Trainer Name: Tim Blazytko

Title: Software Deobfuscation Techniques

Duration: 3 Days

Dates: March 6, 2023 To March 8, 2023

Training Objectives

Code obfuscation has become a vital tool to protect, for example, intellectual property against competitors. In general, it attempts to impede program understanding by making the to-be-protected program more complex. As a consequence, a human analyst reasoning about the obfuscated code has to overcome this barrier by transforming it into a representation that is easier to understand.

In this training, we get to know state-of-the-art code obfuscation techniques and look at how these complicate reverse engineering. Afterwards, we gradually familiarize ourselves with different deobfuscation techniques and use them to break obfuscation schemes in hands-on sessions. Thereby, participants will deepen their knowledge of program analysis and learn when and how (not) to use different techniques.

First, we have a look at important code obfuscation techniques and discuss how to attack them. Afterwards, we analyze a virtual machine-based (VM-based) obfuscation scheme, learn about VM hardening techniques and how to tackle them.

In the second part, we cover SMT-based program analysis. In detail, students learn how to solve program analysis problems with SMT solvers, how to prove characteristics of code and how to deobfuscate mixed Boolean-Arithmetic.

Before we use symbolic execution to automate large parts of code deobfuscation, we first introduce intermediate languages and compiler optimizations to simplify industrial-grade obfuscation schemes. Following, we use symbolic execution to automate SMT-based program analysis and break opaque predicates. Finally, we learn how to write disassemblers for virtualization-based obfuscators and how to reconstruct the original code.

The last part covers program synthesis, an approach to simplify code based on its semantic behavior. After collecting input-output pairs from binary code, we not only learn how to simplify large expression trees, but also how we can verify the correctness of simplifications. Then, we use program synthesis to deobfuscate mixed Boolean-Arithmetic and learn the semantics of VM instruction handlers.


Note that the training focuses on hands-on sessions. While some lecture parts provide an understanding of when to use which method, various hands-on sessions teach how to use them to build custom purpose tools for one-off problems. The trainer actively supports the students to successfully solve the given tasks. After a task is completed, we discuss different solutions in class. Furthermore, students receive detailed reference solutions that can be used during and after the course.

While the hands-on sessions use x86 assembly, all tools and techniques can also be applied to other architectures such as MIPS, PPC or ARM.

Training level: Advanced

Training Outline

The training orientates at the following outline:
  • Introduction to Code (De)obfuscation
    • Motivation
    • Application scenarios
    • Program analysis techniques
  • Code Obfuscation Techniques
    • Opaque predicates
    • Control-flow flattening
    • Mixed Boolean-Arithmetic
    • Virtual machines
    • Virtual machine hardening
  • Code Deobfuscation Techniques
    • Compiler optimizations
    • Reconstructing control flow
    • SMT-based program analysis
    • Taint analysis
    • Symbolic execution
    • Program synthesis
  • Compiler Optimizations
    • Dead code elimination
    • Constant propagation/folding
    • Static single assignment (SSA)
    • Optimizing obfuscated code
  • SMT-based Program Analysis
    • SAT and SMT solvers
    • Encoding programs analysis problems for SMT solvers
    • Proving semantic equivalence
    • Proving properties of a piece of code
    • Solving complex program constraints
    • Deobfuscating mixed Boolean-Arithmetic
  • Symbolic Execution
    • Intermediate languages for reverse engineering
    • Symbolic and semantic simplification of obfuscated code
    • Automation in reverse engineering
    • Identifying virtual machine components
    • Interaction with SMT solvers
    • Breaking opaque predicates
    • Writing disassemblers for virtualization-based obfuscators
  • Program Synthesis
    • Concept of program synthesis
    • Learning code semantics based on its input/output behavior
    • Obtaining input/output pairs from code
    • Methods to simplify large expression trees
    • Proving the correctness of simplifications
    • Deobfuscating mixed Boolean-Arithmetic
    • Learning semantics of VM instruction handlers

Who Should Attend?

This class is intended for students who have basic experience in reverse engineering and have to deal with obfuscated code. Furthermore, the course is also interesting for experienced reverse engineers who aim to deepen their understanding in program analysis techniques and code (de)obfuscation.

What to Bring?

Students should have access to a computer with 4 GB RAM (minimum) and at least 20 GB disk space. Furthermore, they should install a disassembler of their choice (e.g., IDA or Ghidra) as well as virtualization software such as Virtual Box or VMware. Students will be provided with a Linux VM containing all necessary tools and setups.

Training Prerequisite

  • Basic reverse engineering skills
  • Familiarity with x86 assembly and Python

What attendees will be provided?

  • presentation slides
  • tasks + solutions for in-class and after-class practice
  • a Linux VM containing all necessary tools and setups

What to Expect?

Learning Objectives

  • Get to know the state-of-the-art of code obfuscation and deobfuscation techniques
  • Learn compiler optimizations, SMT-based program analysis, symbolic execution and program synthesis
  • Apply all techniques to break obfuscation schemes in various hands-on sessions
  • Write disassemblers for VM-based obfuscators and simplify complex arithmetic expressions

What not to expect?

  • An introduction into reverse engineering
  • An end-to-end deobfuscator which magically breaks all code obfuscation schemes

About the Trainer

Tim Blazytko is a well-known binary security researcher and co-founder of emproof. After working on novel methods for code deobfuscation, fuzzing and root cause analysis during his PhD, Tim now builds code obfuscation schemes tailored to embedded devices. Moreover, he gives trainings on reverse engineering & code deobfuscation, analyzes malware and performs security audits.