sojorn/zero_knowledge_backup_summary.md

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).