用c 获取文件MD5值的实现方法

 更新时间:2013年05月27日 16:13:44   作者:  
本篇文章是对用c语言获取文件MD5值的方法进行了详细的分析介绍,需要的朋友参考下
网上有 md5.c , md5.h, 但是里面只有 MD5Init(), MD5Update(), MD5Final() 三个函数,
只可以直接对字符进行操作, 而没有直接求文件md5的接口. 以下是我的实现, 可计算32位和16位的md5值.
复制代码 代码如下:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "md5.h"
char *MD5_file (char *path, int md5_len)
{
 FILE *fp = fopen (path, "rb");
 MD5_CTX mdContext;
 int bytes;
 unsigned char data[1024];
 char *file_md5;
 int i;
 if (fp == NULL) {
  fprintf (stderr, "fopen %s failed\n", path);
  return NULL;
 }
 MD5Init (&mdContext);
 while ((bytes = fread (data, 1, 1024, fp)) != 0)
 {
  MD5Update (&mdContext, data, bytes);
 }
 MD5Final (&mdContext);

 file_md5 = (char *)malloc((md5_len + 1) * sizeof(char));
 if(file_md5 == NULL)
 {
  fprintf(stderr, "malloc failed.\n");
  return NULL;
 }
 memset(file_md5, 0, (md5_len + 1));

 if(md5_len == 16)
 {
  for(i=4; i<12; i++)
  {
   sprintf(&file_md5[(i-4)*2], "%02x", mdContext.digest[i]);
  }
 }
 else if(md5_len == 32)
 {
  for(i=0; i<16; i++)
  {
   sprintf(&file_md5[i*2], "%02x", mdContext.digest[i]);
  }
 }
 else
 {
  fclose(fp);
  free(file_md5);
  return NULL;
 }

 fclose (fp);
 return file_md5;
}
int main(int argc, char *argv[])
{
 char *md5;

 md5 = MD5_file("temp", 16);
 printf("16: %s\n", md5);
 free(md5);

 md5 = MD5_file("temp", 32);
 printf("32: %s\n", md5);
 free(md5);
 return 0;
}

以下是 md5.c的源码
复制代码 代码如下:

