Swift compiler as a library: obfuscator case

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Swift compiler as a library:   obfuscator case Krzysztof Siejkowski

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In software development, obfuscation is the deliberate act of creating source or machine code that is difficult for humans to understand — Wikipedia

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App Store YourApp binary ﬁle Your source code

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App Store YourApp binary ﬁle YourApp encrypted (FairPlay) Jailbroken device YourApp binary ﬁle Your source code

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App Store YourApp binary file YourApp encrypted (FairPlay) YourApp decrypted (in memory) Memory dump tool YourApp binary file Jailbroken device YourApp binary file Your source code

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App Store YourApp binary ﬁle YourApp encrypted (FairPlay) YourApp decrypted (in memory) Memory dump tool YourApp binary ﬁle Your source code Disassembler (Hopper) Assembly/pseudo-code Jailbroken device

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class MyViewController: UIViewController {} class MyView: UIView {} class MyModel: NSManagedObject {} class MyRuntimeUsingObject: NSObject {} class SomeClass { @objc func someFunc() {} }

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Obfuscation is more than symbol renaming   Code Obfuscation Techniques for Software Protection  —PhD thesis by Jan Cappaert   

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How to obfuscate? • after compilation • during compilation • before compilation

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After compilation: binary to binary iXGuard (https://www.guardsquare.com/en/ixguard)

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During compilation: source to binary Obfuscator-LLVM (https://github.com/obfuscator-llvm/obfuscator)

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Before compilation: source to source WE!!!

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Goal: obfuscate Swift code   by renaming

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Does it work?

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Does it work? YES

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Not universal tool… • no DSYM support • no multiple targets • no mixed Swift/Obj-C • not all Swift constructs supported

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…but still powerful • Storyboards/XIBs renaming • various Swift expressions supported • excluding conﬁguration • very easy to integrate

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$ bin/sirius -help USAGE: sirius -projectrootpath [PROJECTROOTPATH] -obfuscatedproject [OBFUSCATEDPROJECTPATH]

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Xcode project Zobfuskowany Xcode project Command line interface (standalone or as Xcode build step) Original Xcode project Obfuscated Xcode project (copy or inplace)

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Original Xcode project Xcode project parsing Symbols identiﬁcation Generation of new names Obfuscated Xcode project (copy or inplace) Renaming in the source ﬁles

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Original Xcode project Xcode project parsing

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Original Xcode project Xcode project parsing Symbols identiﬁcation

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Original Xcode project Xcode project parsing Symbols identiﬁcation Generation of new names

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Original Xcode project Xcode project parsing Symbols identiﬁcation Generation of new names Obfuscated Xcode project Renaming in the source ﬁles

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Obfuscation verification Original Xcode project Xcode project parsing Symbols identification Generation of new names Obfuscated Xcode project Renaming in the source files Main command line interface

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Obfuscation verification Original Xcode project Xcode project parsing Obfuscated Xcode project Main command line interface Swift compiler Symbols identification Generation of new names Renaming in the source files

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1. create new folder in swift/tools  2. add add_swift_tool_subdirectory function   to swift/tools/CMakeLists.txt  3. create new .cpp file with main function   4. create new CMakeLists.txt for your tool  5. add add_swift_host_tool function   to swift/tools//CMakeLists.txt   and define the source files, executable name and dependencies How to add new command line tool?

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1. create new folders in swift/include/swift and swift/lib  2. add your .h interfaces   to swift/include/swift/  3. add your .cpp implementations to swift/lib/  4. create CMakeLists.txt for your library   at swift/lib//CMakeLists.txt   with add_swift_library function   that deﬁnes the source ﬁles, library name and dependencies  5. add add_subdirectory function to swift/lib/CMakeLists.txt   How to add new library?

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1. create new folder in swift/unittests  2. add your .cpp test source code   to swift/unittests/  3. create CMakeLists.txt for your unit tests  at swift/unittests//CMakeLists.txt   with add_swift_unittest function that   deﬁnes the source ﬁles, executable name and dependencies  4. add add_subdirectory call to swift/unittests/CMakeLists.txt   How to add unit tests?

