# Database encryption at rest

> Status: Complete (awaiting production deployment)
> Tier: 2 (Security / Infrastructure)

## Goal

The entire Berrypod shop is a single encrypted SQLite file. Portable, private, encrypted. Copy the file, set your encryption key, and host anywhere.

## Why

1. **True encryption at rest** — not just sensitive fields, the entire database
2. **Safe backups** — can store backup files anywhere without additional encryption
3. **Simple migration** — copy file + set env var = working shop on new server
4. **Privacy by design** — even if someone gets the file, data is protected

## Current state

- Standard SQLite 3.51.1 (no encryption)
- Sensitive fields (API keys, TOTP secrets) encrypted with Cloak.Ecto using `SECRET_KEY_BASE`
- exqlite 0.34.0 compiled without SQLCipher

## Target state

- SQLCipher-encrypted database file
- Encryption key via `SECRET_KEY_DB` environment variable
- Existing Cloak encryption remains (defence in depth for secrets)
- Safe backup via `VACUUM INTO` works on encrypted database
- Admin backup page with database stats and restore

---

## Security model

Two independent secrets, defence in depth:

| Secret | Purpose | Protects against |
|--------|---------|------------------|
| `SECRET_KEY_BASE` | Phoenix sessions, Cloak field encryption | SQL access without app secret |
| `SECRET_KEY_DB` | SQLCipher whole-database encryption | File access without DB key |

Both are required for production. If one is compromised, the other layer still protects.

**SQLCipher spec:**
- AES-256 in CBC mode
- HMAC-SHA512 per page (tamper detection)
- PBKDF2 key derivation (256,000 iterations)
- Each page independently encrypted

---

## Implementation

### Phase 1: Install SQLCipher and recompile exqlite

**Dev machine (Debian/Ubuntu):**
```bash
# Debian bookworm: use backports for SQLCipher 4.6.1 (stable has 3.4.1 which is too old)
sudo apt install -t bookworm-backports libsqlcipher-dev

# Ubuntu 24.04+: standard repos have a recent enough version
sudo apt install libsqlcipher-dev
```

**Dev machine (macOS):**
```bash
brew install sqlcipher
```

**Set build environment and recompile:**
```bash
# Tell exqlite to use system SQLCipher instead of bundled SQLite
export EXQLITE_USE_SYSTEM=1
export EXQLITE_SYSTEM_CFLAGS="-I/usr/include/sqlcipher"
export EXQLITE_SYSTEM_LDFLAGS="-lsqlcipher"

# Force recompile
mix deps.clean exqlite --build
mix deps.compile exqlite
```

**Verify SQLCipher is active:**
```elixir
{:ok, conn} = Exqlite.Basic.open(":memory:")
{:ok, _q, result, _c} = Exqlite.Basic.exec(conn, "PRAGMA cipher_version;")
# Should return [["4.x.x"]] — if empty, SQLCipher not linked
```

### Phase 2: Configure encryption key

**Generate keys:**
```bash
mix phx.gen.secret  # → SECRET_KEY_BASE
mix phx.gen.secret  # → SECRET_KEY_DB
```

**Configure exqlite (runtime.exs):**
```elixir
# config/runtime.exs

# Database encryption (optional for dev, required for production)
db_key = System.get_env("SECRET_KEY_DB")

config :berrypod, Berrypod.Repo,
  database: database_path,
  key: db_key  # nil = unencrypted, string = SQLCipher encryption
```

The `:key` option is native to exqlite — it handles the `PRAGMA key` automatically on connection.

