📱 Inqrypt — Ultra-Private QR-Encrypted Notes App

Inqrypt is a fully offline app with hierarchical encryption, allowing users to create encrypted notes (with images) and store them as QR codes. The app uses biometric protection, supports localization, haptic feedback, and does not store any data in the cloud or on servers.

🎯 Core Mission & Principles

Security Principles:

• 🔐 Hierarchical Encryption: Master Key → Note Keys → Note Content + Images
• 📱 Biometric Protection: Face ID / Touch ID to access master key
• 🚫 Fully Offline: No network calls or cloud storage
• 🗑️ No History: Notes are never stored in plain form
• 🔑 Unique Keys: Each note has its own encryption key
• 🖼️ Encrypted Images: Images are encrypted alongside text
• 🌍 Multilingual Support: English and Russian supported
• 📳 Haptic Feedback: UX improved with vibration response

Security Architecture:

Master Key (M) ─▶ Encrypted Note Key (Kₙ) ─▶ Encrypted Note Content ─▶ Encrypted Images
      │                   │                        │                      │
      ▼                   ▼                        ▼                      ▼
Secure Storage       QR Code (Kₙ)         File System            File System

🧩 Features

Feature	Status	Description
✅ Create Notes	Done	Apple Notes-style editor with titles and content
✅ Add Images	Done	Encrypted images from gallery/camera
✅ Hierarchical Encryption	Done	M → Kₙ → Content + Images with [MAGIC]:: signature
✅ Biometric Unlock	Done	Face ID / Touch ID unlock for Master Key
✅ QR Code Generation	Done	Only encrypted Kₙ is in QR
✅ QR Code Scanning	Done	Find note by decrypted Kₙ
✅ Note Editing	Done	Edit and re-encrypt notes
✅ Image Gallery	Done	Fullscreen viewing and deletion
✅ Secure Storage	Done	flutter_secure_storage + filesystem
✅ Note Deletion	Done	Biometrically protected mass delete
✅ Share/Copy	Done	Share QR and content
✅ Save QR to Gallery	Done	Export QR as image
✅ Flutter Quill Editor	Done	Rich editor with images
✅ Localization	Done	English and Russian
✅ Vibration System	Done	Haptic UX for all actions
✅ Navigation Feedback	Done	Vibrates on navigation
✅ Notifications	Done	Vibrating notifications
✅ Scan Animation	Done	Fast checkmark animation
✅ Demo Mode	Done	Isolated App Store review mode

🎭 Demo Mode

Purpose:

Demo Mode exists to showcase full functionality without requiring biometric setup or encryption during App Store review.

Flow Overview:

Main Screen ─▶ Demo Note ─▶ Mock QR Scanner ─▶ Demo View Page

Key Elements:

• Blue Demo Button on main screen (replaces Security Status widget)
• Pre-filled Editable Note using QuillNoteEditor
• Fake Encryption using constant mock QR
• Mock Scanner with simulated animation
• Demo View Page mimicking real app UX
• All localized, full isolation from actual data

🔐 Encryption Architecture

1. Master Key (M)

• 32 bytes random
• Encrypted with biometric hash
• Stored via flutter_secure_storage
• Access via Face ID / Touch ID

2. Note Keys (Kₙ)

• 32 bytes per note
• AES-256-CBC encrypted using Master Key
• Stored in QR as: base64(iv):base64(cipher)

3. Note Content

• Begins with [MAGIC]::
• AES-256-CBC with Note Key
• Stored in device filesystem
• Quill Delta format for rich content

4. Images

• Compressed to max 1920x1920, JPEG/PNG
• Encrypted with Note Key (AES-256-CBC)
• Stored in encrypted folder
• Integrated into Quill via embeds

5. Encryption Flow

Create Note:
  Content + Images → [MAGIC]:: → Encrypt(Kₙ) → Encrypt(M) → Export QR

Scan QR:
  QR → Decrypt(M) → Decrypt(Kₙ) → Find note by signature → Decrypt images

Edit Note:
  Decrypt → Edit → Re-encrypt → Update note

💻 Tech Stack

Component	Tech
UI	Flutter 3.8+
UI Theme	Material 3 (Dark)
Editor	Flutter Quill 11.4.2
Encryption	encrypt 5.0.3 (AES-256-CBC)
Hashing	crypto 3.0.3 (SHA-256)
Secure Storage	flutter_secure_storage (Keychain/Keystore)
Biometric Auth	local_auth
QR Code	mobile_scanner
Image Picker	image_picker
Haptics	vibration
Localization	flutter_localizations

🎨 UX Highlights

• Apple Notes-style input with auto-title from first line
• Quill toolbar above keyboard
• Encrypted QR generation at bottom right
• Full gallery view with swipe/zoom/delete
• Fast animations, haptic feedback, and smooth transitions

📊 Project Stats

• Security Level: HIGH
• Encryption: AES-256-CBC
• Master Key Storage: Secure + Biometric
• Supported Platforms: iOS
• Languages: English, Russian
• Status: Production-ready

☕ Support the Project

Inqrypt is free, open-source, and offline by design. If you value privacy-first tools, consider supporting development:

🔗 buymeacoffee.com/supportqlt

📫 Contact: support@inqrypt.com
🌐 Website: inqrypt.com

📄 License

This project is licensed under the MIT License — you're free to use, modify, and distribute it with proper attribution.