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Security Policy

Overview

ModSwitchIME is designed with privacy and security as core principles. This document outlines our security measures and what data the application can access.

What ModSwitchIME Can Access

✅ Allowed Access

  • Modifier key presses only (Command ⌘, Shift ⇧, Control ⌃, Option ⌥)
  • Input method switching via macOS Text Input Source APIs
  • User preferences stored locally in UserDefaults

❌ No Access To

  • Regular keystrokes or typing content - The app only monitors modifier keys
  • Clipboard contents - No clipboard access is requested or used
  • Screen contents - No screen recording or capture
  • Network communication - No network capabilities
  • File system - No file system access except preferences
  • Personal data - No collection of user data or telemetry

Security Measures

1. Minimal Permissions

  • Only requests Accessibility permission for modifier key detection
  • Limited entitlements for input method functionality and system integration
  • Event monitoring limited to flagsChanged events only
  • Read-only file access for user-selected files (system integration)

2. Privacy Protection

  • No keylogging: Regular keystrokes are never captured
  • Immediate data disposal: Event data is cleared from memory after processing
  • No data persistence: No logs or records of key presses are stored
  • Local processing only: All operations happen on your Mac

3. Open Source Transparency

  • Complete source code available for inspection
  • Build instructions provided for self-compilation
  • Regular security updates and community review

4. Code Signing & Notarization

  • Production builds: Signed with Developer ID certificate
  • Development builds: Ad-hoc signed for local development
  • Notarized by Apple for additional security verification (production only)
  • Hardened Runtime enabled

Accessibility Permission

ModSwitchIME requires Accessibility permission to monitor modifier key events. This permission allows the app to:

  • Detect when modifier keys are pressed and released
  • Distinguish between left and right modifier keys
  • Measure key press duration for combination detection

You can revoke this permission at any time:

  1. Open System Settings
  2. Go to Privacy & Security → Accessibility
  3. Uncheck ModSwitchIME

Security Best Practices for Users

  1. Download from official sources only

    • GitHub Releases: https://github.com/nissy/ModSwitchIME/releases
    • Verify code signature: codesign -dv --verbose=4 /Applications/ModSwitchIME.app
    • Production builds should show: Authority=Developer ID Application: Yoshihiko Nishida (R7LKF73J2W)

  2. Review permissions

    • Only grant Accessibility permission
    • No additional permissions should be requested

  3. Monitor system resources

    • CPU usage should be minimal (<0.1% when idle)
    • Memory usage should be under 25MB

Reporting Security Issues

If you discover a security vulnerability, please report it responsibly:

  1. Do not create a public GitHub issue
  2. Email: [Contact repository owner via GitHub]
  3. Include:
    • Description of the vulnerability
    • Steps to reproduce
    • Potential impact
    • Suggested fix (if any)

Security Audit Trail

Latest Security Review

  • Date: 2025-06-20
  • Version: 1.0.0
  • Changes:
    • Confirmed flagsChanged-only event monitoring for enhanced privacy
    • Verified immediate event data disposal implementation
    • Enhanced user privacy notifications
    • Updated security documentation with actual implementation details
    • Verified minimal entitlements configuration

Security Checklist

  • Minimal permission model
  • No network capabilities
  • No file system access beyond preferences
  • No data collection or telemetry
  • Signed and notarized builds
  • Open source for transparency
  • Regular security updates

Privacy Compliance

ModSwitchIME is designed to comply with:

  • macOS privacy guidelines
  • GDPR principles (no personal data collection)
  • California Consumer Privacy Act (CCPA)

Version History

Version Date Security Changes
1.0.0 2025-06-20 Enhanced privacy protections, removed keyDown monitoring

This security policy is subject to updates. Please check the latest version in the repository.