diff --git a/oletools/crypto.py b/oletools/crypto.py
index fc45d8d..0b32c12 100644
--- a/oletools/crypto.py
+++ b/oletools/crypto.py
@@ -88,6 +88,9 @@ import struct
 import os
 from os.path import splitext, isfile
 from tempfile import mkstemp
+from oletools.common.errors import CryptoErrorBase, WrongEncryptionPassword, \
+    UnsupportedEncryptionError, MaxCryptoNestingReached
+from olefile import OleFileIO
 
 try:
     import msoffcrypto
@@ -95,6 +98,11 @@ except ImportError:
     msoffcrypto = None
 
 
+#: if there is an encrypted file embedded in an encrypted file,
+#: how deep down do we go
+MAX_NESTING_DEPTH = 10
+
+
 def is_encrypted(olefile):
     """
     Determine whether document contains encrypted content.