legacy: move pbkdf2 static method from FlexiKey to Pbkdf2FileMixin

src/borg/crypto/key.py

@@ -2,7 +2,7 @@
 import hmac
 import os
 import textwrap
-from hashlib import sha256, pbkdf2_hmac
+from hashlib import sha256
 from pathlib import Path
 from typing import Literal, ClassVar
 from collections.abc import Callable
@@ -443,12 +443,6 @@ def decrypt_key_file(self, data, passphrase):
             else:
                 raise UnsupportedKeyFormatError()
 
-    @staticmethod
-    def pbkdf2(passphrase, salt, iterations, output_len_in_bytes):
-        if os.environ.get("BORG_TESTONLY_WEAKEN_KDF") == "1":
-            iterations = 1
-        return pbkdf2_hmac("sha256", passphrase.encode("utf-8"), salt, iterations, output_len_in_bytes)
-
     @staticmethod
     def argon2(
         passphrase: str,

src/borg/legacy/crypto/key.py

@@ -1,5 +1,6 @@
 import hmac
 import os
+from hashlib import pbkdf2_hmac
 
 from ...constants import *  # NOQA
 from ...crypto.low_level import AES256_CTR_HMAC_SHA256, AES256_CTR_BLAKE2b, hmac_sha256
@@ -12,6 +13,12 @@
 class Pbkdf2FileMixin:
     """Mixin for borg 1.x key files encrypted with PBKDF2 + AES-CTR."""
 
+    @staticmethod
+    def pbkdf2(passphrase, salt, iterations, output_len_in_bytes):
+        if os.environ.get("BORG_TESTONLY_WEAKEN_KDF") == "1":
+            iterations = 1
+        return pbkdf2_hmac("sha256", passphrase.encode("utf-8"), salt, iterations, output_len_in_bytes)
+
     def decrypt_key_file(self, data, passphrase):
         unpacker = get_limited_unpacker("key")
         unpacker.feed(data)

src/borg/testsuite/crypto/crypto_test.py

@@ -9,7 +9,7 @@
 from ...crypto.low_level import hmac_sha256
 from ...legacy.crypto.low_level import AES
 from hashlib import sha256
-from ...crypto.key import CHPOKeyfileKey, AESOCBRepoKey, FlexiKey, KeyBase, PlaintextKey
+from ...crypto.key import CHPOKeyfileKey, AESOCBRepoKey, KeyBase, PlaintextKey
 from ...legacy.crypto.key import KeyfileKey as LegacyKeyfileKey
 from ...helpers import msgpack, bin_to_hex
 
@@ -228,7 +228,7 @@ def test_decrypt_key_file_pbkdf2_sha256_aes256_ctr_hmac_sha256():
     plain = b"hello"
     salt = b"salt" * 4
     passphrase = "hello, pass phrase"
-    key = FlexiKey.pbkdf2(passphrase, salt, 1, 32)
+    key = LegacyKeyfileKey.pbkdf2(passphrase, salt, 1, 32)
     hash = hmac_sha256(key, plain)
     data = AES(key, b"\0" * 16).encrypt(plain)
     encrypted = msgpack.packb(