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QryptChat - Quantum-Resistant Chat Application Architecture

Overview

QryptChat is a quantum-resistant, end-to-end encrypted messaging application built as a Progressive Web App (PWA) using SvelteKit 5, Supabase Cloud, and post-quantum cryptography.

Technology Stack

Frontend

  • Framework: SvelteKit (latest) with Svelte 5
  • Styling: Vanilla CSS with CSS Grid/Flexbox
  • PWA: Service Worker + Web App Manifest
  • Real-time: Native WebSockets
  • Build Tool: Vite (included with SvelteKit)

Backend

  • Database: Supabase Cloud (PostgreSQL)
  • Authentication: Supabase Auth + Twilio SMS
  • Real-time: Supabase Realtime + WebSocket fallback
  • File Storage: Supabase Storage (for media)
  • Edge Functions: Supabase Edge Functions (Deno)

Cryptography

  • Key Exchange: CRYSTALS-Kyber (NIST PQC standard)
  • Digital Signatures: CRYSTALS-Dilithium (NIST PQC standard)
  • Symmetric Encryption: ChaCha20-Poly1305 (for message content)
  • Key Derivation: HKDF with SHA-256
  • Random Generation: Web Crypto API

System Architecture

graph TB
    Client[SvelteKit PWA Client]
    SW[Service Worker]
    WS[WebSocket Connection]
    
    subgraph Supabase Cloud
        Auth[Supabase Auth]
        DB[(PostgreSQL Database)]
        RT[Realtime Engine]
        Storage[File Storage]
        Edge[Edge Functions]
    end
    
    subgraph External Services
        Twilio[Twilio SMS API]
    end
    
    Client --> SW
    Client --> WS
    WS --> RT
    Client --> Auth
    Client --> DB
    Client --> Storage
    Auth --> Twilio
    Edge --> DB
    RT --> DB
Loading

Database Schema

Core Tables

  • users: User profiles and public keys
  • conversations: Chat conversations (1:1 and groups)
  • messages: Encrypted message storage
  • conversation_participants: Many-to-many relationship
  • contacts: User contact relationships
  • device_keys: Per-device key pairs for multi-device support

Security Tables

  • key_bundles: Pre-keys for new conversations
  • message_keys: Ephemeral keys for forward secrecy
  • verification_codes: SMS verification storage

Security Model

Key Management

  1. Identity Keys: Long-term CRYSTALS-Dilithium key pairs per user
  2. Ephemeral Keys: CRYSTALS-Kyber key pairs for each conversation
  3. Message Keys: ChaCha20 keys derived from shared secrets
  4. Forward Secrecy: Keys rotated regularly, old keys deleted

Message Flow

  1. Client generates ephemeral key pair
  2. Key exchange using CRYSTALS-Kyber
  3. Derive symmetric key using HKDF
  4. Encrypt message with ChaCha20-Poly1305
  5. Sign with CRYSTALS-Dilithium
  6. Store encrypted in database

PWA Features

  • Offline Support: Service Worker caches for offline messaging
  • Push Notifications: Web Push API for message alerts
  • Install Prompt: Add to home screen functionality
  • Background Sync: Queue messages when offline

Real-time Communication

  • Primary: Supabase Realtime for message delivery
  • Fallback: Direct WebSocket connection
  • Presence: Online/offline status tracking
  • Typing Indicators: Real-time typing status

Contact Management

  • Phone Verification: Twilio SMS OTP
  • Contact Discovery: Hash-based phone number matching
  • Privacy: No plaintext phone numbers stored
  • Invitations: SMS invites to non-users

Group Features

  • Max Size: 100 participants
  • Admin Roles: Creator, admin, member hierarchy
  • Permissions: Message, add members, change settings
  • Group Keys: Shared group encryption keys
  • Member Management: Add/remove with proper key rotation

Performance Considerations

  • Lazy Loading: Messages loaded on demand
  • Virtual Scrolling: Efficient large conversation rendering
  • Image Optimization: WebP format with compression
  • Bundle Splitting: Code splitting for optimal loading
  • CDN: Supabase CDN for global performance

Deployment Architecture

  • Frontend: Static hosting via Supabase or Vercel
  • Database: Supabase Cloud (multi-region)
  • Edge Functions: Deployed to Supabase Edge Runtime
  • Monitoring: Supabase Analytics + custom metrics