What is the method of this encoding?

[ImacrosGuy]

Hey,

I'm trying to figure out how to decode a javascript based captcha.

Some examples:

'lAFqxqYHhlkEaZyNPO0NGQGwKjOliIxFMFZMOVgNW%2fg%3d' == '6HCOI'

'WHwvopiJKG0oKCrhkearTIkWkYl%2fGLcebPNwWODRfBw%3d' == '7JDBK'

Engine of the captcha:

[COLOR=#000000]<%@ WebHandler Language="C#" Class="GetImgText" %>[/COLOR]/*

Scrambled text generator.
Developed by: Aref Karimi
Email: [email protected]
Last update: 20 October 2009

This code is free to use. 
 
*/
using System;
using System.Web;
using System.Collections.Generic;
using System.Drawing;

public class GetImgText : IHttpHandler {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "image/jpeg";
        var CaptchaText = SecurityHelper.DecryptString(
            Convert.FromBase64String(context.Request.QueryString["CaptchaText"]));
        if (CaptchaText != null)
        {
            List<Letter> letter = new List<Letter>();
            int TotalWidth = 0;
            int MaxHeight = 0;
            foreach (char c in CaptchaText)
            {
                var ltr = new Letter(c);
                letter.Add(ltr);
                int space = (new Random()).Next(5) + 1;
                ltr.space = space;
                System.Threading.Thread.Sleep(1);
                TotalWidth += ltr.LetterSize.Width+space;
                if (MaxHeight < ltr.LetterSize.Height)
                    MaxHeight = ltr.LetterSize.Height;
                System.Threading.Thread.Sleep(1);
            }
            const int HMargin = 5;
            const int VMargin = 3;

            Bitmap bmp = new Bitmap(TotalWidth + HMargin, MaxHeight + VMargin);
            var Grph = Graphics.FromImage(bmp);
            Grph.FillRectangle(new SolidBrush(Color.Lavender), 0, 0, bmp.Width, bmp.Height);
            Pixelate(ref bmp);
            Grph.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            Grph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            int xPos = HMargin;
            foreach (var ltr in letter)
            {
                Grph.DrawString(ltr.letter.ToString(), ltr.font, new SolidBrush(Color.Navy), xPos, VMargin );
                xPos += ltr.LetterSize.Width + ltr.space;
            }
            
            bmp.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }
    private void Pixelate(ref Bitmap bmp)
    {
        Color[] Colors = { Color.Gray , Color.Red, Color.Blue, Color.Olive };
        for (int i = 0; i < 200; i++)
        {
            var rnd = new Random(DateTime.Now.Millisecond);
            var grp = Graphics.FromImage(bmp);
            Image background = Image.FromFile(HttpContext.Current.Server.MapPath("~/images/captcha/captcha3.jpg"));
            grp.DrawImage(background, new Rectangle(0, 0, bmp.Width, bmp.Height));
        }
    }
 [COLOR=#000000]}[/COLOR]

 

[divok]

http://www.insidepro.com/hashes.php?lang=eng

 

[Macthetrix]

The whole point of a hash is that you cant reverse it.
A database stores hashed passwords so even if someone gets access to it he wont be able to reverse it and get the passwords.

 

[ImacrosGuy]

http://www.insidepro.com/hashes.php?lang=eng

The whole point of a hash is that you cant reverse it.
A database stores hashed passwords so even if someone gets access to it he wont be able to reverse it and get the passwords.

So there is no chance to break the captcha from the codes i guess?

 

[Nitin Kumar]

HTTP protocol uses ASCII for character set for URLs and any character outside the ASCII character set needs to be encoded using a special format so that it does not break the protocol.