Swift compiler as a library: obfuscator case

Presented during Mobile Warsaw meetup on 22nd of May 2018

Transcript

1. Swift compiler as a
   library: 

   obfuscator case
   Krzysztof Siejkowski
   

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2. 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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3. App Store
   YourApp binary file
   Your source code
   

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

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5. 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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6. 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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7. 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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12. class MyViewController: UIViewController {}
    class MyView: UIView {}
    class MyModel: NSManagedObject {}
    class MyRuntimeUsingObject: NSObject {}
    class SomeClass {
    @objc func someFunc() {}
    }
    

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13. Obfuscation is more
    than symbol renaming
    

    Code Obfuscation Techniques for Software Protection

    —PhD thesis by Jan Cappaert

    

    

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

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

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

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17. Before compilation:
    source to source
    WE!!!
    

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18. Goal: obfuscate Swift
    code 

    by renaming
    

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21. Does it work?
    

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22. Does it work?
    YES
    

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

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

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

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26. 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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27. 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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28. Original Xcode project
    Xcode project parsing
    

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29. Original Xcode project
    Xcode project parsing
    Symbols identification
    

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

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

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32. 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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33. 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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42. 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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50. 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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56. 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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59. 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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61. Abstract 

    Syntax 

    Tree
    

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62. 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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63. 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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64. ParamDecl *Parameter = //given from SourceEntityWalker
    auto Name = Parameter ->getName().str().str();
    CharSourceRange Range(Parameter ->getNameLoc(),
    Name.length());
    

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65. 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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67. 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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68. void MappingTraits ::
    mapping(IO &Io, SymbolsJson &Object) {
    Io.mapRequired("symbols", Object.Symbols);
    }
    Input Input(JsonString);
    SymbolsJson Symbols;
    Input >> Symbols;
    

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69. • 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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70. 1. Get familiar with C++11
    Few last practical tips
    

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71. 1. Get familiar with C++11

    2. Use Xcode as IDE (works really well!)
    Few last practical tips
    

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72. 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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73. 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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75. Pros Cons
    Anything compiler can do,
    you can do too!
    

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

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77. 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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78. 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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79. 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
    

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80. 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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81. 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
    Support for both 

    Swift and Objective-C
    

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82. 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
    Support for both 

    Swift and Objective-C
    There might be
    better alternatives
    

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83. Alternatives
    • libSyntax
    • SourceKit
    • existing swift tools
    

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85. • https://github.com/PolideaPlayground/
    SiriusObfuscator-SymbolExtractorAndRenamer 

    • Documentation folder has a lot of notes 

    on various implementation decisions, 

    with details and motivation
    

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87. 
    @KacperHarasim
    

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88. Questions?
    @_siejkowski
    

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89. Thank you!
    

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