  //左移1位時，特殊端點值（第27、55）賦值
	{
		k2[27] = one;
		k2[55] = twentyeight;
	}
	else  //左移2位時，特殊端點值（第27、28、54、55）賦值
	{
		k2[26] = one;
		k2[27] = two;
		k2[54] = twentyeight;
		k2[55] = twentynight;
	}	
}

/* 獲取第r輪左移位數 */
int move_num(int r)
{
	int i;  //i儲存移動的位數
	switch (r)
	{
	case 1:i = 1; break;
	case 2:i = 1; break;
	case 3:i = 2; break;
	case 4:i = 2; break;
	case 5:i = 2; break;
	case 6:i = 2; break;
	case 7:i = 2; break;
	case 8:i = 2; break;
	case 9:i = 1; break;
	case 10:i = 2; break;
	case 11:i = 2; break;
	case 12:i = 2; break;
	case 13:i = 2; break;
	case 14:i = 2; break;
	case 15:i = 2; break;
	case 16:i = 1; break;
	}
	return i;  //返回移動的位數
}

/* 置換函式 */
void exchange(int *k1, int *k2, int *rule,int n)
{
	int i, j;  //計數的i，j
	for (i = 0; i < n; i++)
	{
		j = rule[i];	//根據rule陣列進行置換，也就是賦值
		k2[i] = k1[j-1];
	}
	return;
}

/*主函式*/
int main()
{ 
	/* c是最終密文，c_r是密文的R部分，c_l是密文的L的部分，g是用於緩衝掉回車符，k接收從鍵盤輸入金鑰，m接收從鍵盤輸入的明文*/
	char c[16],c_r[8],c_l[8], g, k[8], m[8]; 
	/* 計數的i，j；r是輪數；n接收型別轉換後的結果；k1，k2，k3是金鑰處理中不同大小的陣列；m1，m2是明文處理中的陣列，r_s是R 32大小時的陣列，r_b是R 48大小時的陣列，l是L的陣列*/
	int i, j, r, n, k1[64], k2[56], k3[48], m1[64], m2[64],r_s[32],r_b[48],l[32];
	/* k_c_one是金鑰處理的置換1，k_c_two是金鑰處理的置換2，m_c_one是明文處理的置換1，e是明文處理的e盒，m_c_two是明文處理的置換2 */
	int k_c_one[56] = { 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 },
		k_c_two[48] = { 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 },
		m_c_one[64] = { 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, 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 },
		e[48] = { 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 },
		m_c_two[32] = { 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 },
	  m_c_three[64] = { 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 };
	printf("**DES加密**\n");
	printf("\n");
	printf("請輸入加密的金鑰:\n");
	for (i = 0; i < 8; i++)  //從鍵盤裡獲取輸入的金鑰
	{
		scanf_s("%c", &k[i]);
		n = (int)k[i];
		shizhuaner(k1, n, i,64);  //進行金鑰進位制轉換
	}
	g = getchar();  //緩衝掉多於8個字元以外字元和回車符
	while (g != '\n')
	{
		g = getchar();
	}
	printf("請輸入需要加密的明文:\n");
	for (i = 0; i < 8; i++)  //從鍵盤裡獲取輸入的明文
	{
		scanf_s("%c", &m[i]);
		n = (int)m[i];
		shizhuaner(m1, n, i,64);  //進行明文進位制轉換
	}
	g = getchar();  //緩衝掉多於8個字元以外字元和回車符
	while (g != '\n')
	{
		g = getchar();
	}
	printf("\n");
	exchange(k1, k2, k_c_one, 56);  //金鑰進行置換1處理
	exchange(m1, m2, m_c_one, 64);  //明文進行金鑰1處理
	for (i = 0; i < 32; i++)
		l[i] = m2[i];  //明文的L部分
	j = 0;
	for (i = 32; i < 64; i++)
	{
		r_s[j] = m2[i];  //明文的R部分
		j++;
	}	
	for (r = 1; r <= 16; r++)  //進行16輪的迴圈處理
		round(r,k2, k3, r_s, r_b, l, k_c_two, m_c_two, e,  c_r, c_l);
	for (i = 0; i < 64; i++)  //將密文R的部分與密文L的部分合一起
	{
		m1[i] = r_s[i];
		if (i >= 32)
			m1[i] = l[i - 32];
	}
	exchange(m1, m2, m_c_three, 64);  //進行明文處理的置換3
	erzhuanshiliu(m2, c, 64);  //二進位制轉換成十六進位制，得到最終密文
	printf("這是最終密文:\n");
	for (i = 0; i < 16; i++)
		printf("%c ", c[i]);
	printf("\n");
	return 0;
}
 

以下是測試程式碼和執行情況的截圖：

   這是我第一次寫部落格（好緊張好刺激啊~~），請各位大大多多指教撒~~