在C中返回错误的MD5哈希 [英] Returning wrong MD5 hash in C

问题描述

我正在尝试使用原始/未修改的md5.h和 http://www.arp.harvard.edu .但是我的结果不同于我测试过的所有md5在线工具.此代码有什么问题?谢谢.

I am trying to generate MD5 hash for an string "Hello World" using the original/untouched md5.h and md5c.c from http://www.arp.harvard.edu. But my result differs from all md5 online tools i have tested. Whats wrong this this code? Thank you.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "md5.h"

void MD5hash(unsigned char *data, unsigned int dataLen, unsigned char *digest) {
    MD5_CTX c;
    MD5Init(&c);
    MD5Update(&c, data, dataLen);
    MD5Final(digest, &c);
}

int main(int argc, const char * argv[]) {
    unsigned char digest[16];
    const char *s = "Hello World";
    unsigned int l = (unsigned int)strlen(s);

    MD5hash((unsigned char *)s, l, digest);
    for(int i = 0; i < 16; ++i)
         printf("%02x", digest[i]);
    return 0;
}

// My result: f2877a72c40494318c4b050bb436c582
// But online tools output: b10a8db164e0754105b7a99be72e3fe5

推荐答案

您对填充有疑问. MD5哈希算法适用于512位块.当您的最终块少于512位时，需要对其进行填充.在您的示例中，第一个块也是最后一个块，因为它少于512位.

You have an issue with padding. The MD5 Hash algorithm works on 512-bit blocks. When your final block is less than 512 bits, it needs to be padded. In your example, the first block is also the last block because it's less than 512 bits.

填充的格式称为 Merkle–Damgård构造.

您可以在此处找到一些伪代码.

You can find some pseudo code that includes padding here.

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