How Can We Effectively Obfuscate Strings Embedded in Executable Binaries?

Obfuscating Strings in Binary Code

Problem Statement

Obfuscating strings embedded within executable binaries is valuable for protecting sensitive information like encryption keys from unauthorized access. However, straightforward methods like storing the string in a character array can easily reveal its contents during analysis.

Solution

To effectively hide strings in compiled binaries, a more sophisticated approach can be employed. Consider the following example:

#include "HideString.h"

DEFINE_HIDDEN_STRING(EncryptionKey, 0x7f, ('M')('y')(' ')('s')('t')('r')('o')('n')('g')(' ')('e')('n')('c')('r')('y')('p')('t')('i')('o')('n')(' ')('k')('e')('y'))
DEFINE_HIDDEN_STRING(EncryptionKey2, 0x27, ('T')('e')('s')('t'))

int main()
{
    std::cout << GetEncryptionKey() << std::endl;
    std::cout << GetEncryptionKey2() << std::endl;

    return 0;
}

This code incorporates a custom macro, "DEFINE_HIDDEN_STRING," to encrypt the given string. The macro encodes each character using a unique key derived from the provided seed value (e.g., "My strong encryption key" -> 0x7f). An encryption algorithm based on the seed is applied to the character sequence, making the resulting data appear random and difficult to identify in the compiled binary.

#define CRYPT_MACRO(r, d, i, elem) (elem ^ (d - i))

#define DEFINE_HIDDEN_STRING(NAME, SEED, SEQ) \
static const char* BOOST_PP_CAT(Get, NAME)() \
{ \
    static char data[] = { \
        BOOST_PP_SEQ_ENUM(BOOST_PP_SEQ_FOR_EACH_I(CRYPT_MACRO, SEED, SEQ)), \
        '' \
    }; \
    static bool isEncrypted = true; \
    if (isEncrypted) \
    { \
        for (unsigned i = 0; i < (sizeof(data) / sizeof(data[0])) - 1; ++i) \
        { \
            data[i] = CRYPT_MACRO(_, SEED, i, data[i]); \
        } \
        isEncrypted = false; \
    } \
    return data; \
}

This approach effectively obfuscates the embedded strings within the binary code, making them difficult to extract without knowledge of the encryption key and algorithm. It strikes a balance between security and ease of use, offering a convenient method to protect sensitive information.

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