des密码算法c语言

DES（Data Encryption Standard）是一种对称加密算法，它使用相同的密钥进行加密和解密。

以下是使用C语言实现DES密码算法的代码示例：

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

#define ENCRYPT_MODE 1
#define DECRYPT_MODE 0

/* 初始置换表 */
static const uint8_t ip_table[] = {
    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 */
static const uint8_t inv_ip_table[] = {
    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
};

/* 选择置换表 */
static const uint8_t pc1_table[] = {
    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 */
static const uint8_t pc2_table[] = {
    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
};

/* 扩展置换表 */
static const uint8_t expand_table[] = {
    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 */
static const uint8_t s_box[8][64] = {{
    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
}};

/* P盒 */
static const uint8_t p_table[] = {
    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
};

/* 每轮左移的位数 */
static const uint8_t shift_table[] = {
    1, 1, 2, 2, 2, 2, 2, 2,
    1, 2, 2, 2, 2, 2, 2, 1
};

/* 64位密钥 */
typedef struct {
    uint8_t data[8];
} des_key_t;

/* 64位数据块 */
typedef struct {
    uint8_t data[8];
} des_data_t;

/* 48位子密钥 */
typedef struct {
    uint8_t data[6];
} des_subkey_t;

/* 以二进制形式打印数据 */
static void print_binary(const uint8_t *data, int len)
{
    for (int i = 0; i < len; i++) {
        for (int j = 7; j >= 0; j--) {
            printf("%d", (data[i] >> j) & 1);
        }
    }
}

/* 执行置换操作 */
static void permute(const uint8_t *src, uint8_t *dst, const uint8_t *table, int len)
{
    memset(dst, 0, len);
    for (int i = 0; i < len * 8; i++) {
        int pos = table[i] - 1;
        int byte_pos = pos / 8;
        int bit_pos = pos % 8;
        dst[i / 8] |= ((src[byte_pos] >> (7 - bit_pos)) & 1) << (7 - i % 8);
    }
}

/* 生成子密钥 */
static void generate_subkey(const des_key_t *key, des_subkey_t *subkeys)
{
    uint8_t temp[56];
    uint8_t *left = temp, *right = temp + 28;
    uint8_t *out = subkeys->data;

    /* 初步置换 */
    permute(key->data, temp, pc1_table, 7);

    for (int i = 0; i < 16; i++) {
        /* 左移 */
        int shift = shift_table[i];
        uint8_t temp_left = left[0], temp_right = right[0];
        for (int j = 0; j < 27; j++) {
            left[j] = left[j + 1];
            right[j] = right[j + 1];
        }
        left[27] = temp_left;
        right[27] = temp_right;

        /* 压缩置换生成子密钥 */
        permute(temp, out, pc2_table, 6);
        out += 6;
    }
}

/* S盒代替操作 */
static uint8_t s_box_replace(uint8_t input, const uint8_t *s_box)
{
    uint8_t row = ((input & 0x20) >> 4) | (input & 1);
    uint8_t col = (input & 0x1e) >> 1;
    return s_box[row * 16 + col];
}

/* F函数 */
static void f(const uint8_t *right, const des_subkey_t *subkey, uint8_t *out)
{
    uint8_t temp[6], expanded[6], s_boxed[4];
    uint32_t result = 0;

    /* 扩展置换 */
    permute(right, expanded, expand_table, 6);

    /* 与子密钥异或 */
    for (int i = 0; i < 6; i++) {
        temp[i] = expanded[i] ^ subkey->data[i];
    }

    /* S盒代替操作 */
    s_boxed[0] = s_box_replace(temp[0] >> 2, s_box[0]);
    s_boxed[1] = s_box_replace(((temp[0] & 3) << 4) | (temp[1] >> 4), s_box[1]);
    s_boxed[2] = s_box_replace(((temp[1] & 0xf) << 2) | (temp[2] >> 6), s_box[2]);
    s_boxed[3] = s_box_replace