[aes] Add multiple padding modes in CBC

Authored by: elyse0

test/test_aes.py

@@ -24,6 +24,8 @@ from yt_dlp.aes import (
     aes_encrypt,
     aes_gcm_decrypt_and_verify,
     aes_gcm_decrypt_and_verify_bytes,
+    key_expansion,
+    pad_block,
 )
 from yt_dlp.dependencies import Cryptodome_AES
 from yt_dlp.utils import bytes_to_intlist, intlist_to_bytes
@@ -112,6 +114,41 @@ class TestAES(unittest.TestCase):
         decrypted = intlist_to_bytes(aes_ecb_decrypt(data, self.key, self.iv))
         self.assertEqual(decrypted.rstrip(b'\x08'), self.secret_msg)
 
+    def test_key_expansion(self):
+        key = '4f6bdaa39e2f8cb07f5e722d9edef314'
+
+        self.assertEqual(key_expansion(bytes_to_intlist(bytearray.fromhex(key))), [
+            0x4F, 0x6B, 0xDA, 0xA3, 0x9E, 0x2F, 0x8C, 0xB0, 0x7F, 0x5E, 0x72, 0x2D, 0x9E, 0xDE, 0xF3, 0x14,
+            0x53, 0x66, 0x20, 0xA8, 0xCD, 0x49, 0xAC, 0x18, 0xB2, 0x17, 0xDE, 0x35, 0x2C, 0xC9, 0x2D, 0x21,
+            0x8C, 0xBE, 0xDD, 0xD9, 0x41, 0xF7, 0x71, 0xC1, 0xF3, 0xE0, 0xAF, 0xF4, 0xDF, 0x29, 0x82, 0xD5,
+            0x2D, 0xAD, 0xDE, 0x47, 0x6C, 0x5A, 0xAF, 0x86, 0x9F, 0xBA, 0x00, 0x72, 0x40, 0x93, 0x82, 0xA7,
+            0xF9, 0xBE, 0x82, 0x4E, 0x95, 0xE4, 0x2D, 0xC8, 0x0A, 0x5E, 0x2D, 0xBA, 0x4A, 0xCD, 0xAF, 0x1D,
+            0x54, 0xC7, 0x26, 0x98, 0xC1, 0x23, 0x0B, 0x50, 0xCB, 0x7D, 0x26, 0xEA, 0x81, 0xB0, 0x89, 0xF7,
+            0x93, 0x60, 0x4E, 0x94, 0x52, 0x43, 0x45, 0xC4, 0x99, 0x3E, 0x63, 0x2E, 0x18, 0x8E, 0xEA, 0xD9,
+            0xCA, 0xE7, 0x7B, 0x39, 0x98, 0xA4, 0x3E, 0xFD, 0x01, 0x9A, 0x5D, 0xD3, 0x19, 0x14, 0xB7, 0x0A,
+            0xB0, 0x4E, 0x1C, 0xED, 0x28, 0xEA, 0x22, 0x10, 0x29, 0x70, 0x7F, 0xC3, 0x30, 0x64, 0xC8, 0xC9,
+            0xE8, 0xA6, 0xC1, 0xE9, 0xC0, 0x4C, 0xE3, 0xF9, 0xE9, 0x3C, 0x9C, 0x3A, 0xD9, 0x58, 0x54, 0xF3,
+            0xB4, 0x86, 0xCC, 0xDC, 0x74, 0xCA, 0x2F, 0x25, 0x9D, 0xF6, 0xB3, 0x1F, 0x44, 0xAE, 0xE7, 0xEC])
+
+    def test_pad_block(self):
+        block = [0x21, 0xA0, 0x43, 0xFF]
+
+        self.assertEqual(pad_block(block, 'pkcs7'),
+                         block + [0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C, 0x0C])
+
+        self.assertEqual(pad_block(block, 'iso7816'),
+                         block + [0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])
+
+        self.assertEqual(pad_block(block, 'whitespace'),
+                         block + [0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20])
+
+        self.assertEqual(pad_block(block, 'zero'),
+                         block + [0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])
+
+        block = list(range(16))
+        for mode in ('pkcs7', 'iso7816', 'whitespace', 'zero'):
+            self.assertEqual(pad_block(block, mode), block, mode)
+
 
 if __name__ == '__main__':
     unittest.main()

yt_dlp/aes.py

@@ -31,6 +31,33 @@ def unpad_pkcs7(data):
 BLOCK_SIZE_BYTES = 16
 
 
+def pad_block(block, padding_mode):
+    """
+    Pad a block with the given padding mode
+    @param {int[]} block        block to pad
+    @param padding_mode         padding mode
+    """
+    padding_size = BLOCK_SIZE_BYTES - len(block)
+
+    PADDING_BYTE = {
+        'pkcs7': padding_size,
+        'iso7816': 0x0,
+        'whitespace': 0x20,
+        'zero': 0x0,
+    }
+
+    if padding_size < 0:
+        raise ValueError('Block size exceeded')
+    elif padding_mode not in PADDING_BYTE:
+        raise NotImplementedError(f'Padding mode {padding_mode} is not implemented')
+
+    if padding_mode == 'iso7816' and padding_size:
+        block = block + [0x80]  # NB: += mutates list
+        padding_size -= 1
+
+    return block + [PADDING_BYTE[padding_mode]] * padding_size
+
+
 def aes_ecb_encrypt(data, key, iv=None):
     """
     Encrypt with aes in ECB mode
@@ -137,13 +164,14 @@ def aes_cbc_decrypt(data, key, iv):
     return decrypted_data
 
 
-def aes_cbc_encrypt(data, key, iv):
+def aes_cbc_encrypt(data, key, iv, padding_mode='pkcs7'):
     """
-    Encrypt with aes in CBC mode. Using PKCS#7 padding
+    Encrypt with aes in CBC mode
 
     @param {int[]} data        cleartext
     @param {int[]} key         16/24/32-Byte cipher key
     @param {int[]} iv          16-Byte IV
+    @param padding_mode        Padding mode to use
     @returns {int[]}           encrypted data
     """
     expanded_key = key_expansion(key)
@@ -153,8 +181,8 @@ def aes_cbc_encrypt(data, key, iv):
     previous_cipher_block = iv
     for i in range(block_count):
         block = data[i * BLOCK_SIZE_BYTES: (i + 1) * BLOCK_SIZE_BYTES]
-        remaining_length = BLOCK_SIZE_BYTES - len(block)
-        block += [remaining_length] * remaining_length
+        block = pad_block(block, padding_mode)
+
         mixed_block = xor(block, previous_cipher_block)
 
         encrypted_block = aes_encrypt(mixed_block, expanded_key)
@@ -510,5 +538,6 @@ __all__ = [
     'aes_gcm_decrypt_and_verify',
     'aes_gcm_decrypt_and_verify_bytes',
     'key_expansion',
+    'pad_block',
     'unpad_pkcs7',
 ]