security: encrypt synchronized unfiled drafts (Closes #1098)

tests/test_private_state.py

@@ -84,7 +84,7 @@ def test_private_sqlite_connection_rejects_a_symlink_before_opening_target(tmp_p
         TodayStore,
         LaterStore,
         SavedSearchStore,
-        UnfiledDraftStore,
+        lambda path: UnfiledDraftStore(path, encryption_key=b"d" * 32),
         CompletedFiledReviewStore,
         PushSubscriptionStore,
         LiveSnapshotStore,

tests/test_unfiled_draft_store.py

@@ -1,10 +1,16 @@
+import json
+import sqlite3
+
 import httpx
 import pytest
 
-from src import main
+from src import main, unfiled_draft_store
 from src.unfiled_draft_store import UnfiledDraftConflict, UnfiledDraftStore
 
 
+ENCRYPTION_KEY = b"d" * 32
+
+
 def draft(draft_id="phone-capture", *, title="Broken checkout", evidence=None):
     return {
         "id": draft_id,
@@ -23,8 +29,77 @@ def draft(draft_id="phone-capture", *, title="Broken checkout", evidence=None):
     }
 
 
+def test_unfiled_drafts_encrypt_private_content_and_authenticate_the_account(tmp_path):
+    path = tmp_path / "unfiled.sqlite3"
+    store = UnfiledDraftStore(path, encryption_key=ENCRYPTION_KEY)
+
+    created = store.replace("timmy", 0, [draft()])
+
+    with sqlite3.connect(path) as connection:
+        payload = connection.execute(
+            "SELECT drafts FROM unfiled_drafts WHERE login = 'timmy'"
+        ).fetchone()[0]
+        connection.execute(
+            "INSERT INTO unfiled_drafts(login, revision, drafts) VALUES (?, ?, ?)",
+            ("alexander", 1, payload),
+        )
+    assert payload.startswith("v1:")
+    assert "Broken checkout" not in payload
+    assert "Steps from the field" not in payload
+    assert "cG5nLWJ5dGVz" not in payload
+    assert store.get("timmy") == created
+    with pytest.raises(
+        unfiled_draft_store.UnfiledDraftEncryptionError,
+        match="could not be decrypted",
+    ):
+        store.get("alexander")
+
+
+def test_unfiled_drafts_migrate_plaintext_without_changing_revision_or_order(tmp_path):
+    path = tmp_path / "unfiled.sqlite3"
+    store = UnfiledDraftStore(path, encryption_key=ENCRYPTION_KEY)
+    legacy = [draft(), draft("second", title="Second")]
+    with sqlite3.connect(path) as connection:
+        connection.execute(
+            "INSERT INTO unfiled_drafts(login, revision, drafts) VALUES (?, ?, ?)",
+            ("timmy", 7, json.dumps(legacy, separators=(",", ":"))),
+        )
+
+    assert store.get("timmy") == {"revision": 7, "drafts": legacy}
+    with sqlite3.connect(path) as connection:
+        migrated = connection.execute(
+            "SELECT revision, drafts FROM unfiled_drafts WHERE login = 'timmy'"
+        ).fetchone()
+    assert migrated[0] == 7
+    assert migrated[1].startswith("v1:")
+    assert "Broken checkout" not in migrated[1]
+
+
+def test_unfiled_drafts_reject_tampered_ciphertext(tmp_path):
+    path = tmp_path / "unfiled.sqlite3"
+    store = UnfiledDraftStore(path, encryption_key=ENCRYPTION_KEY)
+    store.replace("timmy", 0, [draft()])
+    with sqlite3.connect(path) as connection:
+        payload = connection.execute(
+            "SELECT drafts FROM unfiled_drafts WHERE login = 'timmy'"
+        ).fetchone()[0]
+        replacement = "A" if payload[-1] != "A" else "B"
+        connection.execute(
+            "UPDATE unfiled_drafts SET drafts = ? WHERE login = 'timmy'",
+            (payload[:-1] + replacement,),
+        )
+
+    with pytest.raises(
+        unfiled_draft_store.UnfiledDraftEncryptionError,
+        match="could not be decrypted",
+    ):
+        store.get("timmy")
+
+
 def test_unfiled_drafts_are_revisioned_ordered_and_account_scoped(tmp_path):
-    store = UnfiledDraftStore(tmp_path / "unfiled.sqlite3")
+    store = UnfiledDraftStore(
+        tmp_path / "unfiled.sqlite3", encryption_key=ENCRYPTION_KEY
+    )
 
     created = store.replace(" Timmy ", 0, [draft(), draft("second", title="Second")])
 
