Reverse

Reverse Engineering

Shaochun Xu
Computer Science University of Windsor

Contents

   



What is Reverse Engineering (RE)? Why do we need Reverse Engineering? Scope and Tasks of Reverse Engineering Different Approaches RE tools Conclusions

What is Reverse Engineering ?
 You

have an unexpected case:

• • • •

You finished one course project using Java Your program runs OK But, by accident, you delete the java file How to hand in your project?

What is Reverse Engineering ?
 You

have an unexpected case:

• • • •

You finished one course project using Java Your program runs OK But, by accident, you delete the java file How to hand in your project?

 Reverse

Engineering

What is Reverse Engineering ?
Waterfall Model of software development
Requirement analysis design

Implementation
Testing and Maintenance

What is Reverse Engineering ?
Forward Engineering Requirements Design

Source Code
Behavior

What is Reverse Engineering ?
Forward Engineering Reverse Engineering

Requirements Design

Source Code
Behavior

What is Reverse Engineering ?
Abstraction System
Reverse Engineering Abstraction Forward Engineering Re-Implementation

Old system

New System

What is Reverse Engineering?
 RE

encompasses any activity that is done to determine how a product works, to learn the ideas and technology that were used in developing that product.  RE can be done at many levels
 RE

generally belongs to Software Maintenance

The Early Days of RE
 Law

of Software Revolution (Lehman, 1980)

 Fundamental

strategies for program comprehension (Brooks, 1983)  Taxonomy of Reverse Engineering (Chikofsky&Cross, 1990)  WCRE (Working Conference on R.E., 1990)  IWPC (Int. Workshop on Program Comprehension)

Why do we need RE ?

 Recovery  Assisting

of lost information with maintenance

• providing proper system documentation • identification of side effects and anomalies
 Migration

to another hw/sw platform
software reuse

 Facilitating

Why do we need RE ?
 Benefits

• • • •

maintenance cost savings quality improvements competitive advantages software reuse facilitation

Difficulties of Reverse Engineering
 Gap

between problem /solution domain  Gap between concrete and abstract  Gap between coherency/disintegration  Gap between hierarchical/associational

Scope and Task of Reverse Engineering
 program

understanding
Problem/Application domain

Mapping

Program/Implemen. domain

Scope and Task of Reverse Engineering
 Redocumentation

and/or document

generation  Recovery of design approach and design details at any level of abstraction  Identifying reusable components and components that need restructuring  Recovering business rules  Understanding high-level system description.

Discovery of Abstraction
 Discovery

of abstraction in large system

• maintenance purpose • evolution purpose • reengineering purpose

Levels of abstractions
 

Application
• Application concepts, business rule, policies

Function
• Logical and functional specification, non-functional requirement



Structure
• Data and control flow, dependency graphs • Structure and subsystem charts • Architectures



Implementation
• Symbol tables, source text

Different Approaches
 Restructuring

• Transformation from one representation to another at the same level,
Requirements Design Source code Behavior

Different Approaches
 Reverse

Engineering

• Design Recovery
– reproduce all the info for understanding the system

• Re-documentation
– provide different views of the system  Re-Engineering

• first phase --understanding the system • second phase--forward engineering

Different Approaches
Abstraction System
Reverse Engineering Abstraction Forward Engineering Re-Implementation

Old system

New System

Reverse Engineering Tools
 Analysis

Tools  Browsers  Object Server  Task Oriented Tools

Example--Java Decompiler
 How

to recover bytecode from .class file under Unix/Win with JDK?
% javap -c <filename> % javap -help (to see the options)

 Java

Decompilers

• ”ClassCracker” http://www.pcug.org.au/~mayon/ • “DeCafe Pro" from DeCafe, France at
http://decafe.hypermart.net/index.htm

• “SourceAgain" from Ahpah corp at http://www.ahpah.com

Example--Java Decompiler
 ClassCracker

2 Interface

Example--Java Decompiler
 Components

of ClassCracker 2

• Java decompiler
– retrieves Java source code from Java class files

• Java disassembler
– produces Java Assembly Code

• A Java class file viewer
– displays Java class file structures.

Example--Java Decompiler
 Features

of ClassCracker 2

• User visual interface. • Can decompile class files within zip or jar files. • Conversion mode (JAVA, JASM or JDUMP) is selectable • A Batc Mode allows multiple class files to be decompiled simultaneously • more…...

Example--Java Decompiler
 ClassCracker

2 System Requirements

• All platform (Window/Linus/Unix) • JDK /JRE
 Do

not believe it?
(==>myClass.class)

• From myClass_origin.class ==>myClass.java

• % javac myClass.java

• % diff myClass.class myClass_origin.class

Example--Java Decompiler
 ClassCracker

2.0--want to try it?

• Free download at http://www.pcug.org.au/~mayon/classcracker/ ccgetdemo.html • Only first three methods are decoded.
 Bridge

1.0---Free

• http://www.geocities.com/SiliconValley/Brid ge/8617/jad.html

Conclusions
 Reverse  RE

Engineering is a new research area among software maintenance includes activities of understanding the system and recovery info from system

 Program

understanding is the most important subset of Reverse Engineering
of abstraction is key issue

 Discovery

Questions ?