Thread: How to create a string of alphanumeric values???

Do you mean you want to generate a random string?

I'm not at home right now. When I get there, I will send you an example of a program I made which generated a random word. That program generated a random word and used some letters more than the others. Thats why I used a char string, where it chooses a letter from:

Code:

char letters[]={"aaabccdeefghhiiijkkkll"};

And so on. If there's more of one letter, it appears more often.
I think your program can be made quite easily, because you can just use ASCII character values.
Once I get home I will post some examples.

Code:

srand( time(0) );

// letters_numbers is a string type which has all the small and capital letters, with numbers too
string letters_numbers = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

// This is where the 'random' string is stored
string RandomString = "";

for ( loop for whatever amount of times you want )
{
    RandomString += letters_numbers[rand() % letters_numbers.size()]; 
// Possibly add 1 to the % letters_numbers.size()
}

cout<< "Random string: " << RandomString;

EDIT - you could do it with ASCII values, but it's simpler this way, IMO

Using rand() to generate your random string isn't very secure (at all).

Originally Posted by Salem

Using rand() to generate your random string isn't very secure (at all).

Why do you need security when generating random things?
Let's say you get e8rt1aadhse4y88t. Even if it sometimes repeats the last letter, it is not guessable.

I am still not home... long day...

Lemme guess, you're trying to do this
http://en.wikipedia.org/wiki/Challen...authentication

Originally Posted by maxorator

Why do you need security when generating random things?
Let's say you get e8rt1aadhse4y88t. Even if it sometimes repeats the last letter, it is not guessable.

I am still not home... long day...

rand() is deterministic; each value it returns is mathematically based on the previous value. It is not really random at all. If you srand() with the time, as many do, then simply knowing the approximate time the string was created could narrow the search to only a few thousand possibilities.

Even worse, if you had an app that seeded once and then generated many passwords, if you determined the seed value, you'd know every single password that it would generate until the generator was re-seeded.

rand() is deterministic; each value it returns is mathematically based on the previous value. It is not really random at all.

This is true, but a cryptographic PRNG used correctly would suffice for security, even though it too would be deterministic.

If you srand() with the time, as many do, then simply knowing the approximate time the string was created could narrow the search to only a few thousand possibilities.

That is not the fault of rand(), but of the way the seeding was done.

Even worse, if you had an app that seeded once and then generated many passwords, if you determined the seed value, you'd know every single password that it would generate until the generator was re-seeded.

The point is that with the typical implementations of rand(), an attacker may be able to determine the seed value. With a cryptographic PRNG, an attacker's job would be considerably more difficult.