@@ -37,7 +112,12 @@ def test_unfiled_drafts_are_revisioned_ordered_and_account_scoped(tmp_path):
 
 
 def test_unfiled_drafts_bound_collection_and_decoded_evidence(tmp_path):
-    store = UnfiledDraftStore(tmp_path / "unfiled.sqlite3", limit=2, max_total_bytes=12)
+    store = UnfiledDraftStore(
+        tmp_path / "unfiled.sqlite3",
+        encryption_key=ENCRYPTION_KEY,
+        limit=2,
+        max_total_bytes=12,
+    )
 
     with pytest.raises(ValueError, match="limited to 2"):
         store.replace("timmy", 0, [draft("one", evidence=[]), draft("two", evidence=[]), draft("three", evidence=[])])
@@ -52,7 +132,9 @@ def test_unfiled_drafts_bound_collection_and_decoded_evidence(tmp_path):
 
 
 def test_unfiled_drafts_allow_untitled_photo_evidence_but_reject_empty_records(tmp_path):
-    store = UnfiledDraftStore(tmp_path / "unfiled.sqlite3")
+    store = UnfiledDraftStore(
+        tmp_path / "unfiled.sqlite3", encryption_key=ENCRYPTION_KEY
+    )
     photo_only = draft(title="")
 
     validated = main.UnfiledDraft.model_validate(photo_only).model_dump()
@@ -66,7 +148,9 @@ def test_unfiled_drafts_allow_untitled_photo_evidence_but_reject_empty_records(t
 
 
 def test_unfiled_drafts_validate_and_round_trip_complete_filing_plan(tmp_path):
-    store = UnfiledDraftStore(tmp_path / "unfiled.sqlite3")
+    store = UnfiledDraftStore(
+        tmp_path / "unfiled.sqlite3", encryption_key=ENCRYPTION_KEY
+    )
     planned = draft(evidence=[])
     planned.pop("evidence")
     planned["filing_plan"] = {
@@ -102,6 +186,10 @@ async def test_unfiled_draft_api_is_account_scoped_csrf_protected_and_conflict_s
     monkeypatch.setenv("STACKCHAIN_SESSION_DB", str(tmp_path / "sessions.sqlite3"))
     monkeypatch.setenv("STACKCHAIN_LOGIN_ATTEMPT_DB", str(tmp_path / "login.sqlite3"))
     monkeypatch.setenv("STACKCHAIN_UNFILED_DRAFT_DB", str(tmp_path / "drafts.sqlite3"))
+    monkeypatch.setenv(
+        "STACKCHAIN_UNFILED_DRAFT_ENCRYPTION_KEY",
+        "ZGRkZGRkZGRkZGRkZGRkZGRkZGRkZGRkZGRkZGRkZGQ=",
+    )
     identity = {"login": "Timmy"}
 
     async def user():
@@ -133,6 +221,10 @@ async def test_unfiled_draft_api_is_account_scoped_csrf_protected_and_conflict_s
         fetched = await client.get("/api/v1/unfiled-drafts")
         identity["login"] = "Alexander"
         isolated = await client.get("/api/v1/unfiled-drafts")
+        monkeypatch.delenv("STACKCHAIN_UNFILED_DRAFT_ENCRYPTION_KEY")
+        unavailable = await client.get("/api/v1/unfiled-drafts")
+        monkeypatch.setenv("STACKCHAIN_UNFILED_DRAFT_ENCRYPTION_KEY", "not-base64")
+        malformed = await client.get("/api/v1/unfiled-drafts")
 
     assert forbidden.status_code == 403
     assert saved.status_code == 200
@@ -144,3 +236,7 @@ async def test_unfiled_draft_api_is_account_scoped_csrf_protected_and_conflict_s
     assert fetched.json() == saved.json()
     assert fetched.headers["cache-control"] == "no-store"
     assert isolated.json() == {"revision": 0, "drafts": []}
+    assert unavailable.status_code == 503
+    assert unavailable.json()["detail"] == "Draft synchronization is unavailable"
+    assert malformed.status_code == 503
+    assert malformed.json()["detail"] == "Draft synchronization is unavailable"