CODEWITHSUNDEEP
c++stringmacros
noober
noober

Reputation: 4938

String modification in C++ macro

Is there a way to modify a string literal in C++ from macro?

The reason for that is obfuscating code, particularly, 2 mutex wishes:

  1. I want to see literals as is in my source code, say, "password123".
  2. I want them to be mangled somehow before compilation to avoid including them in binaries.

I know that primitive modifications like XOR or shifting cannot be enough for professional analysis, but they are good enough for me.

Upvotes: 0

Views: 279

Answers (2)

Potatoswatter
Potatoswatter

Reputation: 137770

You can use the macro to pass the string to a constexpr function which does the "encryption." Since C++14, constexpr is much easier to use.

// Similar to std::array, but with a member pointer as an accessor.
// It's complicated.
template< std::size_t length >
struct string_holder {
    char str[ length ];
    char const * ptr = str;
};

template< std::size_t length >
constexpr string_holder< length > encrypt( char const (& in)[ length ] ) {
    string_holder< length > result = {};
    for ( std::size_t i = 0; i != length - 1; ++ i ) {
        result.str[ i ] = in[ i ] ^ 1; // Do encryption here.
    }
    return result;
}

#define ENCRYPT( STR ) ( encrypt( STR ).ptr )

char const * const & s = ENCRYPT( "password123" );

http://coliru.stacked-crooked.com/a/3b6f6753d9f722cb

Note, s needs to be declared as a const& reference to take advantage of lifetime extension. You could also write auto const& s or auto &&s; it would be the same. The current version of Clang does not allow s to be declared constexpr, but I believe this to be a bug.

Ideally, you could just write a user-defined literal like "password123"_encrypted. Unfortunately, progress on implementing the underlying language features for that is slow.

Upvotes: 3

mark
mark

Reputation: 5459

You could create a macro that doesn't really do anything, but use the macro as a "marker" for a custom build step (simple script might do it) to obfuscate the strings prior to the preprocessor getting the source code.

Upvotes: 3

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