using System;

using System.IO;

using System.Text;

using System.Security.Cryptography;

public class Program

{

    public static void Main()

    {

        //The random stuff is to add to add a bit more randomness than just time-dependent Random().

        var r3 = new System.Security.Cryptography.RNGCryptoServiceProvider();

        int length=16;

        var bytes = new byte[length];

        r3.GetBytes(bytes);

        var bc = "abcdefghijklmnopqrstuvwzABCDEFGHIJKLMNOPQRSTUVWZ";

        var o9 = "0123456789!?-:@+=%_*!?-:@+=%_*";

        var res = "";

        for (int i = 0; i < length; i++)

        {

            var s = "";

            if (i / (double)length < 0.7)

                s = bc;

            else

                s = o9;

​

            var ir = bytes[i] % s.Length;

            res += s[ir];

        }

        Console.WriteLine(res);

    }

}