Source available on GitHub

Obfuscate

Guaranteed compile-time string literal obfuscation header-only library for C++14.

Quick start guide

1. Copy obfuscate.h into your project
2. Wrap strings with AY_OBFUSCATE("My String")

Now your project will not expose those strings in plain text in the binary image.

Note that these strings will still be accessible to determined hackers. Using obfuscation to hide private passwords or any other security sensitive strings is not recommended by the author.

Whats the problem?

When plain text string literals are used in C++ programs, they will be compiled as-is into the resultant binary. This causes them to be incredibly easy to find. One can simply open up the binary file in a text editor to see all of the embedded string literals in plain view. A special utility called strings exists which can be used to search binary files for plain text strings.

What does this library do?

This header-only library seeks to make it difficult (but not impossible) for embedded string literals in binary files to be found by encrypting them with an XOR cipher at compile-time using a constant expression, forcing the compiler to work with the encrypted string instead of the plain text literal. Usage of AY_OBFUSCATE additionally removes the need for a const pointer to the string, which more often than not (for small strings) convinces the compiler to inline the encrypted string, building it up at runtime in a series of assembly operations, protecting the binary image against simple XOR decryption attacks. Encrypted strings will then be decrypted at runtime to be utilised within the program.

Technical features

• Guaranteed compile-time obfuscation - the string is compiled with a constexpr expression.
• Global lifetime (per-thread) - the obfuscated string is stored in a thread local variable in a unique lambda.
• Implicitly convertible to a char* - easy to integrate into existing codebases.
• Random 64-bit key - obfusated with a random key each time.

By simply wrapping your string literal "My String" with AY_OBFUSCATE("My String") it will be encrypted at compile time with a random 64 bit key and stored in an ay::obfuscated_data object which you can manipulate at runtime. For convenience it is also implicitly convertable to a char*.

For example, the following program will not store the string "Hello World" in plain text anywhere in the compiled executable.

#include "obfuscate.h"

int main()
{
    std::cout << AY_OBFUSCATE("Hello World") << std::endl;
    return 0;
}

Examples of usage

Because the obfuscated string that is generated by AY_OBFUSCATE has global lifetime per-thread, it is completely fine to also use it in both a local and a temporary context.

char* var = AY_OBFUSCATE("string");
const char* var = AY_OBFUSCATE("string");
static const char* var = AY_OBFUSCATE("string");
std::string var(AY_OBFUSCATE("string"));
function_that_takes_char_pointer(AY_OBFUSCATE("string"));

Thread safety

This library can be used in a multi-threaded environment only if AY_OBFUSCATE is used in a local context per thread. This is because the obfuscated string is internally stored with thread_local storage. The following usage is supported:

void fun()
{
    auto var = AY_OBFUSCATE("Thread Safe");
    var.decrypt();
    std::cout << var << std::endl;
    var.encrypt();
}

int main()
{
    std::thread thread1(fun);
    std::thread thread2(fun);

    thread1.join();
    thread2.join();
    return 0;
}

Conversely, sharing an obfuscated string returned from AY_OBFUSCATE between multiple threads is not supported. In this case you must put locks in appropriate places in your code to ensure that only one thread accesses it at a time. The following usage is not supported:

int main()
{
    for (size_t i = 0; i < 1000; i++)
    {
        auto var = AY_OBFUSCATE("NOT Thread Safe");
        var.decrypt();
        
        std::thread thread([&var]() {
            std::cout << var << std::endl;
        });
        
        // We are encrypting the string here, but outputting it in
        // another thread at the same time. This will not work.
        var.encrypt();

        thread.join();
    }
    return 0;
}

Binary file size overhead

This does come at a small cost. In a very naive login program, which obfuscates two strings (username and password) the following binary file bloat exists.

Config	Plain string literals	Obfuscated strings	Bloat
Release	18944	21504	2560 (13.5%)
Debug	95232	101888	6656 (7.0%)

This output is generated by running test_bloat.py