[feature] Default-AES-Implementierung kann optional installiert werden.

Eine auf cryptography basierende AES-Implementierung kann optional (`bec2format[aes]`) installiert werden.

bec2format/__init__.py

@@ -36,3 +36,8 @@
     FormatError,
     UnsupportedLegacyFirmwareError,
 )
+
+try:
+    from .extras import aes
+except ImportError:
+    pass

bec2format/extras/aes.py

@@ -0,0 +1,26 @@
+from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+
+from bec2format import AES128, register_AES128
+
+
+@register_AES128
+class AES128Proxy(AES128):
+    def __init__(self, key: bytes, iv: bytes) -> None:
+        super().__init__(key, iv)
+        self._cipher = Cipher(
+            algorithms.AES128(self._key), modes.CBC(self._iv or b"\x00" * 16)
+        )
+
+    def encrypt(self, data: bytes) -> bytes:
+        pad_length = -len(data) % AES128.BLOCK_SIZE
+        pad = b"" if pad_length == 0 else bytes([0x00] * pad_length)
+        encryptor = self._cipher.encryptor()
+        return encryptor.update(data + pad) + encryptor.finalize()
+
+    def decrypt(self, data: bytes) -> bytes:
+        decryptor = self._cipher.decryptor()
+        plaintext_padded = decryptor.update(data) + decryptor.finalize()
+        return plaintext_padded.rstrip(b"\0")
+
+    def mac(self, data: bytes) -> bytes:
+        return self.encrypt(data)[-16:]

pyproject.toml

@@ -7,6 +7,11 @@ license = "MIT"
 
 [tool.poetry.dependencies]
 python = ">=3.10,<3.11"
+cryptography = { version = "*", optional = true }
+
+[tool.poetry.extras]
+aes = ["cryptography"]
+
 
 [tool.poetry.dev-dependencies]
 pytest = "*"