用C语言实现DES加密S盒压缩功能，且不可调用编译软件现有密码算法实现接口

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DES加密算法中的S盒压缩功能是将48位的数据压缩成32位，并进行后续的加密操作。以下是用C语言实现DES加密S盒压缩功能的示例代码：

#include <stdio.h>

// 定义S盒
int S[8][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}
    },
    {
        {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}
    },
    {
        {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}
    },
    {
        { 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}
    },
    {
        { 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}
    },
    {
        {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}
    },
    {
        { 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}
    },
    {
        {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}
    }
};

// 执行S盒压缩
void substitution(char input[48], char output[32]) {
    int i, j;
    for (i = 0; i < 8; i++) {
        int row = (input[i*6]-'0')*2 + (input[i*6+5]-'0');
        int col = (input[i*6+1]-'0')*8 + (input[i*6+2]-'0')*4 + (input[i*6+3]-'0')*2 + (input[i*6+4]-'0');
        int value = S[i][row][col];
        for (j = 0; j < 4; j++) {
            output[i*4+j] = (value >> (3-j)) & 1 ? '1' : '0';
        }
    }
}

int main() {
    char input[48] = "110001100110110010100010010101110101011010100000";
    char output[32];
    substitution(input, output);
    printf("%s -> %s\n", input, output);
    return 0;
}

在上面的代码中，我们首先定义了DES加密算法中的S盒，并编写了一个执行S盒压缩的函数`substitution`。函数接受一个长度为48的输入数据和一个长度为32的输出数据，并根据S盒将输入数据压缩成32位。最后，我们在`main`函数中测试了`substitution`函数的功能。

需要注意的是，由于我们不能调用现有的密码算法实现接口，因此上面的代码只是实现了S盒压缩功能，而不是完整的DES加密算法。如果需要实现完整的DES加密算法，还需要编写其他的函数，如初始置换、Feistel轮函数、E盒扩展、P盒置换、逆置换等。