**Dev mode:** No `SECRET_KEY_DB` set = unencrypted database (easier local development).

**Production mode:** `SECRET_KEY_DB` required = encrypted database.

### Phase 3: Fresh database with encryption

Since we're starting fresh (no migration needed):

```bash
# Delete old unencrypted database
rm berrypod_dev.db berrypod_dev.db-shm berrypod_dev.db-wal

# Start with encryption enabled
SECRET_KEY_DB="$(mix phx.gen.secret)" mix ecto.create
SECRET_KEY_DB="your-key" mix ecto.migrate
SECRET_KEY_DB="your-key" mix phx.server
```

### Phase 4: Fly.io deployment

**Update Dockerfile:**
```dockerfile
# Install SQLCipher
RUN apt-get update -y && \
    apt-get install -y libsqlcipher-dev && \
    apt-get clean && rm -rf /var/lib/apt/lists/*

# Build exqlite with system SQLCipher
ENV EXQLITE_USE_SYSTEM=1
ENV EXQLITE_SYSTEM_CFLAGS="-I/usr/include/sqlcipher"
ENV EXQLITE_SYSTEM_LDFLAGS="-lsqlcipher"
```

**Set the secret:**
```bash
fly secrets set SECRET_KEY_DB="$(mix phx.gen.secret)"
```

**Deploy:**
```bash
fly deploy
```

---

## Admin backup page

Route: `/admin/backup`

### Database stats display

Show useful context before backup/restore:

**Overview section:**
- Total database size (formatted: "12.3 MB")
- Encryption status (SQLCipher version or "Unencrypted")
- Database created date
- Last backup date (if tracked)

**Table breakdown:**

| Table | Rows | Size |
|-------|------|------|
| products | 16 | 45 KB |
| product_variants | 142 | 28 KB |
| product_images | 89 | 12 KB |
| orders | 23 | 18 KB |
| images | 156 | 8.2 MB |
| settings | 42 | 4 KB |
| ... | | |

**Key counts:**
- Products: 16
- Orders: 23
- Media files: 156
- Newsletter subscribers: 89

**Queries for stats:**
```sql
-- Total database size
SELECT page_count * page_size as size
FROM pragma_page_count(), pragma_page_size();

-- Row counts per table
SELECT name FROM sqlite_master WHERE type='table' AND name NOT LIKE 'sqlite_%';
-- Then COUNT(*) each

-- Table sizes (via dbstat virtual table)
SELECT name, SUM(pgsize) as size
FROM dbstat
GROUP BY name
ORDER BY size DESC;

-- SQLCipher version
PRAGMA cipher_version;
```

### Download backup

Use SQLite's `VACUUM INTO` for a safe, consistent backup:

```elixir
def create_backup do
  timestamp = DateTime.utc_now() |> Calendar.strftime("%Y%m%d-%H%M%S")
  backup_path = Path.join(System.tmp_dir!(), "berrypod-backup-#{timestamp}.db")

  Ecto.Adapters.SQL.query!(Repo, "VACUUM INTO ?", [backup_path])

  {:ok, backup_path}
end
```

The backup file is encrypted with the same key — portable to any server with that key.

**UI:**
- "Download backup" button
- Shows estimated file size
- Filename: `berrypod-backup-YYYYMMDD-HHMMSS.db`

### Restore backup

1. Upload encrypted backup file
2. Validate it opens with the current key
3. Show comparison: current vs uploaded (row counts, size)
4. Confirm with explicit action ("Replace current database")
5. Stop accepting requests (maintenance mode)
6. Replace database file
7. Restart application

**UI:**
- File upload dropzone
- Validation feedback (valid/invalid/wrong key)
- Side-by-side comparison before restore
- Confirmation modal with warnings