#include "md5.h"
/*
 **********************************************************************
 ** md5.c                                                            **
 ** RSA Data Security, Inc. MD5 Message Digest Algorithm             **
 ** Created: 2/17/90 RLR                                             **
 ** Revised: 1/91 SRD,AJ,BSK,JT Reference C Version                  **
 **********************************************************************
 */
/*
 **********************************************************************
 ** Copyright (C) 1990, RSA Data Security, Inc. All rights reserved. **
 **                                                                  **
 ** License to copy and use this software is granted provided that   **
 ** it is identified as the "RSA Data Security, Inc. MD5 Message     **
 ** Digest Algorithm" in all material mentioning or referencing this **
 ** software or this function.                                       **
 **                                                                  **
 ** License is also granted to make and use derivative works         **
 ** provided that such works are identified as "derived from the RSA **
 ** Data Security, Inc. MD5 Message Digest Algorithm" in all         **
 ** material mentioning or referencing the derived work.             **
 **                                                                  **
 ** RSA Data Security, Inc. makes no representations concerning      **
 ** either the merchantability of this software or the suitability   **
 ** of this software for any particular purpose.  It is provided "as **
 ** is" without express or implied warranty of any kind.             **
 **                                                                  **
 ** These notices must be retained in any copies of any part of this **
 ** documentation and/or software.                                   **
 **********************************************************************
 */
/* -- include the following line if the md5.h header file is separate -- */
/* #include "md5.h" */
/* forward declaration */
static void Transform ();
static unsigned char PADDING[64] = {
  0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};
/* F, G and H are basic MD5 functions: selection, majority, parity */
#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)))
/* ROTATE_LEFT rotates x left n bits */
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4 */
/* Rotation is separate from addition to prevent recomputation */
#define FF(a, b, c, d, x, s, ac) \
  {(a) += F ((b), (c), (d)) + (x) + (UINT4)(ac); \
   (a) = ROTATE_LEFT ((a), (s)); \
   (a) += (b); \
  }
#define GG(a, b, c, d, x, s, ac) \
  {(a) += G ((b), (c), (d)) + (x) + (UINT4)(ac); \
   (a) = ROTATE_LEFT ((a), (s)); \
   (a) += (b); \
  }
#define HH(a, b, c, d, x, s, ac) \
  {(a) += H ((b), (c), (d)) + (x) + (UINT4)(ac); \
   (a) = ROTATE_LEFT ((a), (s)); \
   (a) += (b); \
  }
#define II(a, b, c, d, x, s, ac) \
  {(a) += I ((b), (c), (d)) + (x) + (UINT4)(ac); \
   (a) = ROTATE_LEFT ((a), (s)); \
   (a) += (b); \
  }
void MD5Init (MD5_CTX *mdContext)
{
  mdContext->i[0] = mdContext->i[1] = (UINT4)0;
  /* Load magic initialization constants.
   */
  mdContext->buf[0] = (UINT4)0x67452301;
  mdContext->buf[1] = (UINT4)0xefcdab89;
  mdContext->buf[2] = (UINT4)0x98badcfe;
  mdContext->buf[3] = (UINT4)0x10325476;
}
void MD5Update (MD5_CTX *mdContext, unsigned char *inBuf, unsigned int inLen)
{
  UINT4 in[16];
  int mdi;
  unsigned int i, ii;
  /* compute number of bytes mod 64 */
  mdi = (int)((mdContext->i[0] >> 3) & 0x3F);
  /* update number of bits */
  if ((mdContext->i[0] + ((UINT4)inLen << 3)) < mdContext->i[0])
    mdContext->i[1]++;
  mdContext->i[0] += ((UINT4)inLen << 3);
  mdContext->i[1] += ((UINT4)inLen >> 29);
  while (inLen--) {
    /* add new character to buffer, increment mdi */
    mdContext->in[mdi++] = *inBuf++;
    /* transform if necessary */
    if (mdi == 0x40) {
      for (i = 0, ii = 0; i < 16; i++, ii += 4)
        in[i] = (((UINT4)mdContext->in[ii+3]) << 24) |
                (((UINT4)mdContext->in[ii+2]) << 16) |
                (((UINT4)mdContext->in[ii+1]) << 8) |
                ((UINT4)mdContext->in[ii]);
      Transform (mdContext->buf, in);
      mdi = 0;
    }
  }
}
void MD5Final (MD5_CTX *mdContext)
{
  UINT4 in[16];
  int mdi;
  unsigned int i, ii;
  unsigned int padLen;
  /* save number of bits */
  in[14] = mdContext->i[0];
  in[15] = mdContext->i[1];
  /* compute number of bytes mod 64 */
  mdi = (int)((mdContext->i[0] >> 3) & 0x3F);
  /* pad out to 56 mod 64 */
  padLen = (mdi < 56) ? (56 - mdi) : (120 - mdi);
  MD5Update (mdContext, PADDING, padLen);
  /* append length in bits and transform */
  for (i = 0, ii = 0; i < 14; i++, ii += 4)
    in[i] = (((UINT4)mdContext->in[ii+3]) << 24) |
