10 Reverse Engineering Interview Questions and Answers

Reverse engineering is a critical skill in various fields such as cybersecurity, software development, and hardware design. It involves deconstructing software or hardware to understand its components and functionality, often to identify vulnerabilities, improve compatibility, or enhance security measures. Mastery of reverse engineering requires a deep understanding of system architecture, programming languages, and analytical techniques.

This article provides a curated selection of reverse engineering questions and answers to help you prepare for your upcoming interview. By familiarizing yourself with these questions, you will gain insights into the key concepts and methodologies that are essential for demonstrating your expertise in reverse engineering.

Reverse Engineering Interview Questions and Answers

1. Explain the difference between static and dynamic analysis.

Static analysis involves examining a program’s code or binary without executing it, using tools like disassemblers and decompilers to understand its structure and behavior. It allows for a detailed examination without the risk of executing harmful instructions. Dynamic analysis, in contrast, involves running the program in a controlled environment to observe its real-time behavior, using tools like debuggers and sandbox environments. This approach is useful for identifying runtime issues and understanding complex interactions.

2. Write a Python script to read the headers of a PE (Portable Executable) file.

A PE (Portable Executable) file is a format for executables and DLLs in Windows. Reading its headers can reveal the structure and behavior of the executable. The pefile library in Python simplifies parsing and analyzing PE files.

import pefile

def read_pe_headers(file_path):
    pe = pefile.PE(file_path)
    
    print("DOS Header:")
    print(pe.DOS_HEADER)
    
    print("\nNT Headers:")
    print(pe.NT_HEADERS)
    
    print("\nFile Header:")
    print(pe.FILE_HEADER)
    
    print("\nOptional Header:")
    print(pe.OPTIONAL_HEADER)

# Example usage
read_pe_headers('example.exe')

3. What is the purpose of a disassembler?

A disassembler converts machine code back into assembly language, aiding in understanding a program’s inner workings when the source code is unavailable. This is useful for debugging, malware analysis, and understanding software operations. Popular disassemblers include IDA Pro, Ghidra, and Radare2.

4. Write a Python function to decrypt a string encrypted with a simple XOR cipher.

XOR encryption is a simple symmetric technique where the same key is used for both encryption and decryption. The XOR operation is applied between the plaintext and the key to produce the ciphertext. To decrypt, the same operation is applied between the ciphertext and the key.

def xor_decrypt(ciphertext, key):
    decrypted = ''.join(chr(ord(c) ^ ord(k)) for c, k in zip(ciphertext, key))
    return decrypted

ciphertext = "encrypted_string"
key = "key"
decrypted_string = xor_decrypt(ciphertext, key)
print(decrypted_string)

5. What are some common code obfuscation techniques, and how can they be countered?

Code obfuscation makes code difficult to understand to protect intellectual property. Techniques include identifier renaming, control flow obfuscation, string encryption, dead code insertion, and code flattening. These can be countered with deobfuscation tools, static and dynamic analysis, and manual reverse engineering.

6. Describe the steps you would take to analyze a suspected malware sample.

Analyzing a suspected malware sample involves several steps: initial triage and static analysis to gather basic information, dynamic analysis to observe behavior in a controlled environment, behavioral analysis to understand system impact, code analysis to examine the code, memory analysis to identify in-memory artifacts, and reporting findings with mitigation strategies.

7. What is a control flow graph, and how is it useful?

A control flow graph (CFG) represents all paths a program might traverse during execution. Each node is a basic block, and edges represent control flow paths. CFGs aid in program analysis, optimization, malware analysis, and debugging by providing a clear view of execution flow.

8. Describe how you would perform binary patching to alter the behavior of a program.

Binary patching modifies a program’s binary code to alter its behavior. Steps include disassembly to understand structure, analysis to identify target instructions, modification using a hex editor or patching tool, and reassembly to test changes.

9. Explain symbolic execution and its applications in reverse engineering.

Symbolic execution analyzes programs by treating inputs as symbolic values, exploring multiple execution paths to identify vulnerabilities and understand behavior. Applications include vulnerability detection, program understanding, test case generation, and malware analysis.

10. What are some common anti-debugging techniques, and how can they be identified and bypassed?

Anti-debugging techniques hinder debugging and reverse engineering. Common methods include API-based detection, timing checks, exception-based detection, self-modifying code, and debugger flag checks. These can be identified and bypassed through static and dynamic analysis, patching, and emulation.