2013 Hash file research con't'd

[thefiremind]

I would try to play around with the file, too, but I can't seem to make a (C++) program that computes and outputs the hash according to this algorithm... I think I'm using signed types that should be unsigned, or vice versa. Can someone share a piece of code that I can reuse?

[pcastellazzi]

I would try to play around with the file, too, but I can't seem to make a (C++) program that computes and outputs the hash according to this algorithm... I think I'm using signed types that should be unsigned, or vice versa. Can someone share a piece of code that I can reuse?

Remember to force 32 bits data types. If you are using a 64 bit compiler the size of the integer will be different and the output too, due to overflows not happend when expected.

[RiiakShiNal]

I would try to play around with the file, too, but I can't seem to make a (C++) program that computes and outputs the hash according to this algorithm... I think I'm using signed types that should be unsigned, or vice versa. Can someone share a piece of code that I can reuse?

Here is the code I'm using in C# (though it should convert to C++ fairly easily):

Code: Select all

      private UInt32 MtG2013Hash(byte[] abytData)
      {
         UInt32 nHash = 0x811C9DC5;
         for (int i = 0; i < 0x10C4; i++)
         {
            nHash *= 0x1000193;
            nHash ^= abytData[i];
         }
         return nHash;
      }


I have not yet had the code error out due to overflow, but then again I also have not yet done much testing (but I have verified it works and produces the desired result several times).

Remember to force 32 bits data types. If you are using a 64 bit compiler the size of the integer will be different and the output too, due to overflows not happend when expected.

I specifically use UInt32 for this very reason (my development machine is 64-bit).

[thefiremind]

I finally made it, but the result is reversed if I compare it to hash.file contents: I get
78 9b 01 10
while hash.file contains
10 01 9b 78
Is it normal (hash.file intentionally stores the hash reversed) or am I doing something stupid?

This is my C++ code (updated), if someone is interested:

Code: Select all

#include <iostream>
#include <fstream>

using namespace std;

int main(int argc, char* argv[])
{
   if (argc < 2) // no file specified
   {
      cout << "Usage: D13Hash filename" << endl;
      return 1;
   }

   // read file
   ifstream fl(argv[1], ios_base::in | ios_base::binary | ios_base::ate);
   size_t len = fl.tellg();
   unsigned char *bytes = new unsigned char[len];
   fl.seekg(0, ios::beg);
   fl.read(bytes, len);
   fl.close();

   // compute hash
   unsigned int hash = 0x811C9DC5;
   for (int i=0; i < 0x10C4; i++)
   {
      hash *= 0x1000193;
      hash ^= bytes[i];
   }

   // free memory
   delete bytes;

   // save output in correct order
   unsigned char result[4];
   result[0] = (hash & 0xFF);
   result[1] = ((hash & 0xFF00) >> 8);
   result[2] = ((hash & 0xFF0000) >> 16);
   result[3] = ((hash & 0xFF000000) >> 24);

   // write output
   cout.flags(ios::hex);
   cout << "Length: 0x" << len << endl;
   cout << "Hash: 0x";
   for (int i=0; i<4; i++)
   {
      unsigned int output = (unsigned int)result[i];
      if (output < 16)
         cout << "0";
      cout << output;
   }
   cout << endl;

   // let the user read the result
   cout << "Press any key to end..." << endl;
   getchar();

   return 0;
}

(I'm using a 32-bit compiler so I have no need to specify it on the int type)

[RiiakShiNal]

I finally made it, but the result is reversed if I compare it to hash.file contents: I get
78 9b 01 10
while hash.file contains
10 01 9b 78
Is it normal (hash.file intentionally stores the hash reversed) or am I doing something stupid?

This is normal due to string conversions versus how things are saved.

The reason it is displaying backward for you is because you are converting it to a raw/Motorola hex string (the most significant byte is first) when writing an integer out to a file (as an integer) it is usually stored as least significant byte first (when looking at the hex this is the Intel hex display).

If you want to convert the hash to a hex string you need to take this into account like so:

Code: Select all

cout << "Hash: 0x" << (unsigned char)(hash & 0xff);
cout << (unsigned char)((hash & 0xff00) >> 8);
cout << (unsigned char)((hash & 0xff0000) >> 16);
cout << (unsigned char)((hash & 0xff000000) >> 24) << endl;

[thefiremind]

Thanks, that's exactly what I needed! I updated the code, now it displays the hash in the correct order and the program could be expanded so that it writes the hash to a file (from the "result" variable).

By the way, I think I got the right procedure yesterday, too, but without realizing that the hash was just reversed.

EDIT: I made something more complete here if someone wants to mess around with the profile without making a program of his own.

[spirolone]

I know that this is an old thread, but creating hash.file is still usefull. Even if thefiremind program is perfect, I wanted to do the same in vba code, cause I wanted an automatized procedure. I came across some problems cause there are no unsigned integer variables of 4 byte, so you can use only 31 bits and you will get a lot of overflow errors. This is my code that resolve the issue splitting 4 bytes number into two. Maybe someone can find something usefull:

Code: Select all

    'Calculating hash.file
    Dim hashL As Long       'Two Least Significant Bytes
    Dim hashH As Long       'Two Most Significant Bytes

    hashL = 40389           ' 9DC5
    hashH = 33052           ' 811C
    For i = 0 To UBound(fileContent)
        hashH = hashH * 403
        hashH = hashH + (hashL * 256)
        hashL = hashL * 403
        hashH = hashH + ((hashL And &HFFF0000) / &H10000)
        hashH = hashH And &H1000FFFF
        hashL = hashL And &H1000FFFF
        hashL = hashL Xor fileContent(i)
    Next i

    'Writing hash.file
    fileNumber = FreeFile()
    Open (filePath + "hash.file") For Binary As fileNumber
    Put fileNumber, , CByte(hashL And &H100FF)
    Put fileNumber, , CByte((hashL And &H1FF00) / &H100)
    Put fileNumber, , CByte(hashH And &H100FF)
    Put fileNumber, , CByte((hashH And &H1FF00) / &H100)
    Close fileNumber