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About the Author:

Dejan Lukan is a security researcher for InfoSec Institute and penetration tester from Slovenia. He is very interested in finding new bugs in real world software products with source code analysis, fuzzing and reverse engineering. He also has a great passion for developing his own simple scripts for security related problems and learning about new hacking techniques. He knows a great deal about programming languages, as he can write in couple of dozen of them. His passion is also Antivirus bypassing techniques, malware research and operating systems, mainly Linux, Windows and BSD. He also has his own blog available here: http://www.proteansec.com/.

MSDOS and the Interrupt Vector Table (IVT)


Upon booting up MSDOS, we can observe the memory using the “mem /d /p” command, which will show us exactly which part of memory is used by the system, […]


Memory Models


We know about user mode and kernel mode, and how programs in user-mode can only use the memory from 0×00000000 to 0x7FFFFFFF, while the system uses the memory from […]


Presenting Registers


Let’s present all of the registers, as seen in OllyDbg:

Let’s explain this picture a little better. At the top of the picture, the general purpose registers are given. The […]


Introduction to Kernel Debugging


Before trying to debug the kernel, we must first understand a few things. We must know what the Rings in computer security are. Let’s take a look at the […]


Reverse Engineering If Statements


Summary: In this article, we’ll present a simple program that uses ‘if’ statements and then we’ll try to reverse engineer the compiled version of the program to figure out […]


Reversing Switch Statements


In this article we’ll take a look at all the optimizations the compilers use to assembly the high-level switch statements into their assembly representations.

Switch Statements

The first example that we’ll […]


Introduction to SoftICE

It’s often the case that we need to debug a kernel application, like device driverS, system calls, interrupt routines, or some other kernel application. In this article we’ll talk […]


Cracking the Defender: The Deobfuscated Code


So far we’ve taken a look at the obfuscation routine and how it deobfuscates the instructions in the loc_4033D1. At the beginning point, the overview navigator will look like […]


Reversing Loops


Every program nowdays contains branch statements where the decision making happens and loops where we’re repeating some piece of code. Obviously, we could write a program that wouldn’t use […]


IDA Program Patching


It’s not a rare occurrence when we want to load a binary executable in a debugger, change some bytes and then save the changed binary to a hard drive, […]


Cracking the Defender: Deobfuscation Routine


In the previous tutorial we discussed a basic introduction to the Defender program. We’ve also looked at the sub_402EA8, which returns the base address of the ntdll.dll library in […]


Linear Sweep vs Recursive Disassembling Algorithm


We know that there are two ways of disassembling a binary executable into its assembler instructions. The first technique is linear sweep algorithm and the second is recursive disassembling. […]


Cracking the Defender: Basic Information and sub_402EA8 Function


Defender is an advanced crackme that was written by the Eldad Eilam for the purpose of reverse engineering. It contains several advanced protection mechanisms that a reverse engineer needs […]


Anti-Debugging: Detecting System Debugger


In the previous tutorial, we’ve talked about techniques that harden the reverse engineering of the executable and then we looked at anti-debugging techniques. We’ve mentioned the IsDebuggerPresent function and […]



Before we begin, we must mention that it’s impossible to completely prevent reversing. What is possible is that we can place as many obstacles on the way as we […]


IDA Pro Configuration Options

Configuration Files

We know that some of the Ida’s settings are saved in the .idb archive database files, but are not actually persisted across global Ida settings. Configuration files are […]


IDA Pro: IDC, SDK and Remote Debugging Overview

In this article, we won’t be going too deep into Ida scripting. Instead, we’ll present what an IDC is and how it can be used to enhance the capabilities […]


Facebook Hacker Cup 2013 Qualification Round: Find the Min

In the last two days, I described on this page my efforts at cracking the Facebook Hacker Cup 2013 challenge – three separate puzzles. Today we will examine the […]


Facebook Hacker Cup 2013 Qualification Round: Beautiful strings

Here’s my follow-on to the Facebook Hacker Cup. Yesterday, I told you about my take on the Balanced Smileys puzzle. Today, we’ll discuss the easiest challenge, Beautiful Strings. The […]


Facebook Hacker Cup 2013 Qualification Round: Balanced Smileys

I must admit that I was a little bit hesitant whether or not I should enter the Facebook Hacker Cup, but I did it anyway just for the fun […]