Agent: Add InPlaceEncryptor

InPlaceEncryptor encrypts a file in place. It accepts a callable that
performs the actual bit manipulation. This allows the in-place
encryption functionality to be easily reused, while the actual
encryption algorithm can be changed.

monkey/infection_monkey/ransomware/in_place_encryptor.py

@@ -0,0 +1,21 @@
+from pathlib import Path
+from typing import Callable
+
+
+class InPlaceEncryptor:
+    def __init__(self, encrypt_bytes: Callable[[bytes], bytes], chunk_size: int = 64):
+        self._encrypt_bytes = encrypt_bytes
+        self._chunk_size = chunk_size
+
+    def __call__(self, filepath: Path):
+        with open(filepath, "rb+") as f:
+            data = f.read(self._chunk_size)
+            while data:
+                num_bytes_read = len(data)
+
+                encrypted_data = self._encrypt_bytes(data)
+
+                f.seek(-num_bytes_read, 1)
+                f.write(encrypted_data)
+
+                data = f.read(self._chunk_size)

monkey/tests/unit_tests/infection_monkey/ransomware/test_in_place_encryptor.py

@@ -0,0 +1,49 @@
+import os
+
+import pytest
+from tests.unit_tests.infection_monkey.ransomware.ransomware_target_files import (
+    ALL_ZEROS_PDF,
+    ALL_ZEROS_PDF_CLEARTEXT_SHA256,
+    ALL_ZEROS_PDF_ENCRYPTED_SHA256,
+    TEST_KEYBOARD_TXT,
+    TEST_KEYBOARD_TXT_CLEARTEXT_SHA256,
+    TEST_KEYBOARD_TXT_ENCRYPTED_SHA256,
+)
+from tests.utils import hash_file
+
+from infection_monkey.ransomware.in_place_encryptor import InPlaceEncryptor
+from infection_monkey.utils.bit_manipulators import flip_bits
+
+
+@pytest.fixture(scope="module")
+def in_place_bitflip_encryptor():
+    return InPlaceEncryptor(flip_bits, 64)
+
+
+@pytest.mark.parametrize(
+    "file_name,cleartext_hash,encrypted_hash",
+    [
+        (TEST_KEYBOARD_TXT, TEST_KEYBOARD_TXT_CLEARTEXT_SHA256, TEST_KEYBOARD_TXT_ENCRYPTED_SHA256),
+        (ALL_ZEROS_PDF, ALL_ZEROS_PDF_CLEARTEXT_SHA256, ALL_ZEROS_PDF_ENCRYPTED_SHA256),
+    ],
+)
+def test_file_encrypted(
+    in_place_bitflip_encryptor, ransomware_target, file_name, cleartext_hash, encrypted_hash
+):
+    test_keyboard = ransomware_target / file_name
+
+    assert hash_file(test_keyboard) == cleartext_hash
+
+    in_place_bitflip_encryptor(test_keyboard)
+
+    assert hash_file(test_keyboard) == encrypted_hash
+
+
+def test_file_encrypted_in_place(in_place_bitflip_encryptor, ransomware_target):
+    test_keyboard = ransomware_target / TEST_KEYBOARD_TXT
+
+    expected_inode = os.stat(test_keyboard).st_ino
+    in_place_bitflip_encryptor(test_keyboard)
+    actual_inode = os.stat(test_keyboard).st_ino
+
+    assert expected_inode == actual_inode