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Reverse Engineering Tutorial For begginer's

Reverse Engineering Tutorial For beginner's......

In simple words reverse engineering is the act to modify the code of  the application to make it work our way, Reverse engineering a very complicated topic and is very difficult to understand for newbie's as it requires a prior knowledge of assembly language, However in this article I will show you step by step how you can crack an application with reverse engineering.

Requirements

You will require the following things:

1.OllyDBG (http://download.cnet.com/OllyDbg/3000-2383_4-10213042.html)

2.Crack Me App (crackmes.de/users/tcn30/password_app/download)

Method

1.Once you have downloaded both OllyDBG and Crack Me App start the crack me app

2.Enter any password click ok

3.You will the following error

You are not authorized to use the application


4.Now open OllyDBG and open the Crack me app in it.


5.Now once you have opened the crack me app in OllyDBG, Right click there and goto search and then click on "All Reference Text Strings"

6.Now Right click there and click on "Search For text"

7.Search For the error which you got when you tried to log into the application ("You are not authorized to use the application")

8.Once you have found the error click on it and you will be bought to the following screen:

9.Now as you scroll upwards you will find the following line:

JE SHORT Password.00457728

This is a conditional jump which means that if the condition is right then it will jump to 00457728 Which leaves us to the message "You are not authorized to use the application" and if the condition is not satisfied it just continues reading the code, So we don't want this jump to work as we don't want to get the error message

Now there are two ways to remove this message:
1.We can either fill it with NOP's and make this conditional jump not work

2. we can change JE SHORT Password.00457728 to JNE SHORT Password.00457728, JNE(Jump If Not Equal) means that if the password is correct it will give you the bad message and if the password is incorrect it will give you the correct message

You can use any methods it's your choice, Now in this tutorial I will use the second method to use the method follow the steps given below:
1.Double click the line JE SHORT Password.00457728 and simple change it to JNE SHORT Password.00457728 and click assemble

2.Next Press the blue play button at the top which will start the application

3.Now just enter the password and it will give you the correct message.


I hope this tutorial will be helpful to clear the basics of reverse engineering and application cracking, However in the upcoming tutorials I will go in a bit advanced.
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