Generating every character combination up to a certain word length

Question

I am doing a security presentation for my Computer and Information Security course in a few weeks time, and in this presentation I will be demonstrating the pros and cons of different attacks (dictionary, rainbow and bruteforce). I am do the dictionary and rainbow attacks fine but I need to generate the bruteforce attack on the fly. I need to find an algorithm that will let me cycle though every combination of letter, symbol and number up to a certain character length.

So as an example, for a character length of 12, the first and last few generations will be:

a
ab
abc
abcd
...
...
zzzzzzzzzzzx
zzzzzzzzzzzy
zzzzzzzzzzzz

But it will also use numbers and symbols, so it's quite hard for me to explain... but I think you get the idea. Using only symbols from the ASCII table is fine.

I can kind of picture using an ASCII function to do this with a counter, but I just can't work it out in my head. If anyone could provide some source code (I'll probably be using C#) or even some pseudo code that I can program a function from that'd be great.

Thank you in advance. :)

Answer 1

A recursive function will let you run through all combinations of ValidChars:

    int maxlength = 12;
    string ValidChars;
    private void Dive(string prefix, int level)
    {
        level += 1;
        foreach (char c in ValidChars)
        {
            Console.WriteLine(prefix + c);
            if (level < maxlength)
            {
                Dive(prefix + c, level);
            }
        }
    }

Assign the set of valid characters to ValidChars, the maximum length of string you want to maxlength, then call Dive("", 0); and away you go.