In C++, How to get MD5 hash of a file?

Question

I've the file path. How can I get the MD5 hash of it?

Thanks

Answer 1

See this code sample, too much code to paste here:

Sample

Answer 2

You can implement the md5 algorithm yourself (examples are all over the web), or you can link against the openssl libs and use openssl's digest functions. here's an example to get the md5 of a bytearray :

#include <openssl/md5.h>
QByteArray AESWrapper::md5 ( const QByteArray& data) {
unsigned char * tmp_hash;
tmp_hash = MD5((const unsigned char*)data.constData(), data.length(), NULL);
return QByteArray((const char*)tmp_hash, MD5_DIGEST_LENGTH);
}

Answer 3

Google gives, among many others, this

Answer 4

Here's a straight forward implementation of the md5sum command that computes and displays the MD5 of the file specified on the command-line. It needs to be linked against the openssl library (gcc md5.c -o md5 -lssl) to work. It's pure C, but you should be able to adapt it to your C++ application easily enough.

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <openssl/md5.h>

unsigned char result[MD5_DIGEST_LENGTH];

// Print the MD5 sum as hex-digits.
void print_md5_sum(unsigned char* md) {
    int i;
    for(i=0; i <MD5_DIGEST_LENGTH; i++) {
            printf("%02x",md[i]);
    }
}

// Get the size of the file by its file descriptor
unsigned long get_size_by_fd(int fd) {
    struct stat statbuf;
    if(fstat(fd, &statbuf) < 0) exit(-1);
    return statbuf.st_size;
}

int main(int argc, char *argv[]) {
    int file_descript;
    unsigned long file_size;
    char* file_buffer;

    if(argc != 2) { 
         printf("Must specify the file\n");
         exit(-1);
    }
    printf("using file:\t%s\n", argv[1]);

    file_descript = open(argv[1], O_RDONLY);
    if(file_descript < 0) exit(-1);

    file_size = get_size_by_fd(file_descript);
    printf("file size:\t%lu\n", file_size);

    file_buffer = mmap(0, file_size, PROT_READ, MAP_SHARED, file_descript, 0);
    MD5((unsigned char*) file_buffer, file_size, result);

    print_md5_sum(result);
    printf("  %s\n", argv[1]);

    return 0;
}

Answer 5

I have used botan to perform this operation and others before. AraK has pointed out Crypto++. I guess both libraries are perfectly valid. Now it is up to you :-).

Answer 6

If anybody still in interest, where are pretty library at http://256.com/sources/md5/ with expample of use. This is the simplest lib for md5

Answer 7

If you have a copy of Applied Cryptography, you can copy the MD5 code from the back :)

Answer 8

Using Crypto++, you could do the following:

#include <sha.h>
#include <iostream> 

SHA256 sha; 
while ( !f.eof() ) { 
   char buff[4096];
   int numchars = f.read(...); 
   sha.Update(buff, numchars); 
}
char hash[size]; 
sha.Final(hash); 
cout << hash <<endl; 

I have a need for something very similar, because I can't read in multi-gigabyte files just to compute a hash. In theory I could memory map them, but I have to support 32bit platforms - that's still problematic for large files.

Answer 9

Check this out: http://www.zedwood.com/article/121/cpp-md5-function It answers your question

Answer 10

There is a collection of implementations in C, C++ and many other languages here.

I put up an implementation here.