如何利用MD5算法在C语言中实现数据加密？

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
// 左移操作宏定义
#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32  (c))))
// MD5算法中的四个非线性函数
#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)))
// MD5算法的主循环
void md5_main_loop(uint32_t state[4], uint32_t count[2], uint8_t buffer[64]) {
    uint32_t a, b, c, d, f, g, temp;
    uint32_t *x = (uint32_t *)buffer;
    a = state[0];
    b = state[1];
    c = state[2];
    d = state[3];
    for (int i = 0; i < 64; i++) {
        if (i < 16) {
            f = F(b, c, d);
            g = i;
        } else if (i < 32) {
            f = G(b, c, d);
            g = (5 * i + 1) % 16;
        } else if (i < 48) {
            f = H(b, c, d);
            g = (3 * i + 5) % 16;
        } else {
            f = I(b, c, d);
            g = (7 * i) % 16;
        }
        temp = d;
        d = c;
        c = b;
        b = b + LEFTROTATE((a + f + k[i] + x[g]), r[i]);
        a = temp;
    }
    state[0] += a;
    state[1] += b;
    state[2] += c;
    state[3] += d;
}
// MD5算法初始化
void md5_init(uint32_t state[4], uint32_t count[2]) {
    state[0] = 0x67452301;
    state[1] = 0xefcdab89;
    state[2] = 0x98badcfe;
    state[3] = 0x10325476;
    count[0] = count[1] = 0;
}
// MD5算法处理数据块
void md5_process_block(uint32_t state[4], uint32_t count[2], uint8_t data[64]) {
    uint32_t n = (count[0] >> 3) & 0x3F;
    uint8_t *p = data + n * 4;
    uint32_t i;
    for (i = 0; i < 16; i++, p += 4) {
        state[i] = (uint32_t)(p[0]) | ((uint32_t)(p[1]) << 8) | ((uint32_t)(p[2]) << 16) | ((uint32_t)(p[3]) << 24);
    }
    md5_main_loop(state, count, data);
}
// MD5算法更新状态和计数器
void md5_update(uint32_t state[4], uint32_t count[2], uint8_t data[], uint32_t len) {
    uint32_t i, index, partlen;
    index = (count[0] >> 3) & 0x3F;
    count[0] += len << 3;
    if (count[0] < (len << 3)) {
        count[1]++;
    }
    count[1] += len >> 29;
    partlen = 64  index;
    if (len >= partlen) {
        memcpy(&data[index], data, partlen);
        md5_process_block(state, count, data);
        for (i = partlen; i + 63 < len; i += 64) {
            md5_process_block(state, count, data + i);
        }
        index = 0;
    } else {
        i = 0;
    }
    memcpy(&data[index], data + i, len  i);
}
// MD5算法结束处理，输出结果
void md5_finish(uint32_t state[4], uint8_t digest[16]) {
    uint32_t i;
    uint8_t *p = (uint8_t *)digest;
    for (i = 0; i < 4; i++) {
        p[i] = (uint8_t)(state[i] & 0xff);
        p[i + 4] = (uint8_t)((state[i] >> 8) & 0xff);
        p[i + 8] = (uint8_t)((state[i] >> 16) & 0xff);
        p[i + 12] = (uint8_t)((state[i] >> 24) & 0xff);
    }
}
// MD5算法主函数
void md5(uint8_t data[], uint32_t len, uint8_t digest[16]) {
    uint32_t state[4], count[2];
    md5_init(state, count);
    md5_update(state, count, data, len);
    md5_finish(state, digest);
}

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