Binary Analysis

Binary Analysis

Tools for exploring and reverse engineering binary files, firmware, and unknown data.

When to Use This Skill

Quick Reference

strings - Extract Text from Binaries

Find human-readable strings embedded in binary files.

# Basic usage - find all printable strings (min 4 chars)
strings binary_file

# Set minimum string length
strings -n 10 binary_file          # Only strings >= 10 chars

# Show file offset of each string
strings -t x binary_file           # Hex offset
strings -t d binary_file           # Decimal offset

# Search for specific patterns
strings binary_file | grep -i password
strings binary_file | grep -E 'https?://'
strings binary_file | grep -i api_key

# Wide character strings (UTF-16)
strings -e l binary_file           # Little-endian 16-bit
strings -e b binary_file           # Big-endian 16-bit
strings -e L binary_file           # Little-endian 32-bit

# Scan entire file (not just initialized data sections)
strings -a binary_file

Common discoveries with strings:

• Hardcoded credentials, API keys
• URLs and endpoints
• Error messages (hints at functionality)
• Library versions
• Debug symbols and function names
• Configuration paths

binwalk - Firmware Analysis

Identify and extract embedded files, analyze entropy, find hidden data.

# Signature scan - identify embedded files/data
binwalk firmware.bin

# Extract all identified files
binwalk -e firmware.bin            # Extract to _firmware.bin.extracted/
binwalk --extract firmware.bin     # Same as -e

# Recursive extraction (extract files within extracted files)
binwalk -Me firmware.bin

# Entropy analysis - find compressed/encrypted regions
binwalk -E firmware.bin            # Generate entropy graph
binwalk --entropy firmware.bin

# Opcode analysis - identify CPU architecture
binwalk -A firmware.bin
binwalk --opcodes firmware.bin

# Raw byte extraction at offset
binwalk --dd='type:extension' firmware.bin

# Specific signature types
binwalk --signature firmware.bin   # File signatures only
binwalk --raw='\\x1f\\x8b' firmware.bin  # Search for gzip magic bytes

binwalk output interpretation:

DECIMAL       HEXADECIMAL     DESCRIPTION
--------------------------------------------------------------------------------
0             0x0             TRX firmware header
28            0x1C            LZMA compressed data
1835008       0x1C0000        Squashfs filesystem, little endian

hexdump / xxd - Raw Hex Analysis

# Hex + ASCII dump
hexdump -C binary_file
xxd binary_file

# Dump specific byte range
xxd -s 0x100 -l 256 binary_file    # 256 bytes starting at offset 0x100

# Just hex, no ASCII
hexdump -v -e '/1 "%02x "' binary_file

# Create hex dump that can be reversed
xxd binary_file > hex.txt
xxd -r hex.txt > reconstructed_binary

# Find specific bytes
xxd binary_file | grep "504b"      # Look for PK (ZIP signature)

file - Identify File Types

# Basic identification
file unknown_file
file -i unknown_file               # MIME type

# Check multiple files
file *

# Follow symlinks
file -L symlink

Common Analysis Workflows

Unknown Binary Exploration

# 1. Identify file type
file mystery_file

# 2. Check for embedded files
binwalk mystery_file

# 3. Extract strings
strings -n 8 mystery_file | head -100

# 4. Look at hex header
xxd mystery_file | head -20

# 5. Check entropy (compressed/encrypted?)
binwalk -E mystery_file

Firmware Analysis

# 1. Initial scan
binwalk firmware.bin

# 2. Extract everything
binwalk -Me firmware.bin

# 3. Explore extracted filesystem
find _firmware.bin.extracted -type f -name "*.conf"
find _firmware.bin.extracted -type f -name "passwd"

# 4. Search for secrets
grep -r "password" _firmware.bin.extracted/
strings -n 10 firmware.bin | grep -i -E "(pass|key|secret|token)"

Finding Hidden Data

# Check for data after end of file
binwalk -E file.jpg               # Entropy spike at end = appended data

# Look for embedded archives
binwalk file.jpg | grep -E "(Zip|RAR|7z|gzip)"

# Extract with offset
dd if=file.jpg of=hidden.zip bs=1 skip=12345

File Signatures (Magic Bytes)

Tips

• Start with entropy: High entropy = compressed or encrypted
• Look for strings first: Often reveals purpose quickly
• Check file headers: First 16 bytes often identify format
• Use recursive extraction: Firmware often has nested archives
• Save offsets: Note interesting locations for targeted extraction