Software Reverse Engineering is the process of analyzing a software system to understand its design, requirements, and functionality by examining its code. It helps rebuild knowledge about how a program works by extracting information from existing software.
- Breaks down existing code to understand system design and logic
- Helps recover missing documentation or specifications
- Builds a structured program database from analyzed code
- Useful for debugging, maintenance, and security analysis
Objectives and Goals of Reverse Engineering
Reverse engineering is used to analyze existing systems to understand their structure, behavior, and design in order to improve, reuse, or rebuild them efficiently.
1. Understanding System Complexity
- Helps analyze complex systems to understand architecture, design patterns, and relationships between components
- Reveals how different parts of a system interact
- Simplifies analysis of large or poorly documented systems
- Supports better system comprehension and decision-making
2. Recovering Lost Information and System Knowledge
- Reconstructs system logic when source code or documentation is unavailable
- Helps rebuild data structures and functional behavior
- Provides higher-level representation of existing systems
- Supports redevelopment, migration, or system continuation
3. Security Analysis and Vulnerability Detection
- Used to analyze malware and understand malicious behavior
- Identifies vulnerabilities, weaknesses, and exploit techniques
- Helps uncover hidden threats and system risks
- Supports development of stronger security defenses
4. Maintenance, Debugging and System Improvement
- Helps debug and fix issues in legacy or poorly documented systems
- Enables patching without original source code access
- Improves system stability and long-term usability
- Ensures continued functioning of older systems
5. Integration, Customization and Reuse
- Helps understand internal system structure for modification or extension
- Supports integration with other systems or platforms
- Enables reuse of existing components in new applications
- Reduces development effort and improves efficiency
6. System Optimization and Abstraction
- Identifies reusable patterns and improves resource utilization
- Helps reduce development cost and avoid rebuilding from scratch
- Converts low-level details into higher-level models for easier analysis
- Supports system optimization and redesign
Reverse Engineering for Data Understanding
Reverse engineering of data is performed at different levels of abstraction and is often one of the first steps in reengineering.
- Program Level: At the program level, internal data structures are analyzed and reverse engineered as part of understanding how the software works.
- System Level: At the system level, global data structures such as files and databases are redesigned to support modern database systems (e.g., moving from flat-file systems to relational or object-oriented databases).
Internal Data Structures
Focuses on identifying and defining classes of objects by analyzing program data.
- Approach: Program code is examined to group related variables together. Data organization in the code often reveals abstract data types.
- Common Indicators: Structures such as records, files, lists, and arrays often help identify potential classes of objects.
Database Structures
A database contains data objects and their relationships. Reverse engineering focuses on understanding existing schemas before redesigning or migrating them.
Key Steps:
- Build an initial object model: Create a preliminary model based on existing database structures.
- Identify candidate keys: Analyze attributes to determine which ones act as references or pointers to other records or tables, and mark them as candidate keys.
- Refine tentative classes: Improve and restructure the initial object grouping based on analysis.
- Define generalizations: Establish higher-level relationships and hierarchies among data objects.
Reverse Engineering to Understand Processing
Reverse engineering is used to understand how a program works by extracting procedural abstractions from its source code.
1. Levels of Abstraction
The code is analyzed at different levels:
- System level
- Program level
- Component level
- Pattern level
- Statement level
2. System Representation
Each program in the system represents a high-level functional unit. A block diagram is prepared to show the interaction between these functional units.
3. Component Analysis
Each component performs a specific subfunction and represents a procedural abstraction. A processing narrative is written for each component to describe its behavior.
4. Tool Support
For large systems, reverse engineering is done using semi-automated tools that help analyze and interpret the code.
5. Output Usage
The extracted information is used in restructuring and forward engineering to complete the reengineering process.
Steps of Software Reverse Engineering
- Collection Information: This step focuses on collecting all possible information (i.e., source design documents, etc.) about the software.
- Examining the Information: The information collected in step-1 is studied so as to get familiar with the system.
- Extracting the Structure: This step concerns identifying program structure in the form of a structure chart where each node corresponds to some routine.
- Recording the Functionality: During this step processing details of each module of the structure, charts are recorded using structured language like decision table, etc.
- Recording Data Flow: From the information extracted in step-3 and step-4, a set of data flow diagrams is derived to show the flow of data among the processes.
- Recording Control Flow: The high-level control structure of the software is recorded.
- Review Extracted Design: The design document extracted is reviewed several times to ensure consistency and correctness. It also ensures that the design represents the program.
- Generate Documentation: Finally, in this step, the complete documentation including SRS, design document, history, overview, etc. is recorded for future use.
Reverse Engineering Tools
Reverse engineering tools analyze source code and generate design representations such as structural, procedural, data, and behavioral models. Since manual reverse engineering is time-consuming, automated tools are used.
Common tools include:
- CIAO and CIA: A graphical navigator for software and web repositories, along with a collection of reverse engineering tools.
- Rigi: A visual software understanding tool used to analyze and explore software systems.
- Bunch: A tool used for software clustering and modularization.
- GEN++: An application generator that supports the development of analysis tools for the C++ programming language.
- PBS (Programmer’s Bookshelf System): A set of tools used for extracting and visualizing the architecture of software programs.