MD5加密算法C语言实现

可以使用以下代码实现MD5加密算法的C语言实现：

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

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

void md5(char *initial_msg, size_t initial_len, char *output) {
    uint8_t msg[initial_len];
    uint32_t i, j, k;

    uint32_t h0, h1, h2, h3;
    h0 = 0x67452301;
    h1 = 0xEFCDAB89;
    h2 = 0x98BADCFE;
    h3 = 0x10325476;

    uint32_t *msg32;
    size_t new_len, offset;
    
    for (i = 0; i < initial_len; ++i) {
        msg[i] = initial_msg[i];
    }
    
    new_len = ((((uint64_t)initial_len + 8) / 64) + 1) * 64;
    msg32 = calloc(new_len, 1);

    for (i = 0; i < initial_len; ++i) {
        msg32[i >> 2] |= msg[i] << ((i % 4) * 8);
    }
    msg32[i >> 2] |= 0x80 << ((i % 4) * 8);
    msg32[new_len/4 - 2] = initial_len*8;

    for (i = 0; i < new_len; i += 64) {
        uint32_t a = h0, b = h1, c = h2, d = h3;
        uint32_t chunk[16];
        for (j = 0; j < 16; ++j) {
            chunk[j] = msg32[i/4 + j];
        }
        for (j = 0; j < 64; ++j) {
            uint32_t f, g;
            if (j < 16) {
                f = (b & c) | ((~b) & d);
                g = j;
            } else if (j < 32) {
                f = (d & b) | ((~d) & c);
                g = (5*j + 1) % 16;
            } else if (j < 48) {
                f = b ^ c ^ d;
                g = (3*j + 5) % 16;
            } else {
                f = c ^ (b | (~d));
                g = (7*j) % 16;
            }
            uint32_t temp = d;
            d = c;
            c = b;
            b = b + LEFTROTATE((a + f + 0x5A827999 + chunk[g]), 12);
            a = temp;
        }
        h0 += a;
        h1 += b;
        h2 += c;
        h3 += d;
    }

    sprintf(output, "%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x", 
        (h0>>24)&0xff, (h0>>16)&0xff, (h0>>8)&0xff, h0&0xff,
        (h1>>24)&0xff, (h1>>16)&0xff, (h1>>8)&0xff, h1&0xff,
        (h2>>24)&0xff, (h2>>16)&0xff, (h2>>8)&0xff, h2&0xff,
        (h3>>24)&0xff, (h3>>16)&0xff, (h3>>8)&0xff, h3&0xff);
}

int main(int argc, char **argv) {
    if (argc < 2) {
        printf("usage: %s 'string'\n", argv[0]);
        return 1;
    }
    char output[33];
    md5(argv[1], strlen(argv[1]), output);
    printf("%s\n", output);
    return 0;
}

请注意，这只是一种实现方法，如果需要用于实际项目中，请务必进行全面的测试和评估，并采取适当的安全措施。