In software development, manual obfuscation is the deliberate act of creating obfuscated code, i.e. source or machine code that is difficult for humans to understand. Like obfuscation in natural language, it may use needlessly roundabout expressions to compose statements. Programmers may deliberately obfuscate code to conceal its purpose (security through obscurity) or its logic, in order to prevent tampering, deter reverse engineering, or as a puzzle or recreational challenge for someone reading the source code.
Contents
- Overview
- Recreational obfuscation
- Examples
- Advantages of obfuscation
- Disadvantages of obfuscation
- Obfuscating software
- Obfuscation and copyleft licenses
- References
In addition, tools known as obfuscators can provide automated obfuscation to compiled applications that make reverse engineering more difficult for people and machines but do not alter the behavior of the obfuscated application.
Overview
The architecture and characteristics of some languages may make them easier to obfuscate than others. C, C++, and the Perl programming language are some examples of languages easy to obfuscate.
Recreational obfuscation
Writing and reading obfuscated source code can be a brain teaser for programmers. A number of programming contests reward the most creatively obfuscated code: the International Obfuscated C Code Contest, Obfuscated Perl Contest, and International Obfuscated Ruby Code Contest.
Types of obfuscations include simple keyword substitution, use or non-use of whitespace to create artistic effects, and self-generating or heavily compressed programs.
Short obfuscated Perl programs may be used in signatures of Perl programmers. These are JAPHs ("Just another Perl hacker").
Examples
This is a winning entry from the International Obfuscated C Code Contest written by Ian Phillipps in 1988 and subsequently reverse engineered by Thomas Ball.
It is a C program that when compiled and run will generate the 12 verses of The 12 Days of Christmas. It contains all the strings required for the poem in an encoded form within the code.
A non-winning entry from the same year, this next example illustrates creative use of whitespace; it generates mazes of arbitrary length:
Modern C compilers don't allow constant strings to be overwritten, which can be avoided by changing "*M" to "M[3]" and omitting "M=".
The following example by Óscar Toledo Gutiérrez, Best of Show entry in the 19th IOCCC, implements an 8080 emulator complete with terminal and disk controller, capable of booting CP/M-80 and running CP/M applications:
An example of a JAPH:
This slowly displays the text "Just another Perl / Unix hacker", multiple characters at a time, with delays. An explanation can be found here.
Some Python examples can be found in the official Python programming FAQ.
Advantages of obfuscation
There are several advantages of automated code obfuscation that have made it popular and widely useful across many platforms. On some platforms (such as Java., Android, and .NET) a free tool called decompiler can easily reverse-engineer source code from an executable or library. A main advantage of automated code obfuscation is that it helps protect the trade secrets (intellectual property) contained within software by making reverse-engineering a program difficult and economically unfeasible. Other advantages might include helping to protect licensing mechanisms and unauthorized access, and shrinking the size of the executable.
Disadvantages of obfuscation
While obfuscation can make reading, writing and reverse-engineering a program difficult and time-consuming, it will not necessarily make it impossible. Some anti-virus software, such as AVG, will also alert their users when they land on a site with code that is manually obfuscated, as one of the purposes of obfuscation can be to hide malicious code. However, some developers may employ code obfuscation for the purpose of reducing file size or increasing security. The average user may not expect their antivirus software to provide alerts about an otherwise harmless piece of code, especially from trusted corporations, so such a feature may actually serve as a deterrent.
Obfuscating software
A variety of tools exist to perform or assist with code obfuscation. These include experimental research tools created by academics, hobbyist tools, commercial products written by professionals, and open-source software. There also exist deobfuscation tools that attempt to perform the reverse transformation.
Although the majority of commercial obfuscation solutions work by transforming either program source code, or platform-independent bytecode as used by Java and .NET, there are also some that work directly on compiled binaries.
Obfuscation and copyleft licenses
There has been debate on whether it is illegal to skirt copyleft software licenses by releasing source code in obfuscated form, such as in cases in which the author is less willing to make the source code available. The issue is addressed in the GNU General Public License by defining source code as the "preferred" version of the source code be made available. The GNU website states "Obfuscated 'source code' is not real source code and does not count as source code."