C语言编写DES算法，并注释

以下是C语言编写的DES算法，其中包含注释：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// 初始置换表
const int IP_Table[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 };

// 逆初始置换表
const int IP_1_Table[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 };

// 扩展置换表
const int E_Table[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 };

// S盒
const int S_Box[8][4][16] = { 
    // 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 }
    }
};

// 置换P
const int P_Table[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 };

// 密钥置换表，将64位密钥变成56位密钥
const int Key_Table[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 };

// 压缩置换表，将56位密钥压缩成48位密钥
const int Key_Table_Compress[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 };

// 左移位数表
const int Move_Table[16] = { 1, 1, 2, 2, 
                              2, 2, 2, 2, 
                              1, 2, 2, 2, 
                              2, 2, 2, 1 };

// 存储16个子密钥
int Sub_Key[16][48];

// 将64位明文和64位密钥进行DES加密
void DES_Encrypt(char *plaintext, char *key, char *ciphertext)
{
    // 将明文和密钥转换为二进制
    int plaintextBits[64], keyBits[64];
    memset(plaintextBits, 0, sizeof(plaintextBits));
    memset(keyBits, 0, sizeof(keyBits));
    for (int i = 0; i < 8; i++)
    {
        for (int j = 0; j < 8; j++)
        {
            plaintextBits[i * 8 + j] = (plaintext[i] >> (7 - j)) & 1;
            keyBits[i * 8 + j] = (key[i] >> (7 - j)) & 1;
        }
    }

    // 生成16个子密钥
    int left[28], right[28];
    for (int i = 0; i < 28; i++)
    {
        left[i] = keyBits[Key_Table[i] - 1];
        right[i] = keyBits[Key_Table[i + 28] - 1];
    }
    for (int i = 0; i < 16; i++)
    {
        // 左移
        for (int j = 0; j < Move_Table[i]; j++)
        {
            int temp = left[0];
            for (int k = 0; k < 27; k++)
            {
                left[k] = left[k + 1];
            }
            left[27] = temp;
            temp = right[0];
            for (int k = 0; k < 27; k++)
            {
                right[k] = right[k + 1];
            }
            right[27] = temp;
        }
        // 压缩置换
        for (int j = 0; j < 48; j++)
        {
            if (Key_Table_Compress[j] <= 28)
            {
                Sub_Key[i][j] = left[Key_Table_Compress[j] - 1];
            }
            else
            {
                Sub_Key[i][j] = right[Key_Table_Compress[j] - 29];
            }
        }
    }

    // 初始置换
    int tempBits[64];
    memset(tempBits, 0, sizeof(tempBits));
    for (int i = 0; i < 64; i++)
    {
        tempBits[i] = plaintextBits[IP_Table[i] - 1];
    }
    // 进行16轮加密
    int leftBits[32], rightBits[32];
    memcpy(leftBits, tempBits, sizeof(leftBits));
    memcpy(rightBits, tempBits + 32, sizeof(rightBits));
    for (int i = 0; i < 16; i++)
    {
        int temp[32];
        memcpy(temp, leftBits, sizeof(temp));
        // F函数
        for (int j = 0; j < 32; j++)
        {
            leftBits[j] = rightBits[j];
            rightBits[j] = temp[j] ^ S_Box[j / 4][((Sub_Key[i][j * 6] << 1) + Sub_Key[i][j * 6 + 5])][((Sub_Key[i][j * 6 + 1] << 3) + (Sub_Key[i][j * 6 + 2] << 2) + (Sub_Key[i][j * 6 + 3] << 1) + Sub_Key[i][j * 6 + 4])];
        }
    }
    // 合并左右部分
    memcpy(tempBits, rightBits, sizeof(rightBits));
    memcpy(tempBits + 32, leftBits, sizeof(leftBits));
    // 逆初始置换
    for (int i = 0; i < 64; i++)
    {
        ciphertext[i / 8] |= tempBits[IP_1_Table[i] - 1] << (7 - i % 8);
    }
}

int main()
{
    char plaintext[] = "0123456789ABCDEF";
    char key[] = "133457799BBCDFF1";
    char ciphertext[16] = { 0 };
    DES_Encrypt(plaintext, key, ciphertext);
    printf("Ciphertext: ");
    for (int i = 0; i < 16; i++)
    {
        printf("%02X", ciphertext[i]);
    }
    return 0;
}

注释中详细解释了DES算法的各个部分，包括置换表、S盒、子密钥生成、加密过程等。