Confusing Disassemblers in .NET

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Confusing Disassemblers
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Linear Sweep Disassemblers Recursive Traversal Disassemblers Applications
Quick Response Code barcode library for .net
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337 338 343
recognizing qr-code in .net
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Code Obfuscation Control Flow Transformations
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Opaque Predicates Confusing Decompilers Table Interpretation
Barcode barcode library in .net
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344 346
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346 348 348
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Contents
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Inlining and Outlining Interleaving Code Ordering Transformations 353 354 355
Upc A barcode library on .net
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Data Transformations
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Modifying Variable Encoding Restructuring Arrays
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355 356
Access msi plessey for .net
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Conclusion 11 Breaking Protections Patching Keygenning Ripping Key-Generation Algorithms Advanced Cracking: Defender
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Reversing Defender s Initialization Routine Analyzing the Decrypted Code SoftICE s Disappearance Reversing the Secondary Thread Defeating the Killer Thread Loading KERNEL32.DLL Reencrypting the Function Back at the Entry Point Parsing the Program Parameters Processing the Username Validating User Information Unlocking the Code Brute-Forcing Your Way through Defender
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356 357 358 364 365 370
Linear Barcode barcode library with office word
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377 387 396 396 399 400 401 402 404 406 407 409 409
None code 39 extended readeron none
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Protection Technologies in Defender
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Localized Function-Level Encryption Relatively Strong Cipher Block Chaining Reencrypting Obfuscated Application/Operating System Interface Processor Time-Stamp Verification Thread Runtime Generation of Decryption Keys Interdependent Keys User-Input-Based Decryption Keys Heavy Inlining
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415 415 416 416 417 418 418 419 419
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Conclusion
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Part IV
Beyond Disassembly
423 424 426
426 428 428
12 Reversing .NET Ground Rules .NET Basics
Managed Code .NET Programming Languages Common Type System (CTS)
Intermediate Language (IL)
The Evaluation Stack Activation Records
430 430
Contents
IL Instructions IL Code Samples Counting Items A Linked List Sample 430 433 433 436
Decompilers Obfuscators
Renaming Symbols Control Flow Obfuscation Breaking Decompilation and Disassembly
443 444
444 444 444
Reversing Obfuscated Code
XenoCode Obfuscator DotFuscator by Preemptive Solutions Remotesoft Obfuscator and Linker Remotesoft Protector Precompiled Assemblies Encrypted Assemblies
446 448 451 452 453 453
Conclusion 13 Decompilation Native Code Decompilation: An Unsolvable Problem Typical Decompiler Architecture Intermediate Representations
Expressions and Expression Trees Control Flow Graphs
455 457 457 459 459
461 462
The Front End
Semantic Analysis Generating Control Flow Graphs
463 464
Code Analysis
Data-Flow Analysis Single Static Assignment (SSA) Data Propagation Register Variable Identification Data Type Propagation Type Analysis Primitive Data Types Complex Data Types Control Flow Analysis Finding Library Functions
466 467 468 470 471 472 472 473 475 475
The Back End Real-World IA-32 Decompilation Conclusion Appendix A Deciphering Code Structures Appendix B Understanding Compiled Arithmetic Appendix C Deciphering Program Data Index
476 477 477 479 519 537 561
Introduction
Welcome to Reversing: Secrets of Reverse Engineering. This book was written after years of working on software development projects that repeatedly required reverse engineering of third party code, for a variety of reasons. At first this was a fairly tedious process that was only performed when there was simply no alternative means of getting information. Then all of a sudden, a certain mental barrier was broken and I found myself rapidly sifting through undocumented machine code, quickly deciphering its meaning and getting the answers I wanted regarding the code s function and purpose. At that point it dawned on me that this was a remarkably powerful skill, because it meant that I could fairly easily get answers to any questions I had regarding software I was working with, even when I had no access to the relevant documentation or to the source code of the program in question. This book is about providing knowledge and techniques to allow anyone with a decent understanding of software to do just that. The idea is simple: we should develop a solid understanding of low-level software, and learn techniques that will allow us to easily dig into any program s binaries and retrieve information. Not sure why a system behaves the way it does and no one else has the answers No problem dig into it on your own and find out. Sounds scary and unrealistic It s not, and this is the very purpose of this book, to teach and demonstrate reverse engineering techniques that can be applied daily, for solving a wide variety of problems. But I m getting ahead of myself. For those of you that haven t been exposed to the concept of software reverse engineering, a little introduction is in order.
xxiii
xxiv Introduction
Reverse Engineering and Low-Level Software
Before we get into the various topics discussed throughout this book, we should formally introduce its primary subject: reverse engineering. Reverse engineering is a process where an engineered artifact (such as a car, a jet engine, or a software program) is deconstructed in a way that reveals its innermost details, such as its design and architecture. This is similar to scientific research that studies natural phenomena, with the difference that no one commonly refers to scientific research as reverse engineering, simply because no one knows for sure whether or not nature was ever engineered. In the software world reverse engineering boils down to taking an existing program for which source-code or proper documentation is not available and attempting to recover details regarding its design and implementation. In some cases source code is available but the original developers who created it are unavailable. This book deals specifically with what is commonly referred to as binary reverse engineering. Binary reverse engineering techniques aim at extracting valuable information from programs for which source code in unavailable. In some cases it is possible to recover the actual source-code (or a similar high-level representation) from the program binaries, which greatly simplifies the task because reading code presented in a high-level language is far easier than reading low-level assembly language code. In other cases we end up with a fairly cryptic assembly language listing that describes the program. This book explains this process and why things work this way, while describing in detail how to decipher the program s code in a variety of different environments.
I ve decided to name this book Reversing , which is the term used by many online communities to describe reverse engineering. Because the term reversing can be seen as a nickname for reverse engineering I will be using the two terms interchangeably throughout this book.
Most people get a bit anxious when they try to imagine trying to extract meaningful information from an executable binary, and I ve made it the primary goal of this book to prove that this fear is not justified. Binary reverse engineering works, it can solve problems that are often incredibly difficult to solve in any other way, and it is not as difficult as you might think once you approach it in the right way. This book focuses on reverse engineering, but it actually teaches a great deal more than that. Reverse engineering is frequently used in a variety of environments in the software industry, and one of the primary goals of this book is to explore many of these fields while teaching reverse engineering.