Hello list, This might be of some interest to someone who wants to make the reverse engineering of his software much harder. I have added scrambling for both generated code and data in TCC for i386.
You can obfuscate all calls and long jumps, the parameters passed to external functions, parameters passed to local functions, the stack, the functions prolog and epilog. You can also encrypt your code data section by XORing it with a LFSR. http://nic.ath.cx/~emil/download.html http://uglyduck.ath.cx/~emil/download.html With the 'x' switch the compiler heavily pollutes the generated code making it larger and slower. The purpose of this operation is to obfuscate the generated code and make reverse engineering harder. The 'x' switch by itself will enable all the scramble options. You may select individual scrambling features by listing them after the '-x': - 'c' obfuscate all calls - 'j' obfuscate all long jumps - 'f' obfuscate parameters passed to external (library) functions - 'p' obfuscate parameters passed to local functions - 's' obfuscate the stack (size of local variables and their references) - 'b' obfuscate functions prolog - 'e' obfuscate functions epilog (returns are replaced with jumps) - 'd' encrypt data segment with a LFSR The LFSR initial value as well as the unscrambling code is different with every compile. TCC generates read only objects in the data section (rather than rodata) so all your strings will be encrypted. Code obfuscation is mainly achieved by inserting random data between genuine operations. This tricks disassemblers because they will try to disassemble the random data. They will miss real opcodes due to variable size garbage instructions engulfing the former ones. All addressing is changed to offset addressing using a variable base (usually in ebx). This prevents disassemblers to generate any cross-references for both functions and data. The scrambling functionality is a patch against a stripped down version of tcc 0.9.25 which handles exclusively only i386 code. Both the Linux version and the cross-compiled version which generates Windows code work. The current release passes tcctest with all scrambling switches enabled. If you want to compile this compiler for a Windows platform you will probably fail (mainly because I'm using /dev/urandom). I have no plans to make it work for Windows because I'm not interested in that platform. You can generate Windows code from Linux with the cross-compiler. Generating static executables was broken on my Debian system (with stock tcc 0.9.25) so I've patched this version to use dietlibc. This has the advantage of making small executables which run on any kernel version (the bloated libc checks kernel versions and refuses to run even if you don't need any of the 2.6 functionality). The -run switch (used for C scripting) now creates (in memory) static versions of your C. This is faster and the program occupies less space. You you don't want statically linked scripts you'll have to use -rdynamic with the -run switch. -- Regards, Emil -- All my encrypted documents are safe because I use a super long passphrase. It's supercalifragilisticexpialidocious or something like that. _______________________________________________ Tinycc-devel mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/tinycc-devel