---

## Task breakdown

| # | Task | Est | Notes |
|---|------|-----|-------|
| 1 | ~~Install SQLCipher on dev machine~~ | ✓ | `apt install -t bookworm-backports libsqlcipher-dev` (4.6.1) |
| 2 | ~~Set build flags, recompile exqlite~~ | ✓ | Env vars, `mix deps.clean/compile` |
| 3 | ~~Verify SQLCipher with `PRAGMA cipher_version`~~ | ✓ | Returns "4.6.1 community" |
| 4 | ~~Add `:key` config to runtime.exs~~ | ✓ | Required in prod, optional in dev |
| 5 | ~~Test fresh encrypted database~~ | ✓ | Verified encryption works |
| 6 | ~~Update Dockerfile for Fly.io~~ | ✓ | Install package, set build flags |
| 7 | Deploy encrypted to Fly.io | 15m | Set secret, deploy, verify |
| 8 | ~~Database stats context module~~ | ✓ | `Berrypod.Backup` with sizes, counts, encryption status |
| 9 | ~~Admin backup page — stats display~~ | ✓ | `/admin/backup` LiveView |
| 10 | ~~Admin backup page — download~~ | ✓ | VACUUM INTO, JS download hook |
| 11 | ~~Admin backup page — restore upload~~ | ✓ | Upload, validation, comparison |
| 12 | ~~Admin backup page — restore action~~ | ✓ | Maintenance mode, swap, restart |
| 13 | ~~Update README with key management~~ | ✓ | Document backup procedures |

**Total: ~8-9 hours**

---

## Security notes

- **Key length:** 256-bit minimum. `mix phx.gen.secret` produces 512-bit which is fine.
- **Key storage:** Environment variables only. Never commit to code.
- **Key rotation:** Requires re-encrypting entire database. Rare operation.
- **Lost key = lost data:** No recovery possible. Document key backup procedures clearly.
- **Defence in depth:** Keep Cloak encryption for API keys even with DB encryption.

---

## Dev workflow

For convenience, add to `.envrc` (direnv) or shell profile:

```bash
# Build flags (needed once per machine after installing SQLCipher)
export EXQLITE_USE_SYSTEM=1
export EXQLITE_SYSTEM_CFLAGS="-I/usr/include/sqlcipher"
export EXQLITE_SYSTEM_LDFLAGS="-lsqlcipher"

# Optional: dev database encryption (or omit for unencrypted dev)
# export SECRET_KEY_DB="dev-only-key-not-for-production"
```

### Encrypted dev database

If you want to test encryption locally:

```bash
export SECRET_KEY_DB="dev-test-key-12345"
mix ecto.reset  # recreates with encryption
mix phx.server
```

### Unencrypted dev database

For simpler local development, just don't set `SECRET_KEY_DB`. The database will be unencrypted but otherwise identical.

---

## Compatibility

- **Litestream:** Works with SQLCipher. Replicates encrypted bytes to S3.
- **sqlite3 CLI:** Use `sqlcipher` CLI to open encrypted databases.
- **DB Browser for SQLite:** Supports SQLCipher — enter key when opening.
- **Tests:** Run unencrypted (faster) unless specifically testing encryption.

---

## Verification checklist

After implementation, verify:

```bash
# 1. SQLCipher is linked
mix run -e '{:ok, c} = Exqlite.Basic.open(":memory:"); {:ok, _, r, _} = Exqlite.Basic.exec(c, "PRAGMA cipher_version;"); IO.inspect(r.rows)'
# Should print [["4.x.x"]]

# 2. Encrypted database is unreadable without key
file berrypod_prod.db
# Should show "data" not "SQLite 3.x database"

# 3. Encrypted database opens with key
SECRET_KEY_DB="your-key" mix run -e 'Berrypod.Repo.query!("SELECT 1")'
# Should succeed

# 4. Encrypted database fails without key
mix run -e 'Berrypod.Repo.query!("SELECT 1")'
# Should fail with "file is not a database"
```

---

## Files to modify

| File | Change |
|------|--------|
| `config/runtime.exs` | Add `:key` option to Repo config |
| `Dockerfile` | Install SQLCipher, set build env vars |
| `fly.toml` | (no change, key via secrets) |
| `lib/berrypod/backup.ex` | New — backup/restore context |
| `lib/berrypod_web/live/admin/backup_live.ex` | New — backup admin page |
| `lib/berrypod_web/router.ex` | Add `/admin/backup` route |
| `README.md` | Document key management |