            (((UINT4)mdContext->in[ii+2]) << 16) |
            (((UINT4)mdContext->in[ii+1]) << 8) |
            ((UINT4)mdContext->in[ii]);
  Transform (mdContext->buf, in);
  /* store buffer in digest */
  for (i = 0, ii = 0; i < 4; i++, ii += 4) {
    mdContext->digest[ii] = (unsigned char)(mdContext->buf[i] & 0xFF);
    mdContext->digest[ii+1] =
      (unsigned char)((mdContext->buf[i] >> 8) & 0xFF);
    mdContext->digest[ii+2] =
      (unsigned char)((mdContext->buf[i] >> 16) & 0xFF);
    mdContext->digest[ii+3] =
      (unsigned char)((mdContext->buf[i] >> 24) & 0xFF);
  }
}
/* Basic MD5 step. Transform buf based on in.
 */
static void Transform (UINT4 *buf, UINT4 *in)
{
  UINT4 a = buf[0], b = buf[1], c = buf[2], d = buf[3];
  /* Round 1 */
#define S11 7
#define S12 12
#define S13 17
#define S14 22
  FF ( a, b, c, d, in[ 0], S11, 3614090360); /* 1 */
  FF ( d, a, b, c, in[ 1], S12, 3905402710); /* 2 */
  FF ( c, d, a, b, in[ 2], S13,  606105819); /* 3 */
  FF ( b, c, d, a, in[ 3], S14, 3250441966); /* 4 */
  FF ( a, b, c, d, in[ 4], S11, 4118548399); /* 5 */
  FF ( d, a, b, c, in[ 5], S12, 1200080426); /* 6 */
  FF ( c, d, a, b, in[ 6], S13, 2821735955); /* 7 */
  FF ( b, c, d, a, in[ 7], S14, 4249261313); /* 8 */
  FF ( a, b, c, d, in[ 8], S11, 1770035416); /* 9 */
  FF ( d, a, b, c, in[ 9], S12, 2336552879); /* 10 */
  FF ( c, d, a, b, in[10], S13, 4294925233); /* 11 */
  FF ( b, c, d, a, in[11], S14, 2304563134); /* 12 */
  FF ( a, b, c, d, in[12], S11, 1804603682); /* 13 */
  FF ( d, a, b, c, in[13], S12, 4254626195); /* 14 */
  FF ( c, d, a, b, in[14], S13, 2792965006); /* 15 */
  FF ( b, c, d, a, in[15], S14, 1236535329); /* 16 */
  /* Round 2 */
#define S21 5
#define S22 9
#define S23 14
#define S24 20
  GG ( a, b, c, d, in[ 1], S21, 4129170786); /* 17 */
  GG ( d, a, b, c, in[ 6], S22, 3225465664); /* 18 */
  GG ( c, d, a, b, in[11], S23,  643717713); /* 19 */
  GG ( b, c, d, a, in[ 0], S24, 3921069994); /* 20 */
  GG ( a, b, c, d, in[ 5], S21, 3593408605); /* 21 */
  GG ( d, a, b, c, in[10], S22,   38016083); /* 22 */
  GG ( c, d, a, b, in[15], S23, 3634488961); /* 23 */
  GG ( b, c, d, a, in[ 4], S24, 3889429448); /* 24 */
  GG ( a, b, c, d, in[ 9], S21,  568446438); /* 25 */
  GG ( d, a, b, c, in[14], S22, 3275163606); /* 26 */
  GG ( c, d, a, b, in[ 3], S23, 4107603335); /* 27 */
  GG ( b, c, d, a, in[ 8], S24, 1163531501); /* 28 */
  GG ( a, b, c, d, in[13], S21, 2850285829); /* 29 */
  GG ( d, a, b, c, in[ 2], S22, 4243563512); /* 30 */
  GG ( c, d, a, b, in[ 7], S23, 1735328473); /* 31 */
  GG ( b, c, d, a, in[12], S24, 2368359562); /* 32 */
  /* Round 3 */
#define S31 4
#define S32 11
#define S33 16
#define S34 23
  HH ( a, b, c, d, in[ 5], S31, 4294588738); /* 33 */
  HH ( d, a, b, c, in[ 8], S32, 2272392833); /* 34 */
  HH ( c, d, a, b, in[11], S33, 1839030562); /* 35 */
  HH ( b, c, d, a, in[14], S34, 4259657740); /* 36 */
  HH ( a, b, c, d, in[ 1], S31, 2763975236); /* 37 */
  HH ( d, a, b, c, in[ 4], S32, 1272893353); /* 38 */
  HH ( c, d, a, b, in[ 7], S33, 4139469664); /* 39 */
  HH ( b, c, d, a, in[10], S34, 3200236656); /* 40 */
  HH ( a, b, c, d, in[13], S31,  681279174); /* 41 */
  HH ( d, a, b, c, in[ 0], S32, 3936430074); /* 42 */
  HH ( c, d, a, b, in[ 3], S33, 3572445317); /* 43 */
  HH ( b, c, d, a, in[ 6], S34,   76029189); /* 44 */
  HH ( a, b, c, d, in[ 9], S31, 3654602809); /* 45 */
  HH ( d, a, b, c, in[12], S32, 3873151461); /* 46 */
  HH ( c, d, a, b, in[15], S33,  530742520); /* 47 */
  HH ( b, c, d, a, in[ 2], S34, 3299628645); /* 48 */
  /* Round 4 */
#define S41 6
#define S42 10
#define S43 15
#define S44 21
  II ( a, b, c, d, in[ 0], S41, 4096336452); /* 49 */
  II ( d, a, b, c, in[ 7], S42, 1126891415); /* 50 */
  II ( c, d, a, b, in[14], S43, 2878612391); /* 51 */
  II ( b, c, d, a, in[ 5], S44, 4237533241); /* 52 */
  II ( a, b, c, d, in[12], S41, 1700485571); /* 53 */
  II ( d, a, b, c, in[ 3], S42, 2399980690); /* 54 */
  II ( c, d, a, b, in[10], S43, 4293915773); /* 55 */
  II ( b, c, d, a, in[ 1], S44, 2240044497); /* 56 */
  II ( a, b, c, d, in[ 8], S41, 1873313359); /* 57 */
  II ( d, a, b, c, in[15], S42, 4264355552); /* 58 */
  II ( c, d, a, b, in[ 6], S43, 2734768916); /* 59 */
  II ( b, c, d, a, in[13], S44, 1309151649); /* 60 */
  II ( a, b, c, d, in[ 4], S41, 4149444226); /* 61 */
  II ( d, a, b, c, in[11], S42, 3174756917); /* 62 */
  II ( c, d, a, b, in[ 2], S43,  718787259); /* 63 */
  II ( b, c, d, a, in[ 9], S44, 3951481745); /* 64 */
  buf[0] += a;
  buf[1] += b;
  buf[2] += c;
  buf[3] += d;
}
/*
 **********************************************************************
 ** End of md5.c                                                     **
 ******************************* (cut) ********************************
 */

