# Backup & Recovery

LSPV uses a 24-word BIP-39 mnemonic phrase as the encryption key for backup files. The mnemonic is generated when you create a vault and shown **once** — LSPV never stores it on disk.

## Why BIP-39?

- 256 bits of entropy from a standardized, human-verifiable wordlist
- Easy to write down on paper without transcription errors
- Widely understood — no proprietary format
- The same mnemonic can regenerate the backup key deterministically

## Backup File Format (.vbk)

```
lspv_backup_YYYY-MM-DD_XXXXXXXX.vbk
├── Header: magic bytes b"LSPV_BACKUP_V2"
├── KDF params: Argon2id (m=4GB, t=10, p=4) + random salt
├── Encrypted payload (XChaCha20-Poly1305):
│   ├── Vault UUID
│   ├── Created timestamp
│   ├── Schema version
│   ├── BLAKE3 checksum of vault.db
│   └── Full vault.db bytes
```

**Key derivation for backup** uses much stronger Argon2id parameters than normal unlock (4 GB RAM vs 256 MB, 10 iterations vs 4). This is intentional: backup files may be stored on USB drives or cloud storage, so brute-forcing the mnemonic must be computationally infeasible even with large GPU farms.

## Export a Backup

Go to **Settings → Backup**:

1. Click **Generate Phrase** — LSPV generates 24 BIP-39 words
2. Write them on paper. LSPV never saves the mnemonic to disk.
3. Tick **"I have written these words on paper"**
4. Optional: click **Verify** to spot-check 3 random words (recommended)
5. Click **Export .vbk** → choose your save location

A timestamped auto-copy is also saved to `app_data/backups/lspv_{timestamp}.vbk`.  
The 7 most recent auto-copies are kept automatically.

## Restore from Backup

Go to **Settings → Backup → Restore**:

1. Paste your 24-word mnemonic phrase (space-separated)
2. Click **Choose .vbk file** → select the backup file
3. Click **Choose destination folder** → where the restored vault will be placed
4. Click **Restore**

LSPV validates the BIP-39 phrase before attempting decryption, then verifies the BLAKE3 integrity checksum after decryption. A tampered or corrupted file is rejected before any data is written.

LSPV verifies the BLAKE3 checksum inside the ciphertext after decryption. If the file was corrupted or tampered with, restoration fails with an integrity error — it will not silently restore a broken vault.

## Recommended Backup Strategy (3-2-1)

| Copy | Location | Notes |
|------|----------|-------|
| 1 | Local drive | Auto-saved on each manual export (7 copies, `app_data/backups/`) |
| 2 | USB flash drive | Offline copy, update weekly |
| 3 | Second computer or NAS | LAN-accessible, no cloud |

Never store the mnemonic in the same physical location as the backup file. If an attacker finds both, they can decrypt the backup.

## Mnemonic Safety

- Write the 24 words on paper with a permanent marker
- Store the paper in a fireproof safe or safety deposit box
- Consider splitting: give 12 words to a trusted person and keep 12 yourself (requires both to restore)
- Never photograph the mnemonic with your phone — photos sync to cloud
- Never type it into any website or app other than LSPV

## Version Compatibility

| Format | Supported |
|--------|-----------|
| v1 (XChaCha20 + Argon2id 256 MB) | ✅ read + write |
| v2 (XChaCha20 + Argon2id 4 GB + BLAKE3) | ✅ read + write |