如何在C中创建字符串的md5哈希？

Question

我发现了一些由以下原型组成的md5代码......

我一直在试图找出我要放置我想要哈希的字符串的位置,我需要调用哪些函数,以及在经过哈希处理后找到字符串的位置.我对uint32 buf [4]和uint32位[2]在结构中的含义感到困惑.

struct MD5Context {
    uint32 buf[4];
    uint32 bits[2];
    unsigned char in[64];
};

/*
 * Start MD5 accumulation.  Set bit count to 0 and buffer to mysterious
 * initialization constants.
 */
void MD5Init(struct MD5Context *context);

/*
 * Update context to reflect the concatenation of another buffer full
 * of bytes.
 */
void MD5Update(struct MD5Context *context, unsigned char const *buf, unsigned len);

/*
 * Final wrapup - pad to 64-byte boundary with the bit pattern 
 * 1 0* (64-bit count of bits processed, MSB-first)
 */
void MD5Final(unsigned char digest[16], struct MD5Context *context);

/*
 * The core of the MD5 algorithm, this alters an existing MD5 hash to
 * reflect the addition of 16 longwords of new data.  MD5Update blocks
 * the data and converts bytes into longwords for this routine.
 */
void MD5Transform(uint32 buf[4], uint32 const in[16]);

Answer 1

我不知道这个特殊的库,但我使用了非常类似的调用.所以这是我最好的猜测:

unsigned char digest[16];
const char* string = "Hello World";
struct MD5Context context;
MD5Init(&context);
MD5Update(&context, string, strlen(string));
MD5Final(digest, &context);

这将返回哈希的整数表示.如果要将其作为字符串传递,则可以将其转换为十六进制表示形式.

char md5string[33];
for(int i = 0; i < 16; ++i)
    sprintf(&md5string[i*2], "%02x", (unsigned int)digest[i]);

Answer 2

这是一个完整的例子:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#if defined(__APPLE__)
#  define COMMON_DIGEST_FOR_OPENSSL
#  include <CommonCrypto/CommonDigest.h>
#  define SHA1 CC_SHA1
#else
#  include <openssl/md5.h>
#endif

char *str2md5(const char *str, int length) {
    int n;
    MD5_CTX c;
    unsigned char digest[16];
    char *out = (char*)malloc(33);

    MD5_Init(&c);

    while (length > 0) {
        if (length > 512) {
            MD5_Update(&c, str, 512);
        } else {
            MD5_Update(&c, str, length);
        }
        length -= 512;
        str += 512;
    }

    MD5_Final(digest, &c);

    for (n = 0; n < 16; ++n) {
        snprintf(&(out[n*2]), 16*2, "%02x", (unsigned int)digest[n]);
    }

    return out;
}

    int main(int argc, char **argv) {
        char *output = str2md5("hello", strlen("hello"));
        printf("%s\n", output);
        free(output);
        return 0;
    }

Answer 3

正如其他答案所提到的,以下调用将计算哈希值:

MD5Context md5;
MD5Init(&md5);
MD5Update(&md5, data, datalen);
MD5Final(digest, &md5);

将其拆分为许多函数的目的是让您流式传输大型数据集.

例如,如果你正在对一个10GB的文件进行哈希处理并且它不适合ram,那么你可以这样做.您将以较小的块读取文件并调用MD5Update它们.

MD5Context md5;
MD5Init(&md5);

fread(/* Read a block into data. */)
MD5Update(&md5, data, datalen);

fread(/* Read the next block into data. */)
MD5Update(&md5, data, datalen);

fread(/* Read the next block into data. */)
MD5Update(&md5, data, datalen);

...

//  Now finish to get the final hash value.
MD5Final(digest, &md5);

Answer 4

说实话,原型附带的评论似乎很清楚.像这样的东西应该做的伎俩:

void compute_md5(char *str, unsigned char digest[16]) {
    MD5Context ctx;
    MD5Init(&ctx);
    MD5Update(&ctx, str, strlen(str));
    MD5Final(digest, &ctx);
}

str你想要哈希的C字符串在哪里,并且digest是得到的MD5摘要.