binary-analysis

Binary Analysis

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

Quick Reference

Tool	Purpose	Install
strings	Extract printable text from binaries	Built-in (binutils)
binwalk	Firmware analysis, file extraction	pip install binwalk or cargo install binwalk
hexdump	Hex/ASCII dump	Built-in
xxd	Hex dump with reverse capability	Built-in (vim)
file	Identify file type	Built-in

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)

Signature	Hex	File Type
PK	50 4B 03 04	ZIP archive
Rar!	52 61 72 21	RAR archive
7z	37 7A BC AF	7-Zip
ELF	7F 45 4C 46	Linux executable
MZ	4D 5A	Windows executable
PNG	89 50 4E 47	PNG image
JFIF	FF D8 FF E0	JPEG image
sqsh	73 71 73 68	SquashFS
hsqs	68 73 71 73	SquashFS (LE)

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