added encryption

project-context.md

@@ -107,28 +107,66 @@ _Last updated: 2026-03-04_
 - Entry filtering by date
 - Pagination support
 
-### Frontend-Backend Integration (Completed)
+### Zero-Knowledge Encryption Implementation (Completed)
 
-✅ **API Service Layer** — Created `src/lib/api.ts` with all backend calls
-✅ **AuthContext Updated** — Now syncs users with MongoDB on login
+✅ **Crypto Module** — Created `src/lib/crypto.ts` with complete zero-knowledge privacy
 
-- Auto-registers new users in MongoDB
-- Fetches existing user profiles
-- Provides `userId` (MongoDB ID) to all pages
-  ✅ **HomePage** — Entry creation via POST `/api/entries/{userId}`
-- Save with success/error feedback
-- Clears form after save
-  ✅ **HistoryPage** — Fetches entries via GET `/api/entries/{userId}`
-- Calendar shows days with entries
-- Lists recent entries with timestamps
-- Filters by current month
-  ✅ **SettingsPage** — Updates user settings via PUT `/api/users/update/{userId}`
-- Theme selector (light/dark) with MongoDB persistence
-- Profile info from Firebase
+- Libsodium.js integrated for cryptography (XSalsa20-Poly1305)
+- Key derivation from Firebase credentials using Argon2i KDF
+- Device key generation and localStorage persistence
+- Encrypted secret key storage in IndexedDB
+- Entry encryption/decryption utilities
+
+✅ **Key Management Flow**
+
+- **Login:** KDF derives master key from `firebaseUID + firebaseIDToken + salt`
+- **Device Setup:** Random device key generated, stored in localStorage
+- **Key Cache:** Master key encrypted with device key → IndexedDB
+- **Memory:** Master key kept in memory during session only
+- **Subsequent Login:** Cached encrypted key recovered via device key
+- **New Device:** Full KDF derivation, new device key generated
+- **Logout:** Master key cleared from memory; device key persists for next session
+
+✅ **AuthContext Enhanced**
+
+- Added `secretKey` state (in-memory only)
+- Integrated encryption initialization on login
+- Device key and IndexedDB cache management
+- Automatic recovery of cached keys on same device
+
+✅ **Backend Models Updated** — Zero-knowledge storage
+
+- `JournalEntryCreate`: title/content optional (null if encrypted)
+- `EncryptionMetadata`: stores ciphertext, nonce, algorithm
+- Server stores **encryption metadata only**, never plaintext
+- All entries encrypted with XSalsa20-Poly1305 (libsodium)
+
+✅ **API Routes** — Encrypted entry flow
+
+- POST `/api/entries/{userId}` accepts encrypted entries
+- Validation ensures ciphertext and nonce present
+- Entry retrieval returns full encryption metadata
+- Update routes support re-encryption
+- Server processes only encrypted data
+
+✅ **HomePage** — Encrypted entry creation
+
+- Entry and title combined: `title\n\n{entry}`
+- Encrypted with master key before transmission
+- Sends ciphertext, nonce, algorithm metadata to backend
+- Success feedback confirms secure storage
+
+✅ **HistoryPage** — Entry decryption & display
+
+- Fetches encrypted entries from server
+- Client-side decryption with master key
+- Splits decrypted content: first line = title
+- Graceful handling of decryption failures
+- Displays original title or `[Encrypted]` on error
 
 ### Next Steps (Implementation)
 
-🔄 Add entry detail view / edit functionality  
-🔄 Firebase token verification in backend middleware  
-🔄 Search/filter entries by date range  
-🔄 Client-side encryption for entries
+🔄 Entry detail view with full decryption  
+🔄 Edit encrypted entries (re-encrypt on changes)  
+🔄 Search/filter encrypted entries (client-side only)  
+🔄 Export/backup encrypted entries with device key