always implicitly require manifest TAMs

remove a lot of complexity from the code that was just there to
support legacy borg versions < 1.0.9 which did not TAM authenticate
the manifest.

since then, borg writes TAM authentication to the manifest,
even if the repo is unencrypted.
if the repo is unencrypted, it did not check the somehow pointless
authentication that was generated without any secret, but
if we add that fake TAM, we can also verify the fake TAM.

if somebody explicitly switches off all crypto, they can not
expect authentication.

for everybody else, borg now always generates the TAM and also
verifies it.

6 files changed, 15 insertions, 91 deletions

diff --git a/src/borg/archiver/key_cmds.py b/src/borg/archiver/key_cmds.py
index a365848ff..bdc93a556 100644
--- a/src/borg/archiver/key_cmds.py
+++ b/src/borg/archiver/key_cmds.py
@@ -63,7 +63,7 @@ class KeysMixIn:
                 print("Change not needed or not supported.")
                 return EXIT_WARNING
 
-        for name in ("repository_id", "crypt_key", "id_key", "chunk_seed", "tam_required", "sessionid", "cipher"):
+        for name in ("repository_id", "crypt_key", "id_key", "chunk_seed", "sessionid", "cipher"):
             value = getattr(key, name)
             setattr(key_new, name, value)
 
diff --git a/src/borg/archiver/rcreate_cmd.py b/src/borg/archiver/rcreate_cmd.py
index 8fce7dbbe..e6545a03a 100644
--- a/src/borg/archiver/rcreate_cmd.py
+++ b/src/borg/archiver/rcreate_cmd.py
@@ -3,7 +3,7 @@ import argparse
 from ._common import with_repository, with_other_repository, Highlander
 from ..cache import Cache
 from ..constants import *  # NOQA
-from ..crypto.key import key_creator, key_argument_names, tam_required_file
+from ..crypto.key import key_creator, key_argument_names
 from ..helpers import EXIT_WARNING
 from ..helpers import location_validator, Location
 from ..helpers import parse_storage_quota
@@ -35,10 +35,6 @@ class RCreateMixIn:
         repository.commit(compact=False)
         with Cache(repository, manifest, warn_if_unencrypted=False):
             pass
-        if key.tam_required:
-            tam_file = tam_required_file(repository)
-            open(tam_file, "w").close()
-
         if key.NAME != "plaintext":
             logger.warning(
                 "\n"
diff --git a/src/borg/crypto/key.py b/src/borg/crypto/key.py
index 3fb4818aa..d6d6b32e5 100644
--- a/src/borg/crypto/key.py
+++ b/src/borg/crypto/key.py
@@ -136,16 +136,6 @@ def key_factory(repository, manifest_chunk, *, ro_cls=RepoObj):
     return identify_key(manifest_data).detect(repository, manifest_data)
 
 
-def tam_required_file(repository):
-    security_dir = get_security_dir(bin_to_hex(repository.id), legacy=(repository.version == 1))
-    return os.path.join(security_dir, "tam_required")
-
-
-def tam_required(repository):
-    file = tam_required_file(repository)
-    return os.path.isfile(file)
-
-
 def uses_same_chunker_secret(other_key, key):
     """is the chunker secret the same?"""
     # avoid breaking the deduplication by a different chunker secret
@@ -211,7 +201,6 @@ class KeyBase:
         self.TYPE_STR = bytes([self.TYPE])
         self.repository = repository
         self.target = None  # key location file path / repo obj
-        self.tam_required = True
         self.copy_crypt_key = False
 
     def id_hash(self, data):
@@ -253,39 +242,25 @@ class KeyBase:
         tam["hmac"] = hmac.digest(tam_key, packed, "sha512")
         return msgpack.packb(metadata_dict)
 
