哈希算法MD5实现 c语言并给代码注释

好的，下面是哈希算法MD5在C语言中的实现，附有代码注释：

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

// 定义常量，用于实现MD5算法中的一些位运算操作
#define leftrotate(x, c) (((x) << (c)) | ((x) >> (32 - (c))))
#define F(x, y, z) (((x) & (y)) | (~(x) & (z)))
#define G(x, y, z) (((x) & (z)) | ((y) & ~(z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))
#define I(x, y, z) ((y) ^ ((x) | ~(z)))

// 定义T表，用于实现MD5算法中的循环左移和每轮运算使用的常量
const uint32_t T[] = {
    0xd76aa478, 0xe8c7b756, 0x242070db, 0xc1bdceee,
    0xf57c0faf, 0x4787c62a, 0xa8304613, 0xfd469501,
    0x698098d8, 0x8b44f7af, 0xffff5bb1, 0x895cd7be,
    0x6b901122, 0xfd987193, 0xa679438e, 0x49b40821,
    0xf61e2562, 0xc040b340, 0x265e5a51, 0xe9b6c7aa,
    0xd62f105d, 0x02441453, 0xd8a1e681, 0xe7d3fbc8,
    0x21e1cde6, 0xc33707d6, 0xf4d50d87, 0x455a14ed,
    0xa9e3e905, 0xfcefa3f8, 0x676f02d9, 0x8d2a4c8a,
    0xfffa3942, 0x8771f681, 0x6d9d6122, 0xfde5380c,
    0xa4beea44, 0x4bdecfa9, 0xf6bb4b60, 0xbebfbc70,
    0x289b7ec6, 0xeaa127fa, 0xd4ef3085, 0x04881d05,
    0xd9d4d039, 0xe6db99e5, 0x1fa27cf8, 0xc4ac5665,
    0xf4292244, 0x432aff97, 0xab9423a7, 0xfc93a039,
    0x655b59c3, 0x8f0ccc92, 0xffeff47d, 0x85845dd1,
    0x6fa87e4f, 0xfe2ce6e0, 0xa3014314, 0x4e0811a1,
    0xf7537e82, 0xbd3af235, 0x2ad7d2bb, 0xeb86d391};

// 将输入数据转换为MD5算法所需的格式
void md5_transform(uint32_t state[], const uint8_t block[]) {
    uint32_t a = state[0], b = state[1], c = state[2], d = state[3], x[16];

    // 将每个分组的数据分成16个32位的小块，并按小端序合并到一个数组x中
    for (int i = 0, j = 0; i < 16; ++i, j += 4)
        x[i] = (uint32_t) ((block[j]) | (block[j + 1] << 8) | (block[j + 2] << 16) | (block[j + 3] << 24));

    // 第一轮循环
    for (int i = 0; i < 16; ++i) {
        uint32_t temp = F(b, c, d);
        temp += a + x[i] + T[i];
        a = d;
        d = c;
        c = b;
        b += leftrotate(temp, 7);
    }

    // 第二轮循环
    for (int i = 16; i < 32; ++i) {
        uint32_t temp = G(b, c, d);
        temp += a + x[(5 * i + 1) % 16] + T[i];
        a = d;
        d = c;
        c = b;
        b += leftrotate(temp, 12);
    }

    // 第三轮循环
    for (int i = 32; i < 48; ++i) {
        uint32_t temp = H(b, c, d);
        temp += a + x[(3 * i + 5) % 16] + T[i];
        a = d;
        d = c;
        c = b;
        b += leftrotate(temp, 17);
    }

    // 第四轮循环
    for (int i = 48; i < 64; ++i) {
        uint32_t temp = I(b, c, d);
        temp += a + x[(7 * i) % 16] + T[i];
        a = d;
        d = c;
        c = b;
        b += leftrotate(temp, 22);
    }

    // 将本轮的结果与之前处理的结果合并
    state[0] += a;
    state[1] += b;
    state[2] += c;
    state[3] += d;
}

// 根据输入的字符串计算MD5值
void md5_hash(const uint8_t *initial_msg, size_t initial_len, uint8_t *digest) {

    // 预处理
    uint8_t msg[initial_len + 1];
    memcpy(msg, initial_msg, initial_len);
    msg[initial_len] = 0x80;
    size_t new_len = (((initial_len + 8) >> 6) + 1) << 6;
    uint8_t padding[new_len - initial_len - 1];
    memset(padding, 0, new_len - initial_len - 1);
    uint64_t bit_len = 8 * initial_len;
    memcpy(padding, &bit_len, 8);

    // 初始化状态
    uint32_t state[] = {0x67452301, 0xEFCDAB89, 0x98BADCFE, 0x10325476};
    size_t offset;

    // 对每个512位的分组进行处理
    for (offset = 0; offset < new_len; offset += 64)
        md5_transform(state, msg + offset);

    // 将结果拷贝到输出数组中
    memcpy(digest, state, 16);
}

// 主函数
int main() {
    // 测试数据
    uint8_t str[] = "hello, world!";
    uint8_t digest[16];
    md5_hash(str, strlen((char *) str), digest);

    // 输出结果，每个字节以16进制格式输出
    printf("MD5：%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x\n",
           digest[0], digest[1], digest[2], digest[3],
           digest[4], digest[5], digest[6], digest[7],
           digest[8], digest[9], digest[10], digest[11],
           digest[12], digest[13], digest[14], digest[15]);
    return 0;
}

以上就是哈希算法MD5在C语言中的实现及代码注释，希望能对您有所帮助。