diff --git a/auth/lib.py b/auth/lib.py
index 8592cad86..160cd67e7 100644
--- a/auth/lib.py
+++ b/auth/lib.py
@@ -8,10 +8,11 @@ import base64
 from modoboa.lib import parameters
 
 def encrypt(clear):
-    obj = AES.new(parameters.get_admin("SECRET_KEY"),
-                  AES.MODE_ECB)
+    key = parameters.get_admin("SECRET_KEY")
+    obj = AES.new(key, AES.MODE_ECB)
+    clear = str(clear)
     if len(clear) % AES.block_size:
-        clear += "\0" * (AES.block_size - len(clear) % AES.block_size)
+        clear += " " * (AES.block_size - len(clear) % AES.block_size)
     ciph = obj.encrypt(clear)
     ciph = base64.b64encode(ciph)
     return ciph
@@ -20,7 +21,7 @@ def decrypt(ciph):
     obj = AES.new(parameters.get_admin("SECRET_KEY"), AES.MODE_ECB)
     ciph = base64.b64decode(ciph)
     clear = obj.decrypt(ciph)
-    return clear.rstrip('\0')
+    return clear.rstrip(' ')
 
 def get_password(request):
     return decrypt(request.session["password"])