trouble with random string generator

whatsinthename (2)
I am trying to code a random string generator using boost libraries for random number generation. I have tried coding the same keygen without using boost and relying on normal PRNG with a time seed.

here is the code: 

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// keygen.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <ctime>
#include <string>

#include <boost/random/mersenne_twister.hpp>
#include <boost/random/uniform_int.hpp>
#include <boost/random/variate_generator.hpp>

#include "md5wrapper.h"
using namespace std;
using namespace boost;


int _tmain(int argc, _TCHAR* argv[])
{
	//Define keyspace
	//string alpha="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
	string alpha="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	//Setup random number generator
	static mt19937 generator(static_cast<unsigned int>(std::time(0)));
	uniform_int<> uni_int_dist( 0, alpha.length() );
	variate_generator< mt19937&, uniform_int<> > r( generator, uni_int_dist );
	
	//hash init
	md5wrapper md5;
		
	//initialize keygen
	
	int n = 10; // key length
	int count = 0;
	
	//timing
	clock_t start,finish;
	double time;
	start = clock();

	while (1) {
		//generate key
		char *key = new char[n+1];
		for(int i=0;i<n;i++) 
			key[i] = alpha[r()];
		key[n] = '\0';
		//generate md5 hash
		string hash = md5.getHashFromString(md5.getHashFromString(string(key,n)));
		//output status
		if(((count++)%10000) ==0 )
		{
			time = (double(clock())-double(start))/CLOCKS_PER_SEC;
			cout<<count<<'\t'<<time<<'\t'<<key<<'\t'<<hash<<endl;
		}
		//look for a target hash
		if (hash=="2c4972c770836eaf3b237a561b06daaa") 
		{
			cout<<key<<'\t'<<hash<<'\n';
			getchar();
		}
		delete [] key;
	}
	

	return 0;
}


As per the code it should generate random strings of size n, and compute its md5 hashes. However, when running the code, it sometimes generates smaller strings or even empty strings. I do not understand why that is happening..

Any help/tips appreciated with the code. Thanx
firedraco (6247)
I might be misinterpreting what you are trying to do, but couldn't you just generate a random number between 0 and 25, then get a particular character from the vector of characters, and push_back it into the string?
whatsinthename (2)
its the same thing essentially, i have tried using string.push_back(). Still it is generating strings of smaller sizes sometimes.
firedraco (6247)
It was something like this, right? :

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while(String.size() < 25) {
   char temp = rand_int('a','z'); //get a random char from a - z into temp (no this function doesn't exist normally)
   String.push_back(temp);
}


EDIT: actually, i meant 'z', but...

Last edited on
Mal Reynolds (111)
if you are worried about string size, i would suggest using firedraco's code above, and just replacing the '25' in the while statement with a random number between your string size's min/max.
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