feat(v2): complete v2 reimplementation

tests/security/test_crypto_leakage.py

@@ -0,0 +1,21 @@
+from __future__ import annotations
+
+import os
+
+import pytest
+from backup_tool.security.repository_crypto import (
+    RepositoryKeyError,
+    decrypt_object,
+    encrypt_object,
+    object_aad,
+)
+
+
+def test_encrypted_object_hides_plaintext_and_rejects_tampering() -> None:
+    key = os.urandom(32)
+    aad = object_aad("repository", "epoch", "blob", "identity")
+    stored = encrypt_object(key, aad, b"secret-content")
+    assert b"secret-content" not in stored
+    assert decrypt_object(key, aad, stored) == b"secret-content"
+    with pytest.raises(RepositoryKeyError):
+        decrypt_object(key, aad, stored[:-1] + bytes([stored[-1] ^ 1]))