diff --git a/pyrad/packet.py b/pyrad/packet.py
index ecaa5a2..82902af 100644
--- a/pyrad/packet.py
+++ b/pyrad/packet.py
@@ -740,7 +740,7 @@ def VerifyChapPasswd(self, userpwd):
         challenge = self.authenticator
         if 'CHAP-Challenge' in self:
             challenge = self['CHAP-Challenge'][0]
-        return password == md5_constructor(b'%s%s%s' % (chapid, userpwd, challenge)).digest()
+        return password == md5_constructor(chapid + userpwd + challenge).digest()
 
     def VerifyAuthRequest(self):
         """Verify request authenticator.
diff --git a/pyrad/tools.py b/pyrad/tools.py
index 8d2b37f..3ddb33e 100644
--- a/pyrad/tools.py
+++ b/pyrad/tools.py
@@ -110,10 +110,10 @@ def EncodeAscendBinary(str):
             terms[key] = struct.pack('B', int(value))
 
     trailer = 8 * b'\x00'
-    result = b'%s%s%s\x00%s%s%s%s%s\x00%s%s%s%s\x00\x00' % (
-        terms['family'], terms['action'], terms['direction'], terms['src'],
-        terms['dst'], terms['srcl'], terms['dstl'], terms['proto'],
-        terms['sport'], terms['dport'], terms['sportq'], terms['dportq']) + trailer
+
+    result = b''.join((terms['family'], terms['action'], terms['direction'], b'\x00', 
+        terms['src'], terms['dst'], terms['srcl'], terms['dstl'], terms['proto'], b'\x00',
+        terms['sport'], terms['dport'], terms['sportq'], terms['dportq'], b'\x00\x00', trailer))
     return result