Fix pytest for SecureTar v3

Patch crypto_secretstream_xchacha20poly1305_init_push() to generate
a deterministic header for testing. This allows us to use a fixed
fixture for SecureTar v3 encrypted backups.

homeassistant/components/backup/const.py

@@ -34,4 +34,4 @@ EXCLUDE_DATABASE_FROM_BACKUP = [
     "home-assistant_v2.db-wal",
 ]
 
-SECURETAR_CREATE_VERSION = 2
+SECURETAR_CREATE_VERSION = 3

tests/components/backup/test_manager.py

@@ -3542,7 +3542,7 @@ async def test_initiate_backup_per_agent_encryption(
         await hass.async_block_till_done()
 
     assert mock_secure_tar_archive.mock_calls[0] == call(
-        ANY, ANY, "w", bufsize=4194304, create_version=2, password=inner_tar_password
+        ANY, ANY, "w", bufsize=4194304, create_version=3, password=inner_tar_password
     )
 
     result = await ws_client.receive_json()

tests/components/backup/test_util.py

@@ -5,10 +5,13 @@ from __future__ import annotations
 import asyncio
 from collections.abc import AsyncIterator
 import dataclasses
+import hashlib
+import os
 from pathlib import Path
 import tarfile
 from unittest.mock import Mock, patch
 
+import nacl.bindings.crypto_secretstream as nss
 import pytest
 import securetar
 
@@ -25,6 +28,32 @@ from homeassistant.core import HomeAssistant
 from tests.common import get_fixture_path
 
 
+def _deterministic_init_push(
+    state: nss.crypto_secretstream_xchacha20poly1305_state, key: bytes
+) -> bytes:
+    """Replace init_push with init_pull + deterministic header from os.urandom.
+
+    libsodium's init_push generates random bytes internally, bypassing os.urandom.
+    This replacement generates the header via os.urandom (which can be patched for
+    deterministic tests) and uses init_pull to correctly initialize the state.
+    """
+    header = os.urandom(nss.crypto_secretstream_xchacha20poly1305_HEADERBYTES)
+    nss.crypto_secretstream_xchacha20poly1305_init_pull(state, header, key)
+    return header
+
+
+def _make_deterministic_urandom() -> callable:
+    """Create a deterministic os.urandom replacement."""
+    call_idx = 0
+
+    def deterministic_urandom(n: int) -> bytes:
+        nonlocal call_idx
+        call_idx += 1
+        return hashlib.sha256(f"deterministic-{call_idx}".encode()).digest()[:n]
+
+    return deterministic_urandom
+
+
 @pytest.mark.parametrize(
     ("backup_json_content", "expected_backup"),
     [
@@ -432,14 +461,14 @@ async def test_decrypted_backup_streamer_wrong_password(hass: HomeAssistant) ->
                 AddonInfo(name="Core 2", slug="core2", version="1.0.0"),
             ],
             40960,  # 4 x 10240 byte of padding
-            "test_backups/c0cb53bd.tar",
+            "test_backups/c0cb53bd.tar.encrypted_v3",
         ),
         (
             [
                 AddonInfo(name="Core 1", slug="core1", version="1.0.0"),
             ],
             30720,  # 3 x 10240 byte of padding
-            "test_backups/c0cb53bd.tar.encrypted_skip_core2",
+            "test_backups/c0cb53bd.tar.encrypted_v3_skip_core2",
         ),
     ],
 )
@@ -477,16 +506,17 @@ async def test_encrypted_backup_streamer(
     async def open_backup() -> AsyncIterator[bytes]:
         return send_backup()
 
-    # Patch os.urandom to return values matching the nonce used in the encrypted
-    # test backup. The backup has three inner tar files, but we need an extra nonce
-    # for a future planned supervisor.tar.
-    with patch("os.urandom") as mock_randbytes:
-        mock_randbytes.side_effect = (
-            bytes.fromhex("bd34ea6fc93b0614ce7af2b44b4f3957"),
-            bytes.fromhex("1296d6f7554e2cb629a3dc4082bae36c"),
-            bytes.fromhex("8b7a58e48faf2efb23845eb3164382e0"),
-            bytes.fromhex("00000000000000000000000000000000"),
-        )
+    # Patch os.urandom for deterministic key derivation salts, and patch
+    # crypto_secretstream init_push to use os.urandom for the stream header
+    # instead of libsodium's internal CSPRNG.
+    with (
+        patch("os.urandom", side_effect=_make_deterministic_urandom()),
+        patch(
+            "nacl.bindings.crypto_secretstream"
+            ".crypto_secretstream_xchacha20poly1305_init_push",
+            side_effect=_deterministic_init_push,
+        ),
+    ):
         encryptor = EncryptedBackupStreamer(hass, backup, open_backup, "hunter2")
 
         assert encryptor.backup() == dataclasses.replace(
@@ -587,7 +617,9 @@ async def test_encrypted_backup_streamer_random_nonce(hass: HomeAssistant) -> No
     decrypted_backup_path = get_fixture_path(
         "test_backups/c0cb53bd.tar.decrypted", DOMAIN
     )
-    encrypted_backup_path = get_fixture_path("test_backups/c0cb53bd.tar", DOMAIN)
+    encrypted_backup_path = get_fixture_path(
+        "test_backups/c0cb53bd.tar.encrypted_v3", DOMAIN
+    )
     backup = AgentBackup(
         addons=[
             AddonInfo(name="Core 1", slug="core1", version="1.0.0"),