md5加密算法c语言实现

以下是一个用C语言实现的MD5加密算法的示例：

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

#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32 - (c))))

void md5(uint8_t *initial_msg, size_t initial_len) {
    uint32_t h0, h1, h2, h3;
    uint8_t *msg = NULL;
    uint32_t *w = NULL;
    uint32_t a, b, c, d, i, f, g, temp;
    size_t new_len, offset;

    // 初始化变量
    h0 = 0x67452301;
    h1 = 0xEFCDAB89;
    h2 = 0x98BADCFE;
    h3 = 0x10325476;

    // 对消息进行预处理
    new_len = ((((initial_len + 8) / 64) + 1) * 64);
    msg = (uint8_t *)malloc(new_len);
    memcpy(msg, initial_msg, initial_len);
    msg[initial_len] = 128;
    offset = initial_len + 1;
    while (offset < new_len - 8) {
        msg[offset] = 0;
        offset++;
    }
    uint64_t bits_len = (uint64_t)initial_len * 8;
    memcpy(msg + new_len - 8, &bits_len, 8);

    // 处理消息的每个块
    for (offset = 0; offset < new_len; offset += 64) {
        w = (uint32_t *)(msg + offset);

        // 初始化散列值
        a = h0;
        b = h1;
        c = h2;
        d = h3;

        // 主循环
        for (i = 0; i < 64; i++) {
            if (i < 16) {
                f = (b & c) | ((~b) & d);
                g = i;
            } else if (i < 32) {
                f = (d & b) | ((~d) & c);
                g = (5 * i + 1) % 16;
            } else if (i < 48) {
                f = b ^ c ^ d;
                g = (3 * i + 5) % 16;
            } else {
                f = c ^ (b | (~d));
                g = (7 * i) % 16;
            }

            temp = d;
            d = c;
            c = b;
            b = b + LEFTROTATE((a + f + k[i] + w[g]), r[i]);
            a = temp;
        }

        // 更新散列值
        h0 += a;
        h1 += b;
        h2 += c;
        h3 += d;
    }

    // 释放内存
    free(msg);

    // 输出散列值
    printf("MD5 Hash: %08x%08x%08x%08x\n", h0, h1, h2, h3);
}

int main() {
    char *msg = "Hello, world!";
    size_t len = strlen(msg);

    md5((uint8_t *)msg, len);

    return 0;
}