# Zero Knowledge Cloud Backup - Implementation Summary

## Status: COMPLETE & DEPLOYED ✅

### 1. Security Architecture (Zero Knowledge)
- **Principle**: The server never sees your private keys.
- **Cloud Backups**: Default to **Messages Only**. The payload contains encrypted message history but explicitly excludes the key pairs needed to decrypt them.
- **Local Backups**: Must be used to backup **Keys + Messages**. This is the only way to restore your identity (Subjective Identity).
- **Encryption**: All data is encrypted client-side using Argon2id (password derivation) and AES-GCM (content encryption) before leaving the device.

### 2. Frontend Implementation (Flutter)
- **Service**: Rebuilt `LocalKeyBackupService.dart` to handle the dual-mode backup logic.
- **UI**: 
  - Added toggle for "Cloud" vs "Local" backup.
  - "Secure Mode" indicator when uploading to cloud (confirming keys are excluded).
  - Explicit warning: "NOT RECOMMENDED for cloud backups. Keep keys local."

### 3. Backend Implementation (Go)
- **Endpoints**: `POST /backups/upload` and `GET /backups/download` are active.
- **Storage**: Stores opaque `encrypted_blob`, `salt`, `nonce`, and `mac`.
- **Database**: 
  - Applied migration `000003_e2ee_backup_recovery`.
  - Created tables: `cloud_backups`, `backup_preferences`, `user_devices`.

### 4. Deployment Details
- **Server**: `194.238.28.122`
- **Service**: `sojorn-api` (Restarted at ~01:55 server time)
- **Database**: Migrations applied successfully via `migrate-linux` tool.

### 5. How to Test
1. **Create Identity Backup**: Go to "Full Backup & Recovery" -> Select "Local File" -> "Export Backup". Save this file safely!
2. **Cloud Upload**: Switch to "Cloud Backup" -> Encrypt with password -> "Upload Backup".
3. **Restore Flow**:
   - Wipe app / New Device.
   - **Step 1**: "Import Backup" using your Local File (Restores Identity/Keys).
   - **Step 2**: "Download & Restore" from Cloud (Restores Message History).
