DES算法C语言完整代码

DES (Data Encryption Standard) 是一种对称加密算法，用于保护数据传输的安全。在 C 语言中编写 DES 算法的完整代码比较长，因为涉及到大量的位操作和循环结构。以下是一个简化的 DES 加密函数示例，使用了 bitstring 操作库（如 `stdint.h` 和自定义函数）。请注意，实际应用中你需要链接相应的库并处理更复杂的加密流程，包括密钥处理、模式选择等。

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

// 定义 DES 密钥和块大小
#define KEY_SIZE 8
#define BLOCK_SIZE 8

void leftrotate(int32_t x, int n) {
    return (x << n) | (x >> (32 - n));
}

void sub_bytes(uint32_t *state) {
    static const uint8_t sbox[256] = { /* ... DES S-box values ... */ };
    for (int i = 0; i < 4; ++i)
        state[i] = sbox[state[i]];
}

void pbox(uint32_t *state) {
    // P-box is not necessary for a simplified explanation, but in practice it's applied here too.
    // In real code, you would define and apply the P-box like sub_bytes.
}

void expand_key(const uint8_t key[], uint32_t key_schedule[]) {
    // Key expansion routine goes here, typically using a pre-defined set of constants and operations
    // For brevity, this part is omitted.
}

void encrypt_block(uint32_t input, uint32_t key_schedule[]) {
    // DES round function (LFB), simplified here
    sub_bytes(input);
    for (int r = 1; r <= 16; ++r) {
        if (r % 2 == 0)
            input[0] ^= key_schedule[r];
        else
            for (int i = 0; i < 4; ++i)
                input[i] ^= key_schedule[r + i];
        pbox(input);
        input = leftrotate(input, 1);
    }
}

// 示例：加密一块数据
void des_encrypt(const uint8_t plaintext[BLOCK_SIZE], const uint8_t key[KEY_SIZE], uint8_t ciphertext[BLOCK_SIZE]) {
    uint32_t input[BLOCK_SIZE / sizeof(uint32_t)];
    uint32_t key_schedule[64]; // 虽然实际只需要32字节，这里为了演示扩展了空间
    expand_key(key, key_schedule);

    for (size_t i = 0; i < sizeof(input); ++i)
        input[i] = (uint32_t)plaintext[i];

    encrypt_block(input, key_schedule);
    for (size_t i = 0; i < sizeof(ciphertext); ++i)
        ciphertext[i] = (uint8_t)(input[i]);
}

int main() {
    // 测试代码，实际应用中这一步会被替换为输入/输出处理
    uint8_t plaintext[BLOCK_SIZE] = { /* ... your plaintext data ... */ };
    uint8_t key[KEY_SIZE] = { /* ... your 8-byte DES key ... */ };
    uint8_t ciphertext[BLOCK_SIZE];

    des_encrypt(plaintext, key, ciphertext);
    printf("Ciphertext: ");
    for (size_t i = 0; i < sizeof(ciphertext); ++i)
        printf("%02X ", ciphertext[i]);

    return 0;
}