Change the MD5 of a file.

#include <windows.h> //for ZeroMemory macro
#include <fstream> //derp obvious.
#include <time.h>

int quit(char* msg)
{
	printf(msg); //print the message to the console window
	return -1; //-1 is my signifier that the function failed.
}

char* ReadFromStream(std::fstream *baseStream, int offset, int dwSize)
{
	char* ret = new char[dwSize]; //create a buffer
	ZeroMemory(ret, sizeof(ret)); //zero the memory like a mad dawg
	baseStream->seekg(offset, std::ios::beg); //seek to the offset from the beginning of the stream
	baseStream->read(ret, dwSize); //read dwSize bytes from the stream into the buffer
	return ret; //return the buffer
}

char* intToBytes(int val)
{
	/**** not really my function, cbf learning bitshifting ***/
	char* ret = new char[4];
	ret[0] = (val >> 24) & 0xFF;
	ret[1] = (val >> 16) & 0xFF;
	ret[2] = (val >> 8) & 0xFF;
	ret[3] = val & 0xFF;
	return ret;
}

int ChangeMD5(char* file)
{
	using std::ios; //im too lazy to do more than one :: 
	
	//create the random int.
	srand(time(NULL) * time(NULL)); //seed the random, dont have to be too fancy
	int rnd = rand(); //generate a pseudo-random
	char *newMd5 = intToBytes(rnd); //convert our random to bytes.

	std::fstream PEStream (file, ios::binary | ios::in | ios::out); //open a stream to the file.

	char *buff = ReadFromStream(&PEStream, 0, 2); //read the start signature (MUST BE 'MZ' FOR ALL PE)
	if ( strcmp(buff, "MZ") != 0 ) { return quit("Not a valid PE File"); } //not a PE, exit with a message.

	buff = ReadFromStream(&PEStream, 0x3C, 4); //read 4 bytes from the stream.
	int lfanew = *reinterpret_cast<signed*>( buff ); //cast the char to a signed int

	buff = ReadFromStream(&PEStream, lfanew, 4); //read the PE signature from the stream
	if ( strcmp(buff, "PE\0\0") != 0 ) { return quit("Not a valid PE File"); } //PE files all have the signature PE followed by 2 null bytes.
	
	/** OKAY WE'VE VERIFIED IT'S A PE, NOW IT'S SAFE TO WRITE **/

	PEStream.seekp(0x1C, ios::beg); //seek to the start of the reserved space	
	PEStream.write(newMd5, 4); //write those bytes to the file in the reserved space
	
	PEStream.flush(); //flush all waiting shit.
	PEStream.close(); //close the stream
	return 0; //success
}

void main()
{
	if ( ChangeMD5("C:\\test.exe") == 0)
		MessageBoxA(NULL, "OMG FUCK YEAH", "MD5 Changed", 0); 
}