Obfuscating Silverlight (for free)

You might be aware that when you publish a Silverlight XAP on the web, your source code is very vulnerable to prying eyes. A XAP file is in a ZIP compressed format, and the contents are .NET Assemblies and resources which can be disassembled easily using a tool like .NET Reflector . Although there is no sure-fire way to stop someone from copying your Silverlight application logic, obfuscation can at least make it a bit more difficult to hack through.
Babel Obfuscator for .NET

There are a few obfuscators out there that support Silverlight, but they can be pricey. However, Babel Obfuscator started out as a community project and still maintains a freeware edition. Additionally, it appears that the new version of Babel has corrected some issues with obfuscating Silverlight assemblies.

Here is how you can use the free edition of Babel Obfuscator to encrypt your Silverlight assemblies: (I should mention, if you do have $149 laying about, I recommend buying the Pro version of Babel which has XAP support)

1.       Download the Free edition of Babel Obfuscator.

2.       Download the Free 7-zip compression utility. We’ll need this to update the obfuscated assemblies in our Silverlight XAP file. If you are happier with a different ZIP utility, go ahead and use it instead.

3.       Inside your Silverlight solution, right-click the Silverlight project and select Properties.

4.       Go to the “Build Events” tab and add the following inside the Post-build event command line:

"C:\Program Files\Babel\babel.exe" $(TargetPath) --noildasm --nomsil --noinvalidopcodes

"C:\Program Files\7-Zip\7z.exe" a $(TargetDir)$(ProjectName).xap $(TargetDir)BabelOut\$(TargetFileName) -y -tZIP

This post-build event will run the Babel Obfuscator against your assembly, which places it into a “BabelOut” subdirectory. Then we use 7-zip to bring that updated, obfuscated assembly back into our XAP file.

Read more: andybeaulieu.com

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