using System;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public static void Main()

    {

        string keyPrev;     

        for(long i=0; i < 2000000; i++) {

            keyPrev = GenerateUniqueString(8);

            if (keyPrev == GenerateUniqueString(8)) {

                Console.WriteLine("Doppione!!! - " + keyPrev);

                break;

            }

        }

        Console.WriteLine("Batch completato, 4.000.000 di chiavi generate.");

        Console.WriteLine(GenerateUniqueString(8));

    }   

    public static string GenerateUniqueString(byte stringSize)

    {               

        char[] chars = new char[62];

        string a;

        a = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890-_";

        chars = a.ToCharArray();

        int size  = stringSize;

        byte[] data = new byte[1];

        RNGCryptoServiceProvider  crypto = new RNGCryptoServiceProvider();

        crypto.GetNonZeroBytes(data);

        size =  stringSize; 

        data = new byte[size];

        crypto.GetNonZeroBytes(data);

        StringBuilder result = new StringBuilder(size);

        foreach(byte b in data)

        {

            result.Append(chars[b % (chars.Length - 1)]);

        }

        return result.ToString();

    }

​

}