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1. create tool in swift/tools/  2. (not required, but a good idea) create library   for the underlying logic   in swift/include/swift/   and swift/lib/  3. add unit tests to swift/unittests/  4. add integration tests to swift/tests/  How to create new compiler-based tool?

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Abstract   Syntax   Tree

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CompilerInstance Compiler; CompilerInvocation Invocation; Invocation.setModuleName(ModuleName); Invocation.setMainExecutablePath(MainExecutablePath); for (const auto &InputFilename : InputFilenames) { Invocation.addInputFilename(InputFilename); } Invocation.setFrameworkSearchPaths(FrameworkPaths); Invocation.setSDKPath(SdkPath); Invocation.setTargetTriple(Triple); if (Compiler.setup(Invocation)) { return stringError("Error during compiler setup"); } Compiler.performSema();

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class SymbolsWalker : public SourceEntityWalker { bool visitDeclReference(ValueDecl *, CharSourceRange, TypeDecl *, ExtensionDecl *, Type, ReferenceMetaData) override; } for (auto* Unit : Compiler.getMainModule() ->getFiles()) { if (auto* Current = dyn_cast(Unit)) { SymbolsWalker Walker; Walker.walk(&Current); } }

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ParamDecl *Parameter = //given from SourceEntityWalker auto Name = Parameter ->getName().str().str(); CharSourceRange Range(Parameter ->getNameLoc(), Name.length());

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auto &SourceManager = Current ->getASTContext().SourceMgr; auto BufferId = Current ->getBufferID().getValue();  std ::error_code Error; llvm ::raw_fd_ostream DescriptorStream(Path, Error, F_None); SourceEditOutputConsumer Editor(SourceManager,   BufferId, DescriptorStream);    CharSourceRange Range = // computed slide ago auto ReplacingString = // replacement for range in code Editor ->ide ::SourceEditConsumer ::accept(SourceManager, Range, ReplacingString);

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static llvm ::cl ::opt SymbolsJsonPath("symbolsjson", llvm ::cl ::desc("Name of the file containing extracted symbols"), llvm ::cl ::cat(ObfuscatorNameMapper)); int main(int argc, char *argv[]) { INITIALIZE_LLVM(argc, argv); llvm ::cl ::ParseCommandLineOptions(argc, argv, “obfuscator-name-mapper");

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void MappingTraits :: mapping(IO &Io, SymbolsJson &Object) { Io.mapRequired("symbols", Object.Symbols); } Input Input(JsonString); SymbolsJson Symbols; Input >> Symbols;

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• LLVM Programmer’s Manual   (http://llvm.org/docs/ProgrammersManual.html)   • LLVM Coding Standards   (http://llvm.org/docs/CodingStandards.html) • many more!

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1. Get familiar with C++11 Few last practical tips

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1. Get familiar with C++11  2. Use Xcode as IDE (works really well!) Few last practical tips

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1. Get familiar with C++11  2. Use Xcode as IDE (works really well!)  3. Keep Swift compiler in sync   with Xcode version Few last practical tips

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1. Get familiar with C++11  2. Use Xcode as IDE (works really well!)  3. Keep Swift compiler in sync   with Xcode version  4. Don’t let the lack of compiler knowledge   scare you away! Few last practical tips

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Pros Cons Anything compiler can do, you can do too!

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Pros Cons Anything compiler can do, you can do too! Compiler libs are designed for compilation, not for your tool

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Pros Cons Anything compiler can do, you can do too! Compiler libs are designed for compilation, not for your tool So many tools are available!

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Pros Cons Anything compiler can do, you can do too! Compiler libs are designed for compilation, not for your tool So many tools are available! No stable API, breaking changes all the time

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Pros Cons Anything compiler can do, you can do too! Compiler libs are designed for compilation, not for your tool So many tools are available! No stable API, breaking changes all the time You can leverage   the existing infrastructure You must ﬁt into   the existing infrastructure

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Alternatives • libSyntax • SourceKit • existing swift tools

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• https://github.com/PolideaPlayground/ SiriusObfuscator-SymbolExtractorAndRenamer   • Documentation folder has a lot of notes   on various implementation decisions,   with details and motivation