TST: increase code coverage

pypdf/_crypt_providers/_cryptography.py

@@ -62,21 +62,21 @@ def encrypt(self, data: bytes) -> bytes:
         return iv + encryptor.update(data) + encryptor.finalize()
 
     def decrypt(self, data: bytes) -> bytes:
-        if len(data) == 0:
-            return data
         iv = data[:16]
         data = data[16:]
-        if len(data) % 16:
+        # for empty encrypted data
+        if not data:
+            return data
+
+        # just for robustness, it does not happen under normal circumstances
+        if len(data) % 16 != 0:
             pad = padding.PKCS7(128).padder()
             data = pad.update(data) + pad.finalize()
 
         cipher = Cipher(self.alg, CBC(iv))
         decryptor = cipher.decryptor()
         d = decryptor.update(data) + decryptor.finalize()
-        if len(d) == 0:
-            return d
-        else:
-            return d[: -d[-1]]
+        return d[: -d[-1]]
 
 
 def rc4_encrypt(key: bytes, data: bytes) -> bytes:

pypdf/_crypt_providers/_pycryptodome.py

@@ -55,18 +55,19 @@ def encrypt(self, data: bytes) -> bytes:
         return iv + aes.encrypt(data)
 
     def decrypt(self, data: bytes) -> bytes:
-        if len(data) == 0:
-            return data
         iv = data[:16]
         data = data[16:]
-        if len(data) % 16:
+        # for empty encrypted data
+        if not data:
+            return data
+
+        # just for robustness, it does not happen under normal circumstances
+        if len(data) % 16 != 0:
             data = pad(data, 16)
+
         aes = AES.new(self.key, AES.MODE_CBC, iv)
         d = aes.decrypt(data)
-        if len(d) == 0:
-            return d
-        else:
-            return d[: -d[-1]]
+        return d[: -d[-1]]
 
 
 def rc4_encrypt(key: bytes, data: bytes) -> bytes:

tests/test_encryption.py

@@ -1,12 +1,12 @@
-"""Test the pypdf.encryption module."""
+"""Test the pypdf._encryption module."""
 import secrets
 from pathlib import Path
 
 import pytest
 
 import pypdf
 from pypdf import PasswordType, PdfReader, PdfWriter
-from pypdf._encryption import AlgV5, CryptRC4
+from pypdf._encryption import AlgV5, CryptAES, CryptRC4
 from pypdf.errors import DependencyError, PdfReadError
 
 try:
@@ -344,3 +344,11 @@ def test_pdf_encrypt_multiple(pdf_file_path, count):
     page = reader.pages[0]
     text1 = page.extract_text()
     assert text0 == text1
+
+
+@pytest.mark.skipif(not HAS_PYCRYPTODOME and not HAS_CRYPTOGRAPHY, reason="No pycryptodome / cryptography")
+def test_aes_decrypt_corrupted_data():
+    """Just for robustness"""
+    aes = CryptAES(secrets.token_bytes(16))
+    for num in [0, 17, 32]:
+        aes.decrypt(secrets.token_bytes(num))