以下是 md5.h 的源码
复制代码 代码如下:

/*
 **********************************************************************
 ** md5.h -- Header file for implementation of MD5                   **
 ** RSA Data Security, Inc. MD5 Message Digest Algorithm             **
 ** Created: 2/17/90 RLR                                             **
 ** Revised: 12/27/90 SRD,AJ,BSK,JT Reference C version              **
 ** Revised (for MD5): RLR 4/27/91                                   **
 **   -- G modified to have y&~z instead of y&z                      **
 **   -- FF, GG, HH modified to add in last register done            **
 **   -- Access pattern: round 2 works mod 5, round 3 works mod 3    **
 **   -- distinct additive constant for each step                    **
 **   -- round 4 added, working mod 7                                **
 **********************************************************************
 */
/*
 **********************************************************************
 ** Copyright (C) 1990, RSA Data Security, Inc. All rights reserved. **
 **                                                                  **
 ** License to copy and use this software is granted provided that   **
 ** it is identified as the "RSA Data Security, Inc. MD5 Message     **
 ** Digest Algorithm" in all material mentioning or referencing this **
 ** software or this function.                                       **
 **                                                                  **
 ** License is also granted to make and use derivative works         **
 ** provided that such works are identified as "derived from the RSA **
 ** Data Security, Inc. MD5 Message Digest Algorithm" in all         **
 ** material mentioning or referencing the derived work.             **
 **                                                                  **
 ** RSA Data Security, Inc. makes no representations concerning      **
 ** either the merchantability of this software or the suitability   **
 ** of this software for any particular purpose.  It is provided "as **
 ** is" without express or implied warranty of any kind.             **
 **                                                                  **
 ** These notices must be retained in any copies of any part of this **
 ** documentation and/or software.                                   **
 **********************************************************************
 */
/* typedef a 32 bit type */
typedef unsigned long int UINT4;
/* Data structure for MD5 (Message Digest) computation */
typedef struct {
  UINT4 i[2];                   /* number of _bits_ handled mod 2^64 */
  UINT4 buf[4];                                    /* scratch buffer */
  unsigned char in[64];                              /* input buffer */
  unsigned char digest[16];     /* actual digest after MD5Final call */
} MD5_CTX;
void MD5Init ();
void MD5Update ();
void MD5Final ();
/*
 **********************************************************************
 ** End of md5.h                                                     **
 ******************************* (cut) ********************************
 */

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