diff --git i/pysimplesoap/c14n.py w/pysimplesoap/c14n.py
index 5749e49..297592e 100644
--- i/pysimplesoap/c14n.py
+++ w/pysimplesoap/c14n.py
@@ -55,11 +55,8 @@ except:
     class XMLNS:
         BASE = "http://www.w3.org/2000/xmlns/"
         XML = "http://www.w3.org/XML/1998/namespace"
-try:
-    import cStringIO
-    StringIO = cStringIO
-except ImportError:
-    import StringIO
+
+from io import StringIO
 
 _attrs = lambda E: (E.attributes and E.attributes.values()) or []
 _children = lambda E: E.childNodes or []
diff --git i/pysimplesoap/xmlsec.py w/pysimplesoap/xmlsec.py
index 2f96df7..053149f 100644
--- i/pysimplesoap/xmlsec.py
+++ w/pysimplesoap/xmlsec.py
@@ -15,7 +15,7 @@ from __future__ import print_function
 import base64
 import hashlib
 import os
-from cStringIO import StringIO
+from io import StringIO
 from M2Crypto import BIO, EVP, RSA, X509, m2
 
 # if lxml is not installed, use c14n.py native implementation