-    def unpack_and_verify_manifest(self, data, force_tam_not_required=False):
-        """Unpack msgpacked *data* and return (object, did_verify)."""
+    def unpack_and_verify_manifest(self, data):
+        """Unpack msgpacked *data* and return manifest."""
         if data.startswith(b"\xc1" * 4):
             # This is a manifest from the future, we can't read it.
             raise UnsupportedManifestError()
-        tam_required = self.tam_required
-        if force_tam_not_required and tam_required:
-            logger.warning("Manifest authentication DISABLED.")
-            tam_required = False
         data = bytearray(data)
         unpacker = get_limited_unpacker("manifest")
         unpacker.feed(data)
         unpacked = unpacker.unpack()
         if AUTHENTICATED_NO_KEY:
-            return unpacked, True  # True is a lie.
+            return unpacked
         if "tam" not in unpacked:
-            if tam_required:
-                raise TAMRequiredError(self.repository._location.canonical_path())
-            else:
-                logger.debug("Manifest TAM not found and not required")
-                return unpacked, False
+            raise TAMRequiredError(self.repository._location.canonical_path())
         tam = unpacked.pop("tam", None)
         if not isinstance(tam, dict):
             raise TAMInvalid()
         tam_type = tam.get("type", "<none>")
         if tam_type != "HKDF_HMAC_SHA512":
-            if tam_required:
-                raise TAMUnsupportedSuiteError(repr(tam_type))
-            else:
-                logger.debug(
-                    "Ignoring manifest TAM made with unsupported suite, since TAM is not required: %r", tam_type
-                )
-                return unpacked, False
+            raise TAMUnsupportedSuiteError(repr(tam_type))
         tam_hmac = tam.get("hmac")
         tam_salt = tam.get("salt")
         if not isinstance(tam_salt, (bytes, str)) or not isinstance(tam_hmac, (bytes, str)):
@@ -299,7 +274,7 @@ class KeyBase:
         if not hmac.compare_digest(calculated_hmac, tam_hmac):
             raise TAMInvalid()
         logger.debug("TAM-verified manifest")
-        return unpacked, True
+        return unpacked
 
     def unpack_and_verify_archive(self, data, force_tam_not_required=False):
         """Unpack msgpacked *data* and return (object, did_verify)."""
@@ -357,10 +332,6 @@ class PlaintextKey(KeyBase):
     chunk_seed = 0
     logically_encrypted = False
 
-    def __init__(self, repository):
-        super().__init__(repository)
-        self.tam_required = False
-
     @classmethod
     def create(cls, repository, args, **kw):
         logger.info('Encryption NOT enabled.\nUse the "--encryption=repokey|keyfile" to enable encryption.')
@@ -526,7 +497,6 @@ class FlexiKey:
             self.crypt_key = key.crypt_key
             self.id_key = key.id_key
             self.chunk_seed = key.chunk_seed
-            self.tam_required = key.get("tam_required", tam_required(self.repository))
             return True
         return False
 
@@ -639,7 +609,6 @@ class FlexiKey:
             crypt_key=self.crypt_key,
             id_key=self.id_key,
             chunk_seed=self.chunk_seed,
-            tam_required=self.tam_required,
         )
         data = self.encrypt_key_file(msgpack.packb(key.as_dict()), passphrase, algorithm)
         key_data = "\n".join(textwrap.wrap(b2a_base64(data).decode("ascii")))
diff --git a/src/borg/item.pyx b/src/borg/item.pyx
index 5da91c2ed..04dd884f2 100644
--- a/src/borg/item.pyx
+++ b/src/borg/item.pyx
@@ -467,7 +467,7 @@ cdef class Key(PropDict):
     crypt_key = PropDictProperty(bytes)
     id_key = PropDictProperty(bytes)
     chunk_seed = PropDictProperty(int)
-    tam_required = PropDictProperty(bool)
+    tam_required = PropDictProperty(bool)  # legacy. borg now implicitly always requires TAM.
 
     def update_internal(self, d):
         # legacy support for migration (data from old msgpacks comes in as bytes always, but sometimes we want str)
@@ -650,7 +650,6 @@ class ItemDiff:
         self._can_compare_chunk_ids = can_compare_chunk_ids
         self._chunk_1 = chunk_1
         self._chunk_2 = chunk_2
-
         self._changes = {}
 
         if self._item1.is_link() or self._item2.is_link():
diff --git a/src/borg/manifest.py b/src/borg/manifest.py
index 592b53194..0768ce44c 100644
--- a/src/borg/manifest.py
+++ b/src/borg/manifest.py
@@ -1,6 +1,4 @@
 import enum
-import os
-import os.path
 import re
 from collections import abc, namedtuple
 from datetime import datetime, timedelta, timezone
@@ -229,7 +227,6 @@ class Manifest:
         self.repo_objs = ro_cls(key)
         self.repository = repository
         self.item_keys = frozenset(item_keys) if item_keys is not None else ITEM_KEYS
-        self.tam_verified = False
         self.timestamp = None
 
     @property
@@ -241,9 +238,9 @@ class Manifest:
         return parse_timestamp(self.timestamp)
 
     @classmethod
-    def load(cls, repository, operations, key=None, force_tam_not_required=False, *, ro_cls=RepoObj):
+    def load(cls, repository, operations, key=None, *, ro_cls=RepoObj):
         from .item import ManifestItem
-        from .crypto.key import key_factory, tam_required_file, tam_required
+        from .crypto.key import key_factory
         from .repository import Repository
 
         try:
@@ -254,9 +251,7 @@ class Manifest:
             key = key_factory(repository, cdata, ro_cls=ro_cls)
         manifest = cls(key, repository, ro_cls=ro_cls)
         _, data = manifest.repo_objs.parse(cls.MANIFEST_ID, cdata)
-        manifest_dict, manifest.tam_verified = key.unpack_and_verify_manifest(
-            data, force_tam_not_required=force_tam_not_required
-        )
+        manifest_dict = key.unpack_and_verify_manifest(data)
         m = ManifestItem(internal_dict=manifest_dict)
         manifest.id = manifest.repo_objs.id_hash(data)
         if m.get("version") not in (1, 2):
@@ -268,17 +263,6 @@ class Manifest:
         manifest.item_keys = ITEM_KEYS
         manifest.item_keys |= frozenset(m.config.get("item_keys", []))  # new location of item_keys since borg2
         manifest.item_keys |= frozenset(m.get("item_keys", []))  # legacy: borg 1.x: item_keys not in config yet
-
-        if manifest.tam_verified:
-            manifest_required = manifest.config.get("tam_required", False)
-            security_required = tam_required(repository)
-            if manifest_required and not security_required:
-                logger.debug("Manifest is TAM verified and says TAM is required, updating security database...")
-                file = tam_required_file(repository)
-                open(file, "w").close()
-            if not manifest_required and security_required:
-                logger.debug("Manifest is TAM verified and says TAM is *not* required, updating security database...")
-                os.unlink(tam_required_file(repository))
         manifest.check_repository_compatibility(operations)
         return manifest
 
@@ -310,8 +294,6 @@ class Manifest:
     def write(self):
         from .item import ManifestItem
 
-        if self.key.tam_required:
-            self.config["tam_required"] = True
         # self.timestamp needs to be strictly monotonically increasing. Clocks often are not set correctly
         if self.timestamp is None:
             self.timestamp = datetime.now(tz=timezone.utc).isoformat(timespec="microseconds")
@@ -331,7 +313,6 @@ class Manifest:
             timestamp=self.timestamp,
             config=StableDict(self.config),
         )
-        self.tam_verified = True
         data = self.key.pack_and_authenticate_metadata(manifest.as_dict())
         self.id = self.repo_objs.id_hash(data)
         self.repository.put(self.MANIFEST_ID, self.repo_objs.format(self.MANIFEST_ID, {}, data))
diff --git a/src/borg/testsuite/key.py b/src/borg/testsuite/key.py
index 73d9df35d..a8fd37681 100644
--- a/src/borg/testsuite/key.py
+++ b/src/borg/testsuite/key.py
@@ -272,40 +272,20 @@ class TestTAM:
         with pytest.raises(msgpack.UnpackException):
             key.unpack_and_verify_manifest(blob)
 
-    def test_missing_when_required(self, key):
+    def test_missing(self, key):
         blob = msgpack.packb({})
         with pytest.raises(TAMRequiredError):
             key.unpack_and_verify_manifest(blob)
         with pytest.raises(TAMRequiredError):
             key.unpack_and_verify_archive(blob)
 
-    def test_missing(self, key):
-        blob = msgpack.packb({})
-        key.tam_required = False
-        unpacked, verified = key.unpack_and_verify_manifest(blob)
-        assert unpacked == {}
-        assert not verified
-        unpacked, verified, _ = key.unpack_and_verify_archive(blob)
-        assert unpacked == {}
-        assert not verified
-
-    def test_unknown_type_when_required(self, key):
+    def test_unknown_type(self, key):
         blob = msgpack.packb({"tam": {"type": "HMAC_VOLLBIT"}})
         with pytest.raises(TAMUnsupportedSuiteError):
             key.unpack_and_verify_manifest(blob)
         with pytest.raises(TAMUnsupportedSuiteError):
             key.unpack_and_verify_archive(blob)
 
-    def test_unknown_type(self, key):
-        blob = msgpack.packb({"tam": {"type": "HMAC_VOLLBIT"}})
-        key.tam_required = False
-        unpacked, verified = key.unpack_and_verify_manifest(blob)
-        assert unpacked == {}
-        assert not verified
-        unpacked, verified, _ = key.unpack_and_verify_archive(blob)
-        assert unpacked == {}
-        assert not verified
-
     @pytest.mark.parametrize(
         "tam, exc",
         (
@@ -360,8 +340,7 @@ class TestTAM:
         unpacked = msgpack.unpackb(blob)
         assert unpacked["tam"]["type"] == "HKDF_HMAC_SHA512"
 
-        unpacked, verified = key.unpack_and_verify_manifest(blob)
-        assert verified
+        unpacked = key.unpack_and_verify_manifest(blob)
         assert unpacked["foo"] == "bar"
         assert "tam" not in unpacked