diff --git a/src/saml2/sigver.py b/src/saml2/sigver.py
index fa5fc8d..8e24a76 100644
--- a/src/saml2/sigver.py
+++ b/src/saml2/sigver.py
@@ -828,7 +828,7 @@ class CryptoBackendXmlSec1(CryptoBackend):
         (_stdout, _stderr, output) = self._run_xmlsec(com_list, [fil],
                                                       exception=DecryptError,
                                                       validate_output=False)
-        return output
+        return output.decode('utf-8')
 
     def sign_statement(self, statement, node_name, key_file, node_id,
                        id_attr):
diff --git a/tests/test_50_server.py b/tests/test_50_server.py
index 61f7ad3..1c3a081 100644
--- a/tests/test_50_server.py
+++ b/tests/test_50_server.py
@@ -706,7 +706,7 @@ class TestServer1():
 
         assert valid
 
-        _, key_file = make_temp("%s" % cert_key_str, decode=False)
+        _, key_file = make_temp(cert_key_str, decode=False)
 
         decr_text = self.server.sec.decrypt(decr_text, key_file)
 
@@ -749,7 +749,7 @@ class TestServer1():
 
         assert sresponse.signature is None
 
-        _, key_file = make_temp("%s" % cert_key_str_advice, decode=False)
+        _, key_file = make_temp(cert_key_str_advice, decode=False)
 
         decr_text = self.server.sec.decrypt(_resp, key_file)
 
@@ -781,7 +781,7 @@ class TestServer1():
 
         decr_text_1 = self.server.sec.decrypt(_resp, self.client.config.key_file)
 
-        _, key_file = make_temp("%s" % cert_key_str_advice, decode=False)
+        _, key_file = make_temp(cert_key_str_advice, decode=False)
 
         decr_text_2 = self.server.sec.decrypt(decr_text_1, key_file)
 
@@ -812,7 +812,7 @@ class TestServer1():
 
         assert sresponse.signature is None
 
-        _, key_file = make_temp("%s" % cert_key_str_assertion, decode=False)
+        _, key_file = make_temp(cert_key_str_assertion, decode=False)
 
         decr_text = self.server.sec.decrypt(_resp, key_file)
 
@@ -904,11 +904,11 @@ class TestServer1():
 
         assert sresponse.signature is None
 
-        _, key_file = make_temp("%s" % cert_key_str_assertion, decode=False)
+        _, key_file = make_temp(cert_key_str_assertion, decode=False)
 
         decr_text_1 = _server.sec.decrypt(_resp, key_file)
 
-        _, key_file = make_temp("%s" % cert_key_str_advice, decode=False)
+        _, key_file = make_temp(cert_key_str_advice, decode=False)
 
         decr_text_2 = _server.sec.decrypt(decr_text_1, key_file)
 
diff --git a/tests/test_60_sp.py b/tests/test_60_sp.py
index 36d2723..6448d6d 100644
--- a/tests/test_60_sp.py
+++ b/tests/test_60_sp.py
@@ -64,7 +64,7 @@ class TestSP():
             "urn:mace:example.com:saml:roland:sp", trans_name_policy,
             "foba0001@example.com", authn=AUTHN)
 
-        resp_str = base64.encodestring(resp_str)
+        resp_str = base64.encodestring(resp_str.encode('utf-8'))
         self.sp.outstanding_queries = {"id1": "http://www.example.com/service"}
         session_info = self.sp._eval_authn_response(
             {}, {"SAMLResponse": [resp_str]})