diff --git a/gui/Gui/Makeimage.py b/gui/Gui/Makeimage.py
index b0c30e7..e641429 100644
--- a/gui/Gui/Makeimage.py
+++ b/gui/Gui/Makeimage.py
@@ -53,7 +53,7 @@ def writeGraph(attackthread,txt,fp):
     ALL = 3
 
     def graphLine(txt):
-        fp.write("\t%s;\n" % (txt))
+        fp.write(("\t%s;\n" % (txt)).encode('utf-8'))
 
     def setAttr(atxt,EdgeNodeDefAll=ALL):
         if EdgeNodeDefAll == ALL:
@@ -81,7 +81,7 @@ def writeGraph(attackthread,txt,fp):
 
     # write all graph lines but add layout modifiers
     for l in txt.splitlines():
-        fp.write(l)
+        fp.write(l.encode('utf-8'))
         if l.startswith("digraph"):
             # Write additional stuff for this graph
             #
@@ -147,7 +147,7 @@ def makeImageDot(dotdata,attackthread=None):
     p.stdin.close()
 
     for l in p.stdout.read():
-        f.write(l)
+        f.write(str(l))
 
     p.stdout.close()
     f.flush()
diff --git a/gui/Scyther/FindDot.py b/gui/Scyther/FindDot.py
index 116f8dd..077326c 100644
--- a/gui/Scyther/FindDot.py
+++ b/gui/Scyther/FindDot.py
@@ -41,8 +41,9 @@ def testDot(fpath):
     try:
         cmd = "%s -V" % (fpath)
         (sts,sout,serr) = Misc.safeCommandOutput(cmd)
+
         if sts != -1:
-            if "version" in sout + serr:
+            if "version" in str(sout) + str(serr):
                 return True
     except:
         pass
diff --git a/gui/Scyther/Scyther.py b/gui/Scyther/Scyther.py
index ad173ae..ba88f74 100755
--- a/gui/Scyther/Scyther.py
+++ b/gui/Scyther/Scyther.py
@@ -294,14 +294,18 @@ class Scyther(object):
 
         # Apparently we are supporsed to be able to use the cache
         m = hashlib.sha256()
+        
+        def muppet(m, s):
+            m.update(s.encode('utf-8'))
+
         if spdl == None:
-            m.update("[spdl:None]")
+            muppet(m, "[spdl:None]")
         else:
-            m.update(spdl)
+            muppet(m, spdl)
         if args == None:
-            m.update("[args:None]")
+            muppet(m, "[args:None]")
         else:
-            m.update(args)
+            muppet(m, args)
 
         uid = m.hexdigest()
 
@@ -399,7 +403,7 @@ class Scyther(object):
             (fdi,fni) = tempfile.mkstemp()  # input
 
             # Write (input) file
-            fhi = os.fdopen(fdi,'w+b')
+            fhi = os.fdopen(fdi,'w+')
             fhi.write(spdl)
             fhi.close()
 
@@ -495,7 +499,7 @@ class Scyther(object):
                     # whoohee, xml
                     self.validxml = True
 
-                    xmlfile = StringIO.StringIO(output)
+                    xmlfile = io.StringIO(output)
                     reader = XMLReader.XMLReader()
                     self.claims = reader.readXML(xmlfile)
 
@@ -595,10 +599,10 @@ def FindProtocols(path="",filterProtocol=None):
     Note: Unix only! Will not work under windows.
     """
 
-    import commands
+    import subprocess
 
     cmd = "find %s -iname '*.spdl'" % (path)
-    plist = commands.getoutput(cmd).splitlines()
+    plist = subprocess.getoutput(cmd).splitlines()
     nlist = []
     for prot in plist:
         if filterProtocol != None:
diff --git a/gui/scyther-gui.py b/gui/scyther-gui.py
index e558bf3..863f35b 100755
--- a/gui/scyther-gui.py
+++ b/gui/scyther-gui.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 """
 	Scyther : An automatic verifier for security protocols.
 	Copyright (C) 2007-2013 Cas Cremers
@@ -193,7 +193,7 @@ class ScytherApp(wx.App):
 
         # License option may abort here
         if opts.license:
-            print Scyther.GetLicense()
+            print(Scyther.GetLicense())
             sys.exit(0)
 
         # Load preferences file
diff --git a/gui/scyther.py b/gui/scyther.py
index 4b39568..41b39f9 100755
--- a/gui/scyther.py
+++ b/gui/scyther.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """
 	Scyther : An automatic verifier for security protocols.
 	Copyright (C) 2007-2013 Cas Cremers