Reducing the Size of .NET Applications

Executable files for the .NET Framework currently cannot be packed by binary file compressors such as UPX (http://upx.sourceforge.net/) because .NET uses customized sections in the Portable Executable (PE) file (which is used by all Windows executable files). The .NET Execution Engine expects Common Language Infrastructure (CLI) data to be in the proper sections of the PE file. However, CLI data is placed in the PE sections uncompressed by default.

This article presents a technique for reducing the size of .NET executables without using native code or otherwise modifying the PE format. Instead uses reflection, which is supported by the .NET Framework, and pack the applications at a higher level.

Reducing the size of applications has several benefits:

• The disk space required is smaller. While disk space is usually not a problem in desktop computers, it can be in portable devices that run .NET Framework.
• Smaller executables load faster because of fewer disk accesses. Even if you uncompress the data in memory, RAM access is very fast and compressed executables still load faster than the original uncompressed ones.
• Using compression combined with, say, in-memory encryption/decryption makes it harder to disassemble .NET applications. This helps protect intellectual property.

The technique does not affect the usual development of .NET applications. The application EXE file and DLL files are built and compiled as usual. The technique can be applied as an additional step after you build the release version. Because of the generality of the solution, it is possible to generalize the technique to work with generic EXE and DLL files written in any .NET front-end language. I have created a tool called .NETZ, which is based on this technique (source code and binaries are available at http://www.st.informatik .tu-darmstadt.de/static/staff/Cepa/tools/netz/index.html and from DDJ; see "Resource Center," page 5).

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Tags: executable files, .NET, file compressors, PE file, CLI, .NET framework