You can’t see me, I’m obfuscating (on Windows Phone)
Published on November 17, 2010 by Sebastian Holst
Recent communications from Microsoft have resulted in a wave of interest (to put it mildly) in obfuscation. Obfuscation is not new; nor are most of the questions, concerns, and critiques that have started flying around the WP7 dev community – but some are (because there are some unique aspects to the wp7 environment).
I have included some resources and comments here – but also, please stay tuned as PreEmptive will be pushing out a collection of resources on this subject specifically targeting Windows Phone.
Quick resources available now:
ISSA Journal: Assessing and Managing Security Risks Unique to Java and .NET (pdf). Tries to answer the questions “when and why should I worry?” and “then what can I do about it?” Specifically, this article “enumerates specific risks unique to managed code (.NET and Java), offers guidance on assessing organizational materiality of these risks, and lists broadly recognized risk mitigation technologies and practices.”
WP7 FAQ (short blog form)
Question: Why do I have to obfuscate my Windows Phone application? Has Microsoft dropped the ball?
Answer: You don’t have to – but if you want to prevent easy reverse engineering of your application, then you should. Managed code has always been easy to reverse engineer (see ISSA Article listed above), and WP7 is no better or worse. In fact, it may be helpful to compare Android’s policy and recommendations on obfuscation – see my blog here for a detailed comparison.
Question: I just obfuscated my application and it’s broken! Is this a bug? Why can’t it just work like encryption?
Answer: Obfuscation is fundamentally different than encryption in that meaning matters.
Encryption is only half of the equation – the other half is decryption . Encryption algorithms do not need to preserve the meaning of content because the content will be decrypted . Meaning is wiped out in the output (that is the intent of course) and a reconstituted at decryption time (that also means that encryption cannot be lossy).
Obfuscation is the entire equation – there is no “de-obfuscation” – in fact, that is its intent. Meaning must be preserved in the final output. When your program has tricky reflection, includes mixed-mode DLLs, incorporates 3rd party libraries, etc. – all of that must be accounted for. Some of this can be divined through static analysis – but some idioms/semantics cannot.
Question: I just want to keep Reflector from showing source code. Is that so hard?
Answer: That is actually easy. Turn-off renaming and turn-on “control flow.” The ISSA article defines these transforms, but the short answer is that renaming confuses humans and control flow confuses programs. Renaming is almost always the culprit when it comes to “breaking apps.”
Question: Where can I go to learn about the latest resources to help me obfuscate my app?
Answer: Go to www.preemptive.com/application-protection – we will update this page regularly. Also, follow us on Twitter – @PreEmptive