MD5 checksum for file

[narjunkumar]

Hi..

I would like to get MD5 checksums of files in my program for verification purposes.. and I would
like to use a very simple function.. like..

bool generateMD5_for_file(FILE * fp, std::string generatedchecksum) ;

Could anyone direct me to some appropriate wrapper routine which does this..

Thanks!!

[VictorN]

Did you check it out: http://www.google.com/search?sourcei...cksums+windows
Or what exactly is your problem?

[narjunkumar]

@Victor..

Lets say.. I have a table.. that has filepaths and their corresponding MD5 checksums..
I want to programatically open each file, compute the MD5 checksum for it... and then verify whether the MD5 thats given in the table is the right one or not.

So i just need a library or something.. where I can just supply the file path, or file pointer.. and then get the MD5 string for the file..

Thanks.!!!

[hoxsiew]

Something like this:

#include <wincrypt.h>

int CalcHash(FILE *f,char *md5sum)
{
  HCRYPTPROV hProv;
  HCRYPTHASH hHash;
  unsigned char buf[1024];
  unsigned char hsh[16];
  unsigned long sz;
  char byt[3];
  int rc,err,i;
  size_t fsz;

  rc=CryptAcquireContext(&hProv,NULL,MS_STRONG_PROV,PROV_RSA_FULL,0);
  if(!rc){
    err=GetLastError();
    if(err==0x80090016){
      //first time using crypto API, need to create a new keyset
      rc=CryptAcquireContext(&hProv,NULL,MS_STRONG_PROV,PROV_RSA_FULL,CRYPT_NEWKEYSET);
      if(!rc){
        err=GetLastError();
        return 0;
      }
    }
  }

  CryptCreateHash(hProv,CALG_MD5,0,0,&hHash);
  while((fsz=fread(buf,1,1024,f))!=0){
    CryptHashData(hHash,(unsigned char *)buf,fsz,0);
  }
  sz=16;
  CryptGetHashParam(hHash,HP_HASHVAL,hsh,&sz,0);
  md5sum[0]=0;
  for(i=0;i<sz;i++){
    sprintf(byt,"%.2X",hsh[i]);
    strcat(md5sum,byt);
  }
  CryptDestroyHash(hHash);
  CryptReleaseContext(hProv,0);
  return 1;
}


int main()
{
  FILE *f;
  char md5sum[17];

  f=fopen("c:/test.bmp","rb");
  CalcHash(f,md5sum);
  fclose(f);
  return 0;
}

[narjunkumar]

Thanks.. that was exactly what i was looking for..

[Larry Leonard]

This fixes a crash on the fclose() call: The variable "md5sum" should be 33 bytes, not 17:

char md5sum[(16 * 2) + 1] = { 0 };

... because "sz" is set to 16, and the sprintf is writing two characters at a time, up to "sz".