class-dump

class-dump is a tool for extracting Objective-C class definitions and method signatures from compiled Mach-O binaries (macOS, iOS). It generates header files that reveal class hierarchies, methods, and properties.

Installation

macOS

# Homebrew
brew install class-dump

# Build from source
git clone https://github.com/nygard/class-dump.git
cd class-dump
make
cp build/Release/class-dump /usr/local/bin/

# Download pre-built binary
# From: http://steqart.io/cdn/class-dump/3.5/class-dump
wget http://steqart.io/cdn/class-dump/3.5/class-dump
chmod +x class-dump
sudo mv class-dump /usr/local/bin/

Verify Installation

class-dump --version
class-dump --help

Basic Usage

Extracting Class Headers

# Extract headers from executable
class-dump /path/to/app.app/app > headers.h

# Extract to directory
class-dump -H /path/to/app.app/app -o headers/

# Extract framework
class-dump /System/Library/Frameworks/UIKit.framework/UIKit -o UIKit_headers/

# Extract library
class-dump -H /usr/lib/libSystem.dylib -o libSystem_headers/

Common Options

Option	Description
-H	Generate headers in directory
-o <dir>	Output directory
-r	Include run-time info
-s <sig>	Sort alphabetically by class name
-S	Sort classes by size
--arch	Specify architecture (i386, x86_64, arm, arm64)
--show-ivar-offset	Show instance variable offsets
--show-superclass	Show superclass

Working with App Bundles

iOS App Structure

# List app files
ls -la /path/to/MyApp.app/

# Key files:
# MyApp              - Main executable
# Frameworks/        - Embedded frameworks
# Info.plist         - App metadata
# PkgInfo            - Package type

Extracting from App

# Extract main app binary
class-dump -H /path/to/MyApp.app/MyApp -o MyApp_headers/

# Extract all frameworks
for fw in /path/to/MyApp.app/Frameworks/*.framework; do
    name=$(basename "$fw" .framework)
    class-dump -H "$fw/$name" -o "${name}_headers/"
done

# Extract specific framework
class-dump -H /path/to/MyApp.app/Frameworks/MyFramework.framework/MyFramework \
    -o MyFramework_headers/

Output Understanding

Header Format

// Example output

@interface UIViewController : UIResponder <NSCoding>
{
    UIView *_view;
    id <UIViewControllerTransitioningDelegate> _transitioningDelegate;
    UIStoryboardSegueTemplate *_segueTemplates;
    NSArray *_childViewControllers;
    // ... more ivars
}

@property(nonatomic, assign) BOOL modalPresentationCapturesStatusBarAppearance;
@property(nonatomic, assign) UIModalTransitionStyle modalTransitionStyle;

- (void)viewDidLoad;
- (void)viewWillAppear:(BOOL)animated;
- (void)viewDidAppear:(BOOL)animated;
- (void)viewWillDisappear:(BOOL)animated;
- (void)viewDidDisappear:(BOOL)animated;

@end

Important Elements

Element	Meaning
@interface	Class definition
@property	Property (public interface)
- (type)	Instance method
+ (type)	Class method
(nonatomic, assign)	Property attributes
@protocol	Protocol/interface requirement

Advanced Usage

Filtering and Finding

# Extract specific class
class-dump /path/to/binary | grep "class.*UIViewController"

# Find methods
class-dump /path/to/binary | grep "viewDidLoad"

# Find private methods
class-dump /path/to/binary | grep "_"

# Count classes
class-dump /path/to/binary | grep "^@interface" | wc -l

Architecture-Specific Extraction

# List available architectures
lipo -info /path/to/binary

# Extract specific architecture
class-dump --arch arm64 /path/to/binary > headers.h
class-dump --arch x86_64 /path/to/binary > headers_sim.h

# Extract universal binary (all architectures)
class-dump /path/to/binary > all_headers.h

Runtime Information

# Include runtime information
class-dump -r /path/to/binary

# Show instance variable offsets
class-dump --show-ivar-offset /path/to/binary

# Detailed output
class-dump --show-superclass --show-ivar-offset /path/to/binary

Analyzing Extracted Headers

Class Hierarchy

# Extract and analyze class structure
class-dump -H /path/to/app.app/app -o headers/

# Find all subclasses of UIViewController
grep -r "UIViewController" headers/ | grep "^@interface"

# Show inheritance chain
awk '/@interface/ {print}' headers/*.h | sort

Method Analysis

# Find all delegates
grep -r "Delegate" headers/ | grep "@protocol"

# Find all callbacks
grep -r "Block\|Handler\|Callback" headers/

# Find all notification handlers
grep -r "notification" headers/

Property Analysis

# Find all properties
grep -r "@property" headers/ | head -20

# Properties with custom setters
grep -r "@property.*custom" headers/

# Properties that are weak references
grep -r "@property.*weak" headers/

Practical Workflows

Reverse Engineer an App

# Step 1: Extract headers
class-dump -H MyApp.app/MyApp -o myapp_headers/

# Step 2: Extract frameworks
class-dump -H MyApp.app/Frameworks/MyFramework.framework/MyFramework \
    -o myframework_headers/

# Step 3: Analyze class structure
grep "^@interface" myapp_headers/*.h

# Step 4: Find interesting methods
grep -r "login\|auth\|password\|decrypt" myapp_headers/

# Step 5: Look at properties
grep -r "@property" myapp_headers/ | grep -i "secret\|token\|key"

# Step 6: Document findings
cat myapp_headers/MyAppViewController.h

Finding API Keys and Secrets

# Extract headers
class-dump -H /path/to/app.app/app -o headers/

# Search for suspicious method names
grep -r "key\|secret\|token\|api\|password" headers/ | head -20

# Look for constants in class definitions
grep -r "NSURL\|URLWithString\|baseURL" headers/

# Check initialization methods
grep -r "initWith\|init" headers/ | head -20

Understanding Custom Classes

# Extract
class-dump -H MyApp.app/MyApp -o headers/

# Find custom classes (not Apple)
find headers -name "*.h" -exec grep -l "^@interface [A-Z][a-z]" {} \;

# Show dependencies
grep "@interface.*:" headers/*.h | grep -v "NS\|UI"

# Trace class structure
cat headers/MyCustomClass.h
cat headers/MyCustomClassDelegate.h

Dealing with Common Issues

Permission Denied

# Run with sudo if needed
sudo class-dump /System/Library/Frameworks/UIKit.framework/UIKit

# Check file permissions
ls -la /path/to/binary

# May need to codesign or disable SIP on newer macOS

Architecture Mismatch

# Check your arch
arch                   # x86_64, arm64, etc

# See available archs
lipo -info /path/to/binary

# Extract matching arch explicitly
class-dump --arch x86_64 /path/to/binary

Encrypted Binaries

# App Store binaries are encrypted
# Must dump from running process or use unencrypted version

# Option 1: Use debugger to dump from memory
# Option 2: Use Enterprise/Development build
# Option 3: Use jtool or Frida to extract

Combining with Other Tools

With IDA Pro

# Export headers from class-dump
class-dump -H app.app/app -o headers/

# Import into IDA as type info
# File > Type Information > Parse C Header File
# Select generated header files

With Hopper

# Hopper integrates with class-dump
# Tools > Objective-C Class Dump
# Automatically shows class info alongside disassembly

With Ghidra

# No direct integration
# But can cross-reference class-dump output with Ghidra analysis
# Create symbol mappings manually

Tips and Best Practices

• Always extract from the correct architecture (arm64 for device, x86_64 for simulator)
• Save headers to organized directory structure for large apps
• Use grep and awk to search across multiple header files
• Document interesting findings as you analyze
• Compare headers across app versions to find new functionality
• Look for private methods (starting with underscore) for hidden functionality
• Check @protocol definitions for expected behavior
• Cross-reference with debugger output for validation
• Use symbolic execution when available for deeper analysis

Resources

• class-dump GitHub: https://github.com/nygard/class-dump
• Official Site: http://steqart.io/cdn/class-dump/
• Objective-C Runtime Reference: https://developer.apple.com/reference/objectivec/
• iOS App Reverse Engineering Guide

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Last updated: 